US3873784A

Acoustic transducer

Abstract

An acoustic transducer of planar shape. An electric conductor means of a coil, preferably flat spiral or flat helical configuration is operably attached to a diaphragm and positioned in the magnetic field of at least one magnetized member adjacent one of its pole faces. Magnetically conductive pole pieces preferably are positioned adjacent the magnetized member to form a dense elongated region of preferably substantially uniform magnetic flux density in said magnetic field where the electric conductor means is preferably located. Preferably said region in said magnetic field is contained in pairs of spaced apart elongated gaps formed by said pole pieces and one said magnetized member. A second diaphragm is preferably positioned adjacent the opposite pole face of one said magnetized member and preferably driven by a separate electric conductor means and the volume contained between said diaphragms is enclosed.

US3873784A, drawing sheet 1 — Sheet 1 of 47

Term

Term ended

Expired 25 March 1992, 34.5 years ago.

58 claims: 28 independent, 30 dependent

1
What is claimed is:1. A planar acoustic transducer comprising: at least one magnetized member for creating at least one magnetic field, each magnetized member having at least one substantially planar pole face;at least one electric conductor means of substantially coil shape positioned in at least one said magnetic field of at least one magnetized member and positioned substantially parallel to and spaced from at least one said planar pole face;magnetically conductive material being interlaid with and insulated from said electric conductor means to increase magnetic flux lines of said magnetic fields traversing said electric conductor means;at least one diaphragm operably attached to each said electric conductor means and positioned substantially parallel to and spaced from at least one said planar pole face;and means for supporting each said magnetized member, each said diaphragm and each said electric conductor means.
2
A planar acoustic transducer comprising:at least one magnetized member for creating at least one magnetic field, each magnetized member having at least one planar pole face;at least one pole
3
3,873,784 piece of magnetically conductive material positioned adjacent at least one said magnetized member for forming elongated regions of relatively high flux density in at least one said magnetic field; at least one electric conductor means of substantially coil shape positioned in at least one said magnetic field and forming a planar shape substantially parallel to and spaced from at least one said planar pole face; magnetically conductive material being interlaid with and insulated from said electric conductor means to increase magnetic flux lines of said magnetic fields traversing said electric conductor means; at least one planar diaphragm operably attached to at least one said electric conductor means and substantially parallel to and spaced from at least one said planar pole face, and capable of radiating reproduced sound into an ambience in a direction away from said magnetized member and said pole pieces; and means for supporting each said magnetized member, each said diaphragm and each said electric conductor means. 3. A planar acoustic transducer comprising:at least one magnetized member for creating at least one magnetic field, each magnetized member having at least one planar pole face;at least one pole piece of magnetically conductive material substantially U-shaped for forming elongated regions of relatively high flux density in at least one said magnetic field, said pole piece adjoining at least one pole face of said magnetized member conjugate to said planar pole face and extending beyond the conductor means at periphery portions thereof;at least one electric conductor means of substantially coil shape positioned in at least one said magnetic field and forming a planar shape substantially parallel to and spaced from at least one said planar pole face;at least one planar diaphragm operably attached to at least one said electric conductor means and substantially parallel to and spaced from at least one said planar pole face, and capable of radiating reproduced sound into an ambience in a direction away from said magnetized member and said pole pieces;and means for supporting each said magnetized member, each said diaphragm and each said electric conductor means.
4
A planar acoustic transducer comprising:a magnetized member for creating a magnetic field and having at least one substantially planar pole face;pole pieces of magnetically conductive material positioned adjacent the periphery of said magnetized member for forming elongated regions of relatively high flux density in said magnetic field;at least one electric conductor means of substantially coil shape concentrated in said regions of said magnetic field and spaced from each said planar pole face, said electric conductor means being substantially flat and positioned substantially parallel to magnetic flux lines of said magnetic field transversing said electric conductor means;at least one diaphragm operably attached to each said electric conductor means and positioned substantially parallel to and spaced from at least one said planar pole face, and capable of radiating reproduced sound into an ambience in a direction away from said magnetized member and said pole pieces;and means for supporting said magnetized member, said diaphragm and said electric conductor means.
5
A planar acoustic transducer comprising:a magnetized member for creating a magnetic field and having at least one substantially planar pole face;pole pieces of magnetically conductive material positioned adjacent the periphery of said magnetized member for forming elongated regions of relatively high flux density in said magnetic field;at least one electric conductor means of substantially coil shape concentrated in said regions of said magnetic field and spaced from each said planar pole face, said electric conductor means being formed of conductive pathway patterns;magnetically conductive material is interlaid with and insulated from said electric conductor means to be traversed with magnetic flux lines of said magnetic fields traversing said electric conductor means;at least one diaphragm operably attached to each said electric conductor means and positioned substantially parallel to and spaced from at least one said planar pole face, and capable of radiating reproduced sound into an ambience in a direction away from said magnetized member and said pole pieces;and means for supporting said magnetized member, said diaphragm and said electric conductor means.
6
A planar acoustic transducer comprising:at least one magnetized member for creating at least one magnetic field, each magnetized member having two substantially planar pole faces substantially parallel and conjugate to each other;at least one electric conductor means of substantially coil shape positioned substantially parallel to and spaced from each said planar pole face;at least one diaphragm operably attached to each said electric conductor means and positioned substantially parallel to and spaced from each said planar pole face;and means for supporting each said magnetized member, each said diaphragm and each said electric conductor means.
12
A planar acoustic transducer as claimed in claim 6 wherein:each said conductor means is made of conductive pathway patterns.
13
A planar acoustic transducer as claimed in claim 6 wherein:magnetically conductive material being in3,873,784 terlaid with and insulated from said electric conductor means to increase magnetic flux lines of said magnetic fields traversing through said electric conductor means.
14
A planar acoustic transducer comprising:a magnetized member for creating a magnetic field;a first pole piece of magnetically conductive material adjoining a pole face of said magnetized member;a second pole piece of substantially U-shape adjoining the conjugate pole face of said magnetized member and forming pairs of spaced apart elongated gaps with said first pole piece, said gaps containing regions of relatively high flux density in said magnetic field;electric conductor means of substantially coil shape positioned at least partially in said gaps and substantially parallel to magnetic flux lines of said magnetic fields in said gaps;a planar diaphragm operably attached to said electric conductor means;and means for supporting said magnetized member, said pole pieces, said diaphragm and said electric conductor means.
16
A planar acoustic transducer comprising:a magnetized member for creating a magnetic field;pole pieces positioned adjacent the periphery of the magnetized member to form pairs of spaced apart elongated gaps with said magnetized member, said gaps containing regions of relatively high flux density of said magnetic field;at least one electric conductor means of substantially coil shape positioned at least partially in said gaps, each said conductor means being made of conductive pathway patterns;a planar diaphragm operably attached to each said electric conductor means;and means for supporting said magnetized member, each said diaphragm and each said electric conductor means.
18
A planar acoustic transducer comprising:a magnetized member for creating a magnetic field and having a periphery;pole pieces positioned adjacent the periphery of the magnetized member to form pairs of spaced apart elongated gaps with said magnetized member, said gaps containing regions of relatively high flux density of said magnetic field;at least one electric conductor means of substantially coil shape positioned at least partially in said gaps, and substantially parallel to magnetic flux lines of said magnetic field in said gaps;at least two planar diaphragms substantially parallel to each other and operably attached to said electric conductor means;and means for supporting said magnetized member, each said diaphragm and each said electric conductor means.
19
A planar acoustic transducer comprising:a magnetized member for creating a magnetic field and having a periphery;pole pieces of magnetically conductive material adjoining opposed pole faces of said magnetized member;pole pieces positioned adjacent the periphery of the magnetized member to form at least two pairs of spaced apart elongated gaps with said first mentioned pole pieces, said gaps containing regions of relatively high flux density in said magnetic field at least;at least two electric conductor means of substantially coil shape positioned at least partially in said gaps;a planar diaphragm operably attached to each said electric conductor means;and means for supporting said magnetized member, said pole pieces, said diaphragms and said electric conductor means.
25
Electromagnetic driving means for a planar acoustic transducer comprising:a magnetized member for creating a magnetic field;a first pole piece of magnetically conductive material adjoining a pole face of said magnetized member;a second pole piece of substantially U-shape adjoining the opposite pole face of said magnetized member and forming pairs of spaced apart elongated gaps with said first pole pieces, said, gaps containing regions of relatively high flux density in said magnetic field;electric conductor means of substantially coil shape positioned at least partially in said gaps and substantially parallel to magnetic flux lines of said magnetic field in said gaps;and means for supporting said electric conductor means.
27
Electromagnetic driving means for a planar acoustic transducer comprising:a magnetized member for creating a magnetic field and having a periphery;pole piieces of magnetically conductive material adjoining opposed pole faces of said magnetized member;other pole pieces for forming at least two pairs of spaced apart elongated gaps with said first mentioned pole pieces, said gaps containing regions of relatively high flux density in said magnetic field;and an electric conductor means of substantially coil shape positioned at least partially in one pair of said gaps, and means for supporting each said electric conductor means.
34
Electromagnetic driving means for a planar acoustic transducer comprising:a magnetized member for creating a magnetic field;pole pieces positioned adjacent the periphery for forming at least one pair of spaced apart elongated gaps with said magnetized member;said gaps containing regions of relatively high flux density;an electric conductor means of substantially coil shape positioned at least partially in each pair of said gaps and substantially parallel to magnetic flux lines of said magnetic field in said gaps;magnetically conductive material being interlaid with and insulated from said electric conductor means to increase magnetic flux lines of said magnetic fields traversing said electric conductor means;and means for supporting said electric conductor means and said magnetically conductive material.
35
Electromagnetic driving means for a planar acoustic transducer comprising:a magnetized member for creating a magnetic field;pole pieces positioned adjacent the periphery for forming at least one pair of spaced apart elongated gaps with said magnetized member;said gaps containing regions of relatively high flux density;an electric conductor means of substantially coil shape positioned at least partially in each pair of said gaps and substantially parallel to magnetic flux lines of said magnetic field in said gaps;and means for supporting said electric conductor means by essentially non-magnetized and resilient material positioned between said magnetized member and said electric conductor means.
36
An acoustic transducer comprising:at least one electromagnetic driving means;and at least one diaphragm operably attached to each said electromagnetic driving means and driven over a substantially large portion of its surface area by said electromagnetic driving means, each diaphragm being comprised of at least two membranes fastened adjacent their periphery and internally separated by strut members to a shallow lenticular form, whereby the two membranes operate as a low mass, highly responsive single diaphragm unit.
38
An acoustic transducer comprising:at least one electromagnetic driving means;and at least one dia- phragm operably attached to each said electromagnetic driving means and driven over a substantially large portion of its surface area by said electromagnetic driving means, each diaphragm being comprised of at least two membranes substantially sealed adjacent their periphery and separated by internal inflation to a shallow lenticular form, whereby the two membranes operate as a single diaphragm unit.
40
A diaphragm for an acoustic transducer comprising:at least two membranes fastened adjacent their periphery;and internal strut members capable of separating said membranes to a shallow lenticular form, whereby the two membranes operate as a low mass, highly responsive single diaphragm unit.
42
A diaphragm for an acoustic transducer comprising:at least two membranes fastened adjacent their periphery and capable of being internally inflated by pressure, and internal strut members capable of separating said membranes with said internal inflation to a shallow lenticular form, whereby the two membranes operate as a low mass, highly responsive single diaphragm unit.
43
A diaphragm for an acoustic transducer comprising:at least two membranes substantially sealed adjacent their periphery and capable of being internally inflated to a shallow lenticular form, whereby the two membranes operate as a single diaphragm unit.
45
An acoustic transducer comprising:at least one electromagnetic driving means, said electromagnetic means providing at least two independent electric conductor means;and at least one pair of substantially planar diaphragms positioned in substantially parallel array astride said electromagnetic driving means, each said diaphragm of said pair of diaphragms being operably attached for driving by an independent electric conductor means of said electromagnetic driving means.
47
An acoustic transducer comprising:at least one electromagnetic driving means;and at least one pair of substantially planar diaphragms operably attached to said electromagnetic driving means, each diaphragm of each pair of diaphragms being positioned substantially parallel to the other diaphragm of said pair of diaphragms and one of said diaphragms of each said pair of diaphragms being stiffened with at least one patch member capable of mechanically shifting the response of said diaphragm from the phase response of the other diaphragm of said pair of diaphragms.
49
A method of reproducing a stereophonic audio signal comprising the steps of:forming a pair of diaphragms, each diaphragm of said pair being substan3,873,784 tially parallel to the other diaphragm of said pair;and driving said diaphragms of said pair by separate channels of said stereophonic audio signal.
50
An acoustic transducer adapted for mounting on a wall comprising:at least one electromagnetic driving means and;at least three substantially planar diaphragms, each operably attached for driving by said electromagnetic driving means, and positioned substantially parallel to each other.
52
A method of reproducing an audio signal comprising the steps of:forming a plurality of spaced pairs of planar diaphragms with the volume contained between each pair of diaphragms substantially enclosed with each diaphragm of said pair substantially parallel to the other diaphragm of said pair;driving at least one of said pairs of diaphragms with said diaphragms motionally in-phase with low frequency audio signals;and driving at least one of said pairs of diagrams with said diaphragms motionally out-of-phase with middle and high frequency audio signals.
53
An electric driver means for a planar acoustic transducer comprising:sections of insulating backing of non-magnetically conductive material;and sections of conductive pathway pattern fixed to said sections of insulating backing and capable of being formed round the periphery of a magnetized member in a singular electric driver means.
56
A method of making a planar acoustic transducer comprising the steps of:adjoining pole pieces to opposed pole faces of a magnetized member having at least one substantially planar pole face;forming substantially spiral coil electric conductor means of a conductive pathway pattern;forming said electric conductor means round the periphery of said magnetized member and spaced from said magnetized member;positioning other pole pieces spaced from said electric conductor means and forming gaps with said first mentioned pole pieces;and operably attaching at least one diaphragm to said electric conductor means.

Independent claims28

307 paragraphs in 23 sections, as filed

[57] ABSTRACT

An acoustic transducer of planar shape. An electric conductor means of a coil, preferably flat spiral or flat helical configuration is operably attached to a diaphragm and positioned in the magnetic field of at least one magnetized member adjacent one of its pole faces. Magnetically conductive pole pieces preferably are positioned adjacent the magnetized member to form a dense elongated region of preferably substantially uniform magnetic flux density in said magnetic field where the electric conductor means is preferably located. Preferably said region in said magnetic field is contained in pairs of spaced apart elongated gaps formed by said pole pieces and one said magnetized member. A second diaphragm is preferably positioned adjacent the opposite pole face of one said magnetized member and preferably driven by a separate electricconductor means and the volume contained between said diaphragms is enclosed.

Claims, 43 Drawing Figures

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ACOUSTIC TRANSDUCER

This application is a continuation of then co-pending, now abandonded, application Ser. No. 887,557, filed Dec. 23, 1969, now abandoned.

This invention relates to an acoustic transducer of a planar shape. It is particularly useful in reproducing speech, music and other sounds with a quality associated with hi-fidelity sound reproduction in an inexpensive, dependable and widely adaptable way.

It is a physical fact that an electric current moving through an electric conductor means in a magnetic field normal to the direction of the lines of magnetic flux produces a force normal to the directions of the electric current and the magnetic flux lines (in accordance with the well-known “right-hand rule”). The electromagnetic acoustic transducer applies this principle to convert variations in electric current into corresponding variations in mechanical force and in turn physical displacement variations of a diaphragm, to produce acoustic waves with corresponding variations in frequency and intensity.'

I. The intensity of an acoustic wave is the time average rate at which energy is transported by the acoustic wave per unit area across a surface usually perpendicular, but possibly oblique; to the direction of propagation.

Loudspeaker development has been aimed at achieving, as far as possible, instantaneous and uniform response of the diaphragm when driven by a force at any acoustic frequency. Loudspeakers generally have been limited in the quality2 of acoustic waves and the range of audible frequencies which they could recreate. Difficulties have been particularly pronounced in the common conical loudspeaker.

2. The quality of sound reproduction is determined by the accuracy with which the frequencies of sound and their respective intensities can be recreated.

Acoustic transducers of a planar shape and driven by electrostatic forces are broadly old and well known. They have been used side by side in multiples to provide a planar loudspeaker of very large diaphragm area. Such planar acoustic transducers have had inherent operating advantages over the common full range conical loudspeaker: (i) They eliminate perceptible Doppler effect distortion of middle and high frequencies because of the relatively small displacement amplitude of a very large diaphragm at low frequencies, (ii) They do not exhibit the characteristic “rim resonance” of conical loudspeakers and therefore provide a smoother transition in reproduction from low-frequency to midfrequency sounds, (iii) They provide low frequency reproduction of greater intensity because of the movement of a relatively very large diaphragm through a comparatively small displacement amplitude to reproduce such low frequencies. But such planar transducers utilizing electrostatic driving means are very expensive to build and sensitive to acoustical overloads and inefficient. Such transducers were not to my knowledge heretofore commercially made with electromagnetic driving means moving the diaphragm.

I have presented one way of overcoming these disadvantages and difficulties in my copending application Ser. No. 784,669, filed Dec. 18, 1969, now U.S. Pat. No. 3,651,283. The present invention overcomes these disadvantages and difficulties in another way. It makes the use of an acoustic transducer of a planar shape driven by electromagnetic driving forces commercially feasible with sound reproducing apparatus of hi-fidelity grade. Moreover, it provides a versatility and decora2 tiveness in the design, application and installation of planar acoustic transducers heretofore unseen in the art, and it makes planar acoustic transducers commercially competitive with conical loudspeakers.

provide an acoustic transducer of planar shape having at least one electromagnetic driving means and at least one diaphragm operably attached thereto. The electromagnetic driving means is comprised of at least one magnetized member and at least one electric driver means. Each magnetized member creates a magnetic field and has at least one substantially planar pole face. Each electric driver means is comprised of at least one electric conductor means and possibly in addition, a conductor forming means to support the electric conductor means and operably attach it to the diaphragm. Each electric conductor means is substantially in coil form, preferably in flat configuration, and is spaced from one said planar pole face. Each electric conductor means is positioned in the magnetic field of said magnetized member and in some embodiments preferably forms a plane substantially parallel to at least one said planar pole face. At least one essentially nonmagnetic diaphragm, preferably of planar shape, is operably attached to at least one said electric conductor means or conductor forming means, and preferably forms a plane substantially parallel to, and spaced from, at least one said planar pole face.

I prefer that each acoustic transducer unit contain only one magnetized member, although a plurality of magnetized members can be used (see FIGS. 7,8,9,12,13 and 14). Each magnetized member may be an electromagnet or a permanent magnet. I prefer, however, that each magnetized member be a permanent magnet because of the avoidance of magnetizing coils and additional electric power requirement and because its magnetic field is substantially stable and fixed, i.e., the magnetic field will not fluctuate to any substantial degree during operation of the transducer. Further, the fabrication of permanent magnets is less costly than the fabrication of electromagnets of comparable field strength.

When the magnetized members are permanent magnets the dimensions and shape of the magnetized member are critical with respect to obtaining maximum magnetic efficiency from the magnetized members, but are not limiting except as hereinafter preferred. They will vary with the material used to make magnetized members and the shapes and relations of the other elements of a particular embodiment to the magnetized members. The magnetized members may, for example, be rectilinear or curvilinear in cross-section. I prefer that the magnetized members have a large pole face area to thickness ratio. A large ratio of pole face area to magnet thickness provides for a thinner embodiment of the planar transducer, as well as a larger area of the diaphragm that can be driven directly by the electric conductor means attached thereto. The ratio cannot however be enlarged without limit because the density of the magnetic field produced will be diminished as the thickness is reduced beyond a point, or as the pole face area is increased beyond a point. The optimum ratio will vary with the material used to make the magnetized members and the shapes and relations of the other elements of the particular embodiment to the magnetized members. Such permanent magnets can, for example, be made of an alloy of iron, nickel, aluminum, or cobalt. I prefer, however, that sintered ferrite

3,873,784 material be used because I have found that it can provide a permanent magnet of a given magnetic strength that has a larger pole face area to thickness ratio than most metallic alloys.

I contemplate that the planar pole faces of the mag- 5 netized members be as nearly flat as practicable. The shape of said pole faces may however be varied to produce a stronger and more uniform magnetic field in the region where the electric conductor means is located. Said planar pole face may, for example, be curvilinear 10 in shape, (see FIG. 17). The periphery of the pole faces may be in any advantageous configuration, e.g. circles, elipses, rectangles, irregular curves. 1 prefer that the configuration of the periphery be a rectangle or the like where the periphery is large for a given surface area. In 15 this way, the reproductive quality of the transducer is improved and the efficiency increased.

The positioning of the electric conductor means relative to the magnetized member is critical but not limiting. The essential feature is that the electric conductor 20 means be positioned in the magnetic field of the magnetized member. In addition, the electric conductor means should be positioned in said magnetic field in such a way that the regions of the magnetic field in which the electric conductor means are positioned are 25 substantially uniform and in turn, the forces exerted on the diaphragm are substantially symmetrical with regard to movement of the electric conductor means from a fixed point in opposing directions. In this way, the diaphragm will not pitch or yaw to any significant 30 degree and thereby produce audibly spurious acoustic waves. The symmetry of the positioning can be accomplished by varying the magnetic field, or by varying the number of turns or spacing between turns of the electric conductor means. If the electric conductor means 35 is positioned in said magnetic field in such a way that the regions in which it is located are not substantially uniform, the support means for the diaphragm should be adjusted, or some other compensating means used so that the diaphragm does not pitch or yaw. 40

Preferably, the electric conductor means is positioned and moved within regions of said magnetic field that are of substantially constant magnetic flux density. In this way, electric current conducted through said electric conductor means causes responsive and sub- 45 stantially uniform linear forces to be exerted on the diaphragm at any given frequency. I have found that (where pole pieces are not used, see infra, p. 10) the electric conductor mmeans should be positioned close to one planar pole face of the magnetized means, yet spaced from it a distance necessary to allow clearance between the planar pole face and the electric conductor means during operation of the transducer.

The electric conductor means can be made by mechanically winding or sewing a coil configuration di- 55 rectly onto a diaphragm, or can be made by mechanically winding a spiral and/or helical coil configuration on a conductor forming means. I prefer that the configuration of the coil be flat. In addition, I prefer that the „ coil be one continuous winding; it can however be multiple (i.e., discontinuous) and spaced spiral or helical configurations of varied design that are woven into, sewn to, or otherwise fastened to the diaphragm or the conductor forming means. 65

The electric conductor means is preferably made of material which is highly electrically conductive (i.e., low resistance) but essentially non-magnetizable, such as copper, aluminum and silver wire. Further, I prefer that the electric conductor means be made of conductive pathway patterns such as those formed by printed circuit, printed wiring or pressed wiring methods; use of such manufacturing methods permits the production of low cost and high quality electric! conductor means.

In addition, I contemplate that interlaid with and insulated from the electric conductor means can be magnetically conductive material such as iron or iron alloy. They should be interlaid generally in the plane traversed by the magnetic flux lines through the electric conductor means. By this arrangement, the magnetic lines of flux of the magnetic field created by the magnetized member will tend to concentrate in the region where the electric conductor means is moving and thereby increase the efficiency of the acoustic transducer.

The diaphragm is fastened to said electric conductor means and itself supported so that the electromagnetic driving means displaces the diaphragm when current passes through the electric conductor means. The diaphragm is of an essentially non-magnetizable material such as paper, resins, rubbers, metal foil, plasticized paper, metallic paper or treated or untreated textiles. The diaphragm should be relatively thin and of small mass so that it is very sensitive to displacement by minute electromagnetic driving forces. The surface portions of the diaphragm may be of any suitable shape and may even conform to the decor of the listening room or of sound reproduction system housing in which the acoustic transducer is used.

Preferably, the diaphragm is of a membrane-like shape and is driven over a substantially large portion of its surface area. Such membranous diaphragms are of small mass and low cost and are easily fabricated. I prefer that such diaphragms be made of material of long term stability and high flexibility but low elasticity, such as varnished cambric, and be placed under tension over a supporting frame. Such membranous diaphragms permit more accurate response to audio signals than do relatively heavy and relatively stiff speaker cones and do not exhibit the “rim resonance” of speaker cones, thereby improving the transition between sounds of differing frequency. They also can be made to generate less harmonic distortion of the sound reproduction than do stiff speaker cones.

The membranous diaphragm can be driven over a substantially large portion of its area by reason of the configuration of the electric conductor means and/or the configuration of conductor forming means and the way they are attached to the diaphragm. Alternatively or supplementally this can be accomplished by stiffening the diaphragm by painting or spraying the diaphragm over a substantially large portion of its area with materials such as certain epoxy and polyester liquid resins that solidify in place on curing, or by overlaying a portion of the membranous diaphragm with light weight plastic or textile patches. Alternatively the diaphragm can be comprised of two membranes pneumatically sealed around the edges and/or at intermediate points and separated by internal strut members. Preferably the diaphragm is inflated under pressure to a shallow lenticular form either with or without internal strut members. In this way, the membranous diaphragm can be made sufficiently stiff to respond to the forces exerted by the electric conductor means over substantially its entire surface area and still be light and com3,873,784 pliant enough to be sensitive to very small forces exerted by the electric conductor means. These conditions are compromised when the diaphragm is sprayed or painted with stiffening material or overlaid with stiffening members. In addition, 1 have found that inflation of the diaphragm increases the efficiency of the transducer.

The diaphragm may be supported by either rigid or flexible means. If rigid support means are used, the diaphragm should be under tension or have adequate compliance to restore itself to its original position when it is displaced by the electromagnetic driving means. If flexible support means are used, the support means should have compliance for returning the diaphragm to its original position when it is displaced by the electromagnetic driving means. I prefer that such support means be structural materials that are essentially non-magnetizable such as wood, molded and/or reinforced plastics, aluminum, brass, etc. Furthermore, I have found that the diaphragm (along with the electric conductor means) can be supported by essentially non-magnetizable, compliant material positioned on any planar pole face of said magnetized member.

The electric conductor means, conductor forming means (if any), and diaphragm is sometimes called the “mobile assembly.” The mobile assembly as a whole is preferably of small mass, especially where response to a high frequency signal is desired.

I prefer that pole pieces be positioned adjacent the periphery of the magnetized member to direct and intensify the magnetic field by providing a low reluctance path for the magnetic flux from one pole face of the magnetized member to the conjugate pole face of the magnetized member. The pole pieces may be made of any magnetically permeable material. Preferably the pole pieces are made of material having high magnetic permeability and low magnetic retentivity such as “soft” iron and low carbon steel. The pole pieces may be laminated to reduce eddy-current effects. The pole pieces can be of any suitable geometric shape that is appropriate to direct and intensify the magnetic flux of said magnetic field in the region where the electric conductor means is located, and in addition, make said magnetic field preferably substantially symmetrical and preferably uniform in the region where the electric conductor means is located. One form of pole piece can be used that is of a substantially U-shaped and adjoins the opposite pole face from the planar pole face. The pole pieces may be independently supported or may be supported by the magnetized member through spacer members of essentially non-magnetizable material, i.e., any material that is substantially inert to a magnetic field such as plastics and other materials showing high magnetic reluctance.

Preferably the pole pieces are positioned adjacent the periphery of the magnetized member to form pairs of spaced apart elongated gaps with one said magnetized member or other pole pieces, said gaps containing regions of relatively high magnetic flux density. The regions of said magnetic field contained in said gaps preferably approach substantially linear and symmetrical magnetic flux density. And the electric conductor means are positioned and, in operation, moved within said regions of substantially linear and symmetrical magnetic flux density in said gaps. By this arrangement, the forces exerted on the diaphragm by the electric driver means at any given frequency are substantially constant and thereby limit distortion of the audio signal in reproduction.

In addition, said gaps containing the magnetic fields should be adjusted within narrow limits. Said gaps should be as narrow as possible to produce magnetic flux of highest density and to approach a substantially constant magnetic flux density in said gaps. Yet, said gaps should be sufficiently broad so that a slight change of the electric conductor means, the pole pieces, or magnetized member does not cause the electric driver means to bind or scrape in said gaps. In this way, electric current conducted through said electric conductor means causes highly responsive and substantially uniform linear forces to be exerted on the electric driver means positioned in said gaps at any given frequency.

I contemplate, in addition, that a substantial portion of said gaps may be filled with resilient, essentially non-magnetizable material, such as highly compliant rubber or foam resin, to support the electric conductor means, to preserve accurate alignment of the parts, and to improve the ruggedness of the electromagnetic driving means during mounting. Such resilient essentially non-magnetizable material should be thermally conductive to aid in dissipating whatever heat is generated from the passage of electric current through the electric conductor means. By this arrangement, electromagnetic driving means can be made separately as intermediate assemblies, and can be disposed geometrically or preferably randomly over any mounting surface and covered with a single diaphragm or sections of diaphragm to form an acoustic transducer.

I prefer that the electric conductor means be of a substantially flat, coil configuration. Such electric conductor means can be (i) of a spiral configuration and form a plane that is substantially parallel to the flux lines of said magnetic field in said gaps or (ii) of a helical configuration and substantially perpendicular to flux lines of said magnetic field in said gaps.

The pole pieces can be a first pole piece adjoining a pole face of said magnetized member and a second pole piece of substantially U-shape adjoining the opposite pole face of said magnetized member. The spaced apart elongated gaps containing substantially linear and symmetrical regions of relatively high flux density are thereby formed between said first pole piece and said second pole pieces. In the alternative, the pole pieces can be first pole pieces of magnetically conductive material adjoining both faces of the magnetized member and second pole pieces spaced from the periphery of said magnetized member. Said second pole pieces can be independently supported, or supported by the magnetized member through spacer members of essentially non-magnetized material. By the latter means, one or two pairs of spaced apart elongated gaps containing substantially linear and symmetrical regions of relatively high flux density are formed between said first pole piece and said second pole piece, depending on the geometry and positioning of the spacer member relative to said first and second pole pieces. By these arrangements, where the pole pieces adjoin the pole faces, the magnetic flux density of regions of the magnetic fields in said gaps are intensified and approach closer uniformity.

I further prefer that the electric conductor means drive two diaphragms positioned substantially parallel to each other on opposite sides of the magnetized member. The electric conductor means can be one means

3,873,784 driving both diaphragms (see FIGS. 37,38 and 39); but for operational purposes, I prefer two separate electric conductor means to drive the diaphragms independently. The electric driver means is preferably substantially symmetrical about the center lines of the magnetized member.

The applications for two-diaphragm planar acoustic transducers are varied. The separate electric conductor means may be driven independently, as in the case of stereophonic audio signals, or they may be driven outof-phase by any phase displacement up to 180°. In addition, two diaphragms increase the transient response, the linearity of motion with regard to the amplitude of the audio signal, the damping, and the efficiency of such acoustic transducers.

Furthermore, by this arrangement the effects caused by moving either one of the two electric conductor means through a non-linear region of the magnetic field of the magnetized member can be reduced to a negligible factor because the sound produced is the resultant of both diaphragms. As inferred earlier, herein when the electric conductor means carrying a current is caused to move through regions of varying magnetic flux density, the forces exerted on the diaphragm by the electromagnetic driving means varies and in turn results in the reproduction of distorted sounds; In the acoustic transducer having one diaphragm, I therefore emphasized that the magnetic flux density should be substantially uniform in the region of the magnetic field in which the electric conductor means is moved. However, in the acoustic transducer having two diaphragms and driven by two independent electric conductor means, the electric conductor means can be arranged and driven electrically so that one electric conductor means is moving into a region of high magnetic flux density while the other is moving into a region of low magnetic flux density. In this way, a substantial equality of the resultant forces exerted on the diaphragms are preserved, and in turn the distortion of the sounds reproduced limited, if not eliminated. The concern is therefore not with the uniformity of the regions of the magnetic field through which the electric conductor means move, but rather with the symmetry of the regions of the magnetic field through which the two electric conductor means move.

Preferably, the space between the two diaphragms is enclosed or otherwise separated from the exterior ambience by enclosure means. This can be done by structural members and/or frame-like supporting members for the diaphragms. Small vent holes should be provided in the enclosure means to permit compensation for changes in atmospheric pressure. Further, it may be desirable in some embodiments to provide larger openings, e.g., slots, in the enclosure means to provide partial relief of the air pressure within the volume contained by the enclosure means and diaphragms to improve the acoustic response of the transducer by introducing such acoustic resistance. 1 prefer however that the enclosure means substantially seal-off the volume 6θ enclosed by the enclosure means and the diaphragms from the exterior ambience except for the small vent holes. By use of the latter arrangement, I have found that when the electromagnetic driving means is operated so that the two diaphragms are motionally in phase, (i.e., when they physically move in the same direction at the same time powered by the same electrical signal), the bass response is improved. On the other hand, when the diaphragms are operated motionally out-of-phase the bass responses are essentially suppressed and the middle frequency and high frequency responses are more prominent. These results are be5 lieved due to the volume of air contained by the enclosure means being relatively small compared to the exterior ambience and its compressibility low compared to the compressibility of the exterior ambience. As a result, the entrapped air acts as a substantially stiff meld dium mechanically linking the internal surfaces of the diaphragms and therby causes each diaphragm to act as a motional control on the other. This allows for an amplification of the response from the diaphragm at low frequencies and a heavy damping of spurious motion of 15 the diaphragms. In addition, it permits compensation for acoustic distortions and imperfections caused by the variations in assembly tolerances of the various elements of the transducer by slightly shifting the phase of motion of the two diaphragms either electrically or me20 chanically by slightly weighting one of the two diaphragms.

An acoustic transducer installation comprising a number of my two diaphragm acoustic transducers within an enclosure means can be connected electri25 cally so that some of them have their two diaphragms motionally in-phase and are provided with a simple low-pass filter to reproduce principally low frequencies, while the remaining acoustic transducers of a given array are electrically connected so that their op30 positely disposed diaphragms are motionally out-ofphase. By this arrangement favorable differences of overall sound reproduction can be achieved at various frequencies without the use of expensive and complex electrical crossover networks or separate amplifiers. In 33 addition, I have found to my surprise that the two diaphragms can be driven by the separate channels of a stereophonic recording either in-phase or out-of-phase with negligible change in mid-frequency and highfrequency reproduction, and with no perceptible 0 change in low-frequency reproduction. This is unexpected: The effect of reversing the phase relation of the two diaphragms while reproducing a monophonic recording results in cancellation of low frequency sounds and unpleasant distortions of mid-frequency and highfrequency sounds, as would be expected with the small air volume of relatively low compressibility contained between the diaphragms. The stereophonic arrangement however corresponds in effect to an acoustic monopole — a condition theretofore not realized in commercial practice to my knowledge.

contemplate that the total displacement amplitude of the diaphragm of my acoustic transducer be small (e.g., 0.0005 to 0.2500 inch) so that the Doppler-effect distortion (FM modulation) will be small. In application, my acoustic transducers may be assembled in multiples so that a very large area of diaphragm exposed to the ambient air of a listening room may be driven uniformly by the electromagnetic driving means. Therefore, the acoustic transducer need not be mounted in a horn or an acoustically sealed or “tuned” enclosure (as a conical loudspeaker often needs to be) to radiate wide range sound reproduction into a listening area, even though the average intensity of the sound recreated by a given area of the acoustic transducer is low. In addition, my acoustic transducers can be mounted in a stacked array to adapt the assembly for mounting on a wall; this arrangement reduces the effect of the high

3,873,784 resistance to compressibility of an enclosed air volume by moving diaphragms in-phase.

Other details, objects and advantages of my invention will become apparent as the following description of the present preferred embodiment proceeds. 5

In the accompanying drawings I illustrate presently preferred embodiments of my invention in which:

FIG. 1 is a partial top view of a planar acoustic transducer;

FIG. 2 is the partial cross-sectional view of the planar 10 acoustic transducer shown in FIG. 1 taken along line II-II;

FIG. 3 is a top view of a planar acoustic transducer;

FIG. 4 is a cross-sectional view of the acoustic transducer shown in FIG. 3 taken along line IV—IV; 15

FIG. 5 is a response curve comparing the operation of the acoustic transducer herein described and shown in FIGS. 3 and 4 with various “tweeter” type loudspeakers;

FIG. 6 is a partial cross-sectional view of a planar 20 acoustic transducer;

FIG. 7 is a partial top view with portions broken away of a planar acoustic transducer;

FIG. 8 is a partial cross-sectional view of the acoustic transducer shown in FIG. 7 taken along line VIII—VIII; 25

FIG. 9 is a partial top view of a planar acoustic transducer;

FIG. 10 is a partial cross-sectional view of the acoustic transducer shown in FIG. 9 taken along line X—X;

FIG. 11 is a response curve comparing the operation 30 of the acoustic transducer herein described and shown in FIGS. 9 and 10 with a good quality 8 inch conical loudspeaker;

FIG. 12 is a partial exploded perspective view of a planar acoustic transducer; 35

FIG. 13 is a partial top view of the acoustic transducer shown in FIG. 12;

FIG. 14 is a partial cross-sectional view of the acoustic transducer shown in FIGS. 12 and 13.

FIG. 15 is a partial top view of a planar acoustic 40 transducer;

FIG. 16 is a partial cross-sectional view of the planar acoustic transducer shown in FIG. 15 taken along line XVI—XVI;

FIG. 17 is a partial cross-sectional view of a planar 45 acoustic transducer;

FIG. 18 is a cross-sectional view of a planar acoustic transducer;

FIG. 19 is a top view of a planar acoustic transducer;

FIG. 20 is a cross-sectional view of the acoustic transducer shown in FIG. 19 taken along line XX—XX;

FIG. 21 is a partial cross-sectional view of a planar acoustic transducer showing the interlaying of magnetically conductive material with the electric conductor means;

FIG. 22 is a partial top view of a planar acoustic transducer;

FIG. 23 is a partial cross-sectional view of the planar acoustic transducer shown in FIG. 22 taken along line XXIII—XXIII;

FIG. 24 is a partial top view with portions broken away of a planar acoustic transducer;

FIG. 25 is a partial cross-sectional view of the planar acoustic transducer shown in FIG. 24 taken along line XXV-XXV;

FIG. 26 is a partial top view with portions broken away of a planar acoustic transducer;

FIG. 27 is a partial cross-sectional view of the acoustic transducer shown in FIG. 26 taken along line

XXVII-XXVII;

FIG. 28 is a partial cross-sectional view of an alternative embodiment of the planar transducer shown in FIG. 26 taken along line XXVII—XXVII;

FIG. 29 is a partial cross-sectional view of an alternative embodiment of the planar transducer shown in FIG. 26 taken along line XXVII—XXVII;

FIG. 30 is a partial cross-sectional view of an alternative embodiment of the planar transducer shown in FIG. 26 taken along line XXVII—XXVII;

FIG. 31 is a partial cross-sectional view of an alternative embodiment of the planar transducer shown in FIG. 26 taken along line XXVII—XXVII;

FIG. 32 is a partial cross-sectional view of an alternative embodiment of the planar transducer shown in FIG. 26 taken along line XXVII—XXVII;

FIG. 33 are response curves comparing the operation of the acoustic transducers herein described and shown in FIGS. 15, 16, 26 and 30 with a good quality 8 inch conical loudspeaker;

FIG. 34 is a partial top view with portions broken away of a planar acoustic transducer;

FIG. 35 is a partial cross-sectional view of the planar acoustic transducer shown in FIG. 34 taken along line XXXV-XXXV;

FIG. 36 is a partial top view with portions broken away of an alternative embodiment of the planar transducer shown in FIG. 35;

FIG. 37 is'a partial cross-sectional view of a planar acoustic transducer particularly adaptable for use in automobiles;

FIG. 38 is a partial cross-sectional view of a planar acoustic transducer;

FIG. 39 is a developed view of the electric driver means for the acoustic transducer shown in FIG. 38;

FIG. 40 is a perspective view of the electric driver means for the planar acoustic transducer shown in FIG. 38;

FIG. 41 is a perspective view with portions broken away of a four-modular array of planar acoustic transducers as shown in FIGS. 15 and 16;

FIG. 42 is a cross-sectional view of a modular array of planar acoustic transducers as shown in FIGS. 15 and 16 particularly adapted for mounting on a wall; and

FIG. 43 are response curves comparing the operating of an eight-modular array of planar acoustic transducers shown in FIGS. 15, 16, 26, 30 and 41 with a good quality 8 inch conical loudspeaker and a good quality bass reflex system.

Referring specifically to the drawings and particularly FIGS. 1 and 2 thereon, an acoustic transducer has an electromagnetic driving means 2 and a diaphragm 3 operably attached thereto. The electromagnetic driving means 2 is comprised of a magnetized member 5 and an electric driver means 4. The magnetized member 5 creates a magnetic field 6 and has a planar North pole face 7 and a South pole face 8. The magnetized member 5 may be positioned on a base member of magnetically conductive or essentially non-magnetically conductive material (not shown), or may be positioned in a frame of essentially non-magnetically conductive material adjoining the periphery of the magnetized member 5 (not shown). The electric driver means 4 is comprised of electric conductor means 9 of a substantially flat spiral coil configuration attached directly to and

3,873,784 supported by said diaphragm 3. The electric conductor means 9 is positioned in said magnetic field 6 and forms a plane substantially parallel to and spaced from said planar pole face North 7 at a distance just sufficient to allow clearance between the planar North pole face 7 and the electric conductor means 9 during operation of the acoustic transducer. The diaphragm 3 may be supported by essentially non-magnetically conductive and resilient material, such as foam resin or rubber, in the space 10 between the planar North pole face 7 of magnetized member 5 and the diaphragm 3 and electric conductor means 9 (not shown), or may be supported under tension by a frame structure of essentially nonmagnetically conductive material adjacent the periphery of the magnetized member 5 (not shown). In either case, the diaphragm 3 is a membranous material, for example, varnished cambric, and forms a plane substantially parallel to the planar North pole face 7.

I believe that the operation of this embodiment is due not simply to the usual electromagnetic forces in accordance with the well known “right-hand rule.” The magnetic lines of flux “seen” by the North pole face 7 of the magnetized member 5 emanating from the conjugate South pole face 8 are apparently relatively weak compared to the centralized resultant electromagnetic field created by the audio signal flowing through the electric conductor means 9. The alternating audio signal flowing through the electric conductor means 9 produces a resultant alternating magnetic field about the electric conductor means 9. The North pole face 7 of the magnetized member 5 “sees” essentially the concentrated portion of the alternating magnetic field in the space 10 created by the audio signal flowing through electric conductor means 9 and thereby exerts alternating attractive or repulsive forces on the electric conductor means 9. Opposing forces are exerted by reason of said alternating magnetic field on the obverse side of the electric conductor means 9, but they are of much less magnitude because of the greater distance of the south magnetic field from the North pole face 7 and of their lesser density. The alternating forces exerted by the magnetized member 5 in turn causes a motional excursion of the diaphragm 3 in the general direction indicated by the double-headed arrow in FIG. 2, although motional excursions in angular directions are also caused by the curving of the magnetic flux lines of magnetic field 6 as shown in FIG. 2.

Another planar acoustic transducer is shown in FIGS. 3 and 4. The electromagnetic driving means 11 is comprised of a magnetized member 12 and an electric driver means 13. The magnetized member 12 creates a magnetic field 14 and has a North pole face 15 of planar shape. Said magnetized member 12 is supported by pole piece 16. Pole piece 16 is substantially U-shaped, and adjoins South pole face 17 and is spaced from the periphery of magnetized member 12. Electric driver means 13 is comprised of electric conductor means 18 having a substantially flat spiral coil shape positioned in said magnetic field 14 created by said magnetized member 12 and substantially parallel to and spaced from said North pole face 15. Said electric conductor means 18 is operably attached to diaphragm 19. Electrical conductor means 18 and diaphragm 19 are supported by non-magnetically conductive and resilient material 20 on North pole face 15 of magnetized member 12.

By this arrangement, the pole piece 16 intensifies said magnetic field 14 by conducting the southpolarized magnetic flux lines along a much lower reluctance path than air into proximity of the North pole 5 face 15, and gives the magnetic flux lines parabola-like configurations that spread them over the region 21 where they intersect electric conductor means 18. The forces exerted on the diaphragm 19 are in turn stronger and result in a more efficient acoustic transducer than 10 the acoustic transducer shown in FIGS. 1 and 2. The operations of this embodiment are believed more in accord with well known electromagnetic principles than the transducer shown in FIGS. 1 and 2.

The acoustic transducer above described and shown 15 in FIGS. 3 and 4 is particularly suited for the reproduction of high-frequency sounds. Such transducers are known in the trade as “tweeters.” To illustrate the merit of this acoustic transducer, I have compared it with other tweeters over their useful range from about 20 1,000 cycles per second to about 12,000 cycles per second. The results are shown in FIG. 5. Curve A is my acoustic transducer with an approximately 11 square inches of diaphragm area made of sheet “Mylar,” and about 4.5 X 2 inches rectangular, spiral electric con25 ductor means 18 having 20 turns, a rectangular magnetized member 12 of sintered ferrite, 4.5 in. X 2 in. X 0.5 in., and the resilient material 20 having a thickness of 3/32 inches. Curve B is a good quality horn tweeter. Curve C is a low price cone tweeter model. And Curve 30 D is a medium price horn tweeter. The performance of each tweeter was measured in free-field, with the same substantially constant power input to its electric conductor means, and the same microphone placement relative to the tweeter. As can be readily seen from 35 FIG. 5, my acoustic transducer gives a much more uniform intensity level3 over the useful frequency range than do any of the tweeters tested.

3. The intensity level B of a sound wave is defined by the equation: B—10 log 1,/1, where /, is the intensity and lz is a reference intensity taken as IO-,li watt/cm2, corresponding roughly to the faintest sound 40 which can be heard. Intensity levels are expressed in decibels, abbreviated db.

Another planar acoustic transducer is shown in FIG. 6 which has the same elements and arrangement of elements as FIGS. 1 and 2 except for the following varia4j tions and additions. The electric conductor means 9' is operably attached to the opposite side of the diaphragm 3', which does not affect the operation of the planar acoustic transducer. The electromagnetic driving means 2' is comprised, in addition, of a second sep50 arate electric driver means 22, and the magnetized member 5' has in addition South pole face 8' of planar shape. The electric driver means 22 is comprised of electric conductor means 23 of a substantially flat spiral coil configuration. The electric conductor means 23 55 is positioned substantially parallel to and spaced from the planar South pole face 8', and is operably attached to and supported by diaphragm 24. The diaphragm 24 may be supported by essentially non-magnetically conductive and resilient material in space 25 between the ¢0 planar South pole face 8' of magnetized member 5' and the diaphragm 24 (not shown), or may be separately or jointly supported under tension by frame structure of essentially non-magnetically conductive material adjacent the periphery of the magnetized member 5' (not 65 shown). In any case, diaphragm 24 is a membranous material, for example varnished cambric, and forms a plane substantially parallel to the planar South pole face 8' and substantially parallel to the diaphragm 3'.

3,873,784

The operation of the transducer shown in FIG. 6 is believed to be essentially the same as that described with respect to FIGS. 1 and 2, but the efficiency and damping characteristics of the acoustic transducer are bettered by taking advantage of both pole faces of the magnetized member 5'. In addition, the application for this embodiment is varied. The electric conductor means 9' and 25 may be driven independently as for example by the separate channels of a stereophonic audio recording, or they may be driven out-of-phase by any phase angle from 0° to 180° — produced electrically or mechanically.

Still another planar acoustic transducer is shown in FIGS. 7 and 8. The electromagnetic driving means 26 is comprised of magnetized members 27, 28 and 29 and an electric driver means 30. The magnetized members 27,28 and 29 are spaced from each other to form a pair of spaced apart elongated gaps 31 and 32 and have North pole faces 33, 34 and 35 respectively of planar shape and have South pole faces 36, 37 and 38 respectively of planar shape. The magnetized members 27, 28 and 29 have their oppositely polarized pole faces disposed adjacent each other to create elongated magnetic fields 39 and 40 in the regions 41, 42, 43 and 44 substantially outside the gaps 31 and 32 as shown in FIG. 8. Electric driver means 30 is comprised of two independent electric conductor means 45 and 46 of substantially flat rectangular spiral coil configurations and are attached directly to and supported by diaphragms 47 and 48 respectively. The electric conductor means 45 and 46 are positioned in said magnetic fields 39 and 40 and form planes substantially parallel to and spaced from said planar pole faces 34, 36 and 38, and 33, 35 and 37 respectively, and are positioned substantially parallel to each other. The diaphragms 47 and 48 are spaced from and positioned substantially parallel to pole faces 34, 36 and 38, and pole faces 33, 35 and 37, respectively, and are positioned parallel to each other. The diaphragms 47 and 48 may be separately supported by essentially non-magnetically conductive and resilient material in the spaces 49 and 50 respectively between the magnetized members 27, 28 and 29 and diaphragms 47 and 48 (not shown), or may be separately or jointly supported under tension by frame structure of essentially non-magnetically conductive material adjacent the periphery formed by the magnetized members 27, 28 and 29. In either case, diaphragms 47 and 48 are membranous material such as varnished cambric.

believe that the operation of this embodiment is due essentially to the well known electromagnetic forces in accordance with the right-hand rule. The flux densities of the magnetic fields 39 and 40 in the regions 41, 42, 43 and 44 are apparently predominant compared to the centralized resultant electromagnetic field created by the audio signal flowing through the electric conductor means 45 and 46. The mechanical forces exerted on the diaphragms 47 and 48 will cause an excursion substantially in directions shown by the double-headed arrows on FIG. 8, the direction of which will depend on the direction of the current flow through the electric conductor means 45 and 46.

This embodiment has the advantages of the two diaphragm acoustic transducer as hereinbefore described and provides a comparatively high intensity reproduction because of the relatively high flux density of the magnetic fields 39 and 40. It does, however, have the drawbacks (i) of being more costly than other planar acoustic transducers herein described, and (ii) of comparatively greater weight because of the plurality of magnetized members.

Another planar acoustic transducer is shown in FIGS. 9 and 10. The electromagnetic driving means 51 is comprised of magnetized members 52, 53 and 54, and an electric driver means 55. The magnetized members 52,53 and 54 are spaced from each other to form a pair of spaced apart elongated gaps 56 and 57 and have North pole faces 58, 59 and 60, respectively, of planar shape and have South pole faces 61, 62 and 63, respectively, of planar shape. The magnetized members 52, 53 and 54 have their oppositely polarized pole faces disposed adjacent each other to create elongated magnetic dields 64, 65, 66 and 67 in the regions 68, 69, 70, 71,72, 73, 74 and 75 substantially outside the gaps 56 and 57 as shown in FIG. 10. Electric driver means 51 is comprised of four independent electric conductor means 76, 77, 78 and 79 of substantially flat rectangular spiral coil configuration and are attached directly to and supported by diaphragms 80 and 81. The electric conductor means 76, 77, 78 and 79 are positioned in said magnetic fields 64, 65, 66 and 67 and form planes substantially parallel to and spaced from said planar pole faces 58, 59, 60, 61, 62 and 63. The electric conductor means 76 and 78 are positioned substantially parallel to each other and the electric conductor means 77 and 79 are positioned substantially parallel to each other. The diaphragms 80 and 81 are spaced from, and positioned substantially parallel to, pole faces 59, 61 and 63, and pole faces 58, 60 and 62, respectively, and are positioned substantially parallel to each other. The diaphragms 80 and 81 may be separately supported by essentially non-magnetically conductive and resilient material in the spaces 82 and 83, respectively, between the magnetized members 52, 53 and 54 and the diaphragms 80 and 81 (not shown), or may be separately or jointly supported under tension by a frame structure of essentially non-magnetically conductive material adjacent the periphery formed by magnetized members 52,53 and 54. In either case, the diaphragms 80 and 81 are membranous material for example varnished cambric.

The acoustic transducer shown in FIGS. 9 and 10 is believed to operate in essentially the same manner as the acoustic transducer shown in FIGS. 7 and 8 in accordance with the well known electromagnetic principles expressed by the right-hand rule. This embodiment, however, employs two electric conductor means 76 and 77 operably attached to diaphragm 80, and two electric conductor means 78 and 79 operably attached to diaphragm 81 to increase the efficiency of the acoustic transducer by taking greater advantage of the magnetic fields created by the magnetized members 52, 53 and 54. But it does have the same drawbacks noted above for FIGS. 7 and 8.

It should be noted that the magnetic flux density is different in the regions 70, 71, 72 and 73 where the flow of magnetic flux is between oppositely polarized faces of different magnetic members from where the flow of magnetic flux is between oppositely polarized faces of the same magnetized members. The positions, therefore, of electric conductor means 76, 77, 78 and 79 positioned in regions 70, 71, 72 and 73, respectively, are spaced apart more widely than the positions of electric conductor means 76, 77, 78 and 79 posi3,873,784 tioned in regions 68, 74, 69 and 75, respectively, to compensate for the difference in flux density of the various regions and thereby distribute the mechanical forces exerted on the diaphragms 80 and 81 more uniformly over the surface area thereof. This, of course, presumes that the current flow in electric conductor means 76 and 77 is substantially the same and the current flow in electric conductor means 78 and 79 is substantially the same.

The acoustic transducer above described and shown in FIGS. 9 and 10 is suited for the reproduction of full range sounds. To illustrate the merit of this acoustic transducer, I have compared it with a conical loudspeaker over the range of acoustic frequencies, i.e., from about 30 cycles per second to about 10,000 cycles per second. The results are shown in FIG. 11. Curve A is my acoustic transducer with approximately 120 square inches diaphragm areas 80 and 81 made of varnished cambric, about 5 in. X 3.5 in. outside dimension electric conductor means 76, 77, 78 and 79 having 22 turns each and diaphragms 80 and 81 supported by frame structure positioned around the periphery of the magnetized members 52, 53 and 54. Curve B is a good quality 8 inch loudspeaker. The performance of each transducer was measured in free field, with the same substantially constant power input to the electric conductor means and the same microphone placement relative to the transducer. The response curves do not of course show the relative intensity of the two acoustic transducers but the relative variances of the intensity level of the two acoustic transducers over the frequency range. As can be seen from FIG. 11, my acoustic transducer gives a more uniform intensity level over the full range of frequencies than does the conical loudspeaker and shows a marked improvement in intensity level at the low frequencies.

Another planar acoustic transducer is shown in FIGS. 12, 13 and 14. The electromagnetic driving means 84 is comprised of a plurality of magnetized members 85 and electric driver means 86. The magnetized members 85 are spaced from each other as in an array and apart from each other to form a plurality of grid-like elongated gaps 87. The supports for magnetized members 85 are not shown in FIGS. 12, 13 and 14. Each magnetized member 85 has a North pole face 88 of planar shape and a South pole face 89 of planar shape. The magnetized members 85 are positioned so that their oppositely polarized faces are spaced adjacent each other along the gaps 87 in either direction of the array to create elongated magnetic fields 90 in the regions like 91 partially inside and partially outside the gaps 87 as shown in FIG. 14. The magnetized members 85 are bridged together and supported by essentially nonmagnetically conductive rib members 95 positioned at the intersections of the grid-like elongated gaps 87. Electric driver means 86 is comprised of independent electric conductor means 92 of substantially flat rectangular spiral coil configurations in regions 91 adjacent the periphery of polarized pole faces 88 and 89 of certain staggered magnetized members 85 in the array, and are attached directly to and supported by either diaphragm 93 or 94. And the electric conductor means 92, positioned on opposite sides of the array of the magnetized members 85, are positioned adjacent the periphery of oppositely staggered magnetized members 85 of the array. The diaphragms 93 and 94 are spaced from and positioned substantially parallel to pole faces and 89 and are positioned parallel to each other. The diaphragms 93 and 94 may be separately supported by essentially non-magnetically conductive and resilient material in the spaces 96 and 97 (not shown), or may be separately or jointly supported by a frame of essentially non-magnetically conductive material adjacent the periphery of the plurality of magnetized members 85 (not shown). In any case, each of the diaphragms 93 and 94 may be a rigid material of curved surfaces as shown in FIG. 14 to position the electric conductor means 92 or they may be membranous material such as varnished cambric (not shown).

The acoustic transducer shown in FIGS. 12, 13 and 14 is believed to operate in essentially the same manner as the acoustic transducer shown in FIGS. 7 and 8 in accordance with the well known electromagnetic principles expressed by the right-hand rule. This embodiment however permits the use of magnetized members 85 of very small size and varied shape and of very large pole face area to thickness ratios and still maintain magnetic fields 90 of high flux density.

Another planar acoustic transducer is shown in FIGS. 15 and 16. The electromagnetic driving means 98 is comprised of a magnetized member 99 and an electric driver means 100. The magnetized member 99 creates a magnetic field 101 and has North pole face 102 of planar shape and a South pole face 103 of planar shape. The supports for magnetized member 99 are not shown in FIGS. 15 or 16. Pole pieces 104 of magnetically conductive material are positioned adjacent the periphery of the magnetized member 99 to form elongated regions 105 of relatively high flux density in magnetic field 101 around the periphery of the magnetized member 99. The pole pieces 104 are supported by magnetized member 99 through spacer members 106 of essentially non-magnetizable material. Electric driver means 100 is comprised of electric conductor means 107 and 108 having a substantially flat spiral coil configuration positioned in said regions 105 of relatively high flux density in said magnetic field 101 and form planes substantially parallel to and spaced from pole faces 102 and 103, and substantially parallel to each other. Electric conductor means 107 and 108 are operably attached to diaphragms 109 and 110 respectively. The diaphragms 109 and 110 are substantially parallel to and spaced from pole faces 102 and 103 respectively and substantially parallel to each other. The diaphragms 109 and 110 may be separately supported by essentially nonmagnetically conductive and resilient material in the spaces 111 and 112 respectively between the magnetized member 99 and the diaphragms 109 and 110 (not shown), or may be separately or jointly supported under tension by frame structure of essentially non-magnetically conductive material around the periphery of the magnetized member 99 (not shown). In either case diaphragms 109 and 110 are made of membranous material such as varnished cambric.

I believe that the operation of this embodiment is due essentially to the well known electromagnetic principles in accordance with the right-hand rule. By this embodiment, the pole pieces 104 intensifies the magnetic fields 101 in regions 105 by conducting the conjugated polarized magnetic flux lines along a much lower reluctance path than air into proximity of the pole faces 102 or 103 and thereby increase the magnetic flux density of the magnetic fields 101 in regions 105 in which the

3,873,784 electric conductor means 107 and 108 are positioned. The forces exerted on the diaphragms 109 and 110 are in turn stronger and result in a more efficient acoustic transducer and in better quality sound reproduction.

An alternative embodiment of the planar acoustic transducer shown in FIG. 15 is shown in FIG. 17. The arrangement of the elements is the same as shown in FIGS. 15 and 16. The shapes of the magnetized member 991; the pole faces 102, and 103,, pole pieces 104, and spacer members 106, have been varied to increase the density of the magnetic field 101, and make it substantially uniform in the regions 105, where the conductor means 107, and 108, are positioned. The pole faces 102, and 103, are curved rather than perfectly planar. In addition, a light substantially rigid patch 113 is overlayed on diaphragm 110, to mechanically shift the phase response of diaphragm 110, so that its frequency response is slightly different from the frequency response of diaphragm 109,. By this arrangement, any spurious frequencies produced by the diaphragms 109, and 110, are radiated at only about one-half their amplitude by virtue of the damping action of the opposite diaphragm.

Another alternative embodiment of the planar acoustic transducer shown in FIG. 15 is shown in FIG. 21. The arrangement and shape of the elements is the same as shown in FIGS. 15 and 16 except that as added elements the electric conductor means 1072 and 1082 are interlaid with and insulated from magnetically conductive material 114 and the diaphragms 1092 and 1102. In operation, I believe that the magnetically conductive material 114 causes the magnetic lines of flux of the magnetic field 1012 formed by the magnetic member 992 to intensify in the regions 1052 where the conductor means 1072 and 1082 are positioned and thereby increases the efficiency of the acoustic transducer and the quality of the sound reproduction of the acoustic transducer.

Still another alternative embodiment of the planar acoustic transducer shown in FIG. 15 is shown in FIG. 18. The arrangement and shape of the elements of the electromagnetic driver means 983 is the same as shown in FIGS. 15 and 16. The frame structure 115 for supporting diaphragms 116 and 117 are shown. The diaphragms 116 and 117 are jointly supported under tension by frame structure 115 of essentially nonmagnetically conductive material adjacent the periphery of the magnetized member 99.,. Each diaphragm 116 or 117 is comprised of membranes 118 and 119 sealed around the edge portions 120 where the diaphragm 116 or 117 attaches to the frame structure 115, and the membranes 118 and 119 are held apart by internal strut members 121 in the area where the electric conductor means 1073 or 1083 is attached to the diaphragm 116 or 117. By this arrangement, the diaphragm 116 or 117 is made sufficiently stiff to respond to the forces exerted by the electric driver means 1003 over substantially the entire surface area of diaphragm 116 or 117 and still be light and complaint enough to be sensitive to very small forces exerted by the electric driver means 1003. In addition, I prefer that the diaphragm 116 or 117 be inflated by virtue of pneumatic pressure to further stiffen and increase the response of the diaphragm 116 or 117 to the forces exerted by the electric driver means 1003. This arrangement permits a marked improvement in intensity level of low frequency sound reproduction.

Another acoustic transducer is shown in FIGS. 19 and 20. The electromagnetic driver means 984 is the same as the electromagnetic driver means 98 shown in FIGS. 15 and 16. The diaphragms 122 and 123 are jointly supported under tension by frame structure 124 of essentially non-magnetically conductive material adjacent the periphery of the magnetized member 99.,. Each diaphragm 122 or 123 is comprised of members 125 and 126 pneumatically sealed around the edge portions 127 where the diaphragm 122 or 123 attaches to the frame structure 124, and are pneumatically sealed at intermediate points 128, 129, 130 and 131 to form sections 132 and 133. The material used for the membranes 125 and 126 is light, compliant material substantially impervious to gases such as air, and capable of forming and sealing with itself readily by the application of heat or adhesives. The sections 132 and 133 are then inflated to form a quilt-like diaphragm 122 or 123, the inflation may be accomplished by assembling the diaphragm 122 or 123 in a room having a pressure different from atmospheric pressure. By this arrangement, the diaphragm 122 or 123 is made sufficiently stiff to respond to forces exerted by the electric driver means 1004 over substantially the entire surface area of diaphragm 122 or 123 and still be light and compliant enough to be sensitive to very small forces exerted by the electric driver means 1004. This in turn permits a marked improvement in intensity level of low frequency sound reproduction. Also by sealing the membranes 125 and 126 together at intermediate, symmetrical or random points 128, 129, 130 and 131 the usual spurious flexures accompanying modulation of a diaphragm are reduced and the quality of the sound reproduction improved.

Still another planar acoustic transducer is shown in FIGS. 22 and 23. The electromagnetic driving means 134 is commprised of a magnetized member 135 and two independent electric driver means 136 and 137. The magnetized member 135 creates a magnetic field 138 and has North pole face 139 of planar shape and South pole face 140 of planar shape. The supports for magnetized member 135 are not shown in FIGS. 22 and 23. The pole pieces 141 of magnetically conductive material are positioned adjacent the periphery of the magnetized member 135 to form elongated regions 142 of relatively high flux density in magnetic field 138 around the periphery of the magnetized member 135. The pole pieces 141 are supported by magnetized member 135 through spacer members 147 of essentially non-magnetizable material. Electric driver means 136 is comprises of electric conductor means 143 having a substantially flat spiral coil configuration positioned in said regions 142 of relatively high flux density in said magnetic field 138. Electric driver means 137 is comprised of electric conductor means 144 having a substantially flat spiral coil configuration positioned adjacent the North pole face 139 of magnetized member 135 and circumscribed by electric conductor means 143. Both electric conductor means 143 and electric conductor means 144 form planes substantially parallel to and spaced from North pole face 139 and are operably attached to diaphragm 145. Diaphragm 145 is made of membranous material such as varnished cambric and is positioned substantially parallel to and spaced from North pole face 139. The diaphragm 145 may be supported by essentially non-magnetically conductive and resilient material in space 146 between the

3,873,784 magnetized member 135 and the diaphragm 145 (not shown), but is preferably supported under tension by frame structure of essentially non-magnetically conductive material around the periphery of the electromagnetic driving means 134 (not shown).

In operation, the electric driver means 136 is believed to respond to the well known electromagnetic principles in accordance with the right-hand rule and the electric driver means 137 is believed to respond to the same as described with respect to FIGS. 1 and 2. The two electric driver means 136 and 137 can be driven, for example, by the same audio signal through electronic filter means so that electric driver means 137 drives diaphragm 145 to reproduce the high frequency sound and electric driver means 136 drives diaphragm 145 to reproduce the low frequency sound.

Still another planar acoustic transducer is shown in FIGS. 24 and 25. The electromagnetic driving means 148 is comprised of a magnetized member 149 and two electric driver means 150 and 151. The magnetized member 149 creates a magnetic field 152 and has a North pole face 153 of planar shape, and has an opening 154 in its center. First pole piece 155 is positioned in the opening 154 to form pairs of spaced apart elongated gaps 158 with magnetized member 149. Second pole pieces 157 are positioned adjacent the periphery of magnetized member 149 to form pairs of spaced apart elongated gaps 158 with magnetized member 149. Electric driver means 150 is comprised of electric conductor means 159 having a substantially flat spiral coil configuration and is positioned in the magnetic field 152 of the magnetized member 149 and substantially parallel to and spaced from said North pole face 153 astride gaps 156. Electric driver means 151 is comprised of electric conductor means 160 having a substantially flat spiral coil configuration and is positioned in the magnetic field 152 of said magnetized member 149 and substantially parallel to and spaced from said North pole face 153 astride gaps 158. Electric conductor means 159 and 160 are operably attached to the diaphragm 161 which is positioned substantially parallel to and spaced from North pole face 153. Diaphragm 161 is made of membranous material such as varnished cambric and has a cap 162 of substantially light, rigid material located at its center and enclosing the area covered by electric conductor means 159. The diaphragm 161 may be supported by essentially nonmagnetically conductive and resilient material in space 163 between the magnetized member 149 and the diaphragm 161 (not shown), but is preferably supported under tension by frame structure of non-magnetically conductive material around the periphery of the electromagnetic driving means 148 (not shown).

I believe that the operation of this embodiment is due essentially to the well-known electromagnetic principles in accordance with the right-hand rule. The two electrically driven means 150 and 151 can be driven for example by the different channels of a stereophonic recording, or as I prefer, by the same audio signal through electronic filter means so that electric driver means 150 drives cap 162 to reproduce the high frequency sound and electric driver means 151 drives diaphragm 161 to reproduce the low frequency sound.

Still another planar acoustic transducer is shown in FIGS. 26 and 27. The electromagnetic driving means 164 is comprised of a magnetized member 165 and an electric driver means 166. The magnetized member

165 creates a magnetic field 167 and has a North pole face 168 of planar shape and a South pole face 169 of planar shape. The supports for magnetized member 165 are not shown in FIGS. 26 and 27. Pole pieces 170 are positioned adjacent to a magnetized member 165 to form pairs of spaced apart elongated gaps 171 with magnetized member 165. Pole pieces 170 are spaced from and supported by the magnetized member 165 through spacer members 172. Partially outside and partially inside said gaps 171 are regions 173 of relatively high magnetic flux density and substantially uniform flux distribution in said magnetic field 167. Electric driver means 166 is comprised of electric conductor means 175 and 176 having substantially flat helically coil configurations positioned in said regions 173 of magnetic field 167 and forms a plane substantially perpendicular to the lines of flux in said regions 173 of magnetic field 167. The electric conductor means 175 and 176 are operably attached to conductor forming means 177 and 178 respectively. Diaphragms 179 and 180 are positioned substantially parallel to and spaced from pole faces 168 and 169 respectively, and position and support conductor forming means 177 and 178 and in turn the electric conductor means 175 and 176 respectively. The diaphragms 179 and 180 may be separately supported by essentially non-magnetically conductive and resilient material in spaces 181 and 182 (not shown), or may be separately or jointly supported under tension by frame structure of essentially nonmagnetically conductive material adjacent the periphery of the magnetized member 165 (not shown). In either case diaphragms 179 and 180 are made of membranous material such as varnished cambric.

In operation, I believe that this embodiment responds to the well known electromagnetic principles in accordance with the right-hand rule and essentially the same as that described with respect to FIGS. 15 and 16. The spacer members 172 have however been made so that they do not fill the entire spaces between the magnetized member 165 and the pole pieces 170 and provide gaps 171. By this arrangement, the electric conductor means 175 and 176 can be positioned partially in the gap where the magnetic flux density is higher and the magnetic flux is more uniformly distributed. In addition, by orienting the electric conductor means 175 and 176 so that said planes formed by them are substantially perpendicular to the lines of flux in said regions 175 of magnetic field 167, the pole pieces 170 can be portions closer to the periphery of the magnetized member 165 and in turn intensify the magnetic flux density in regions 173 of said magnetic field 167. This in turn provides an increase in the efficiency of the acoustic transducer.

An alternative embodiment of the planar acoustic transducer shown in FIG. 26 is shown in FIG. 28. The arrangment of the elements is the same as shown in FIGS. 26 and 27 except for the positioning and shape of the electric conductor means 1751 and 176, and the shape of the conductor forming means 177, and 178,. The electric conductor means 175, and 176, are substantially flat and form planes substantially parallel to the lines of flux in said regions 173, of magnetic field 167,. I prefer in this embodiment that the electric conductor means 175, and 176, be positioned just inside the gaps 171, where the magnetic flux density is believed to be most dense and the magnetic flux distribution is believed to be most near uniform.

3,873,784

Still another alternative embodiment of the planar acoustic transducer shown in FIG. 26 is shown in FIG. 29. The arrangement of the elements is the same as shown in FIGS. 26 and 27 except for the positioning and shape of the electric conductor means 1752 and 1762 and the shape of the conductor forming means 1772 and 1782. The electric conductor means 1752 and 1762 have rectangular cross-sections. I prefer in this embodiment that the electric conductor means 1752 and 1762 be positioned partially inside and partially outside the gaps 1712 so that they are positioned symmetrically within the most dense and most nearly uniformly distributed magnetic flux. In addition, the shape of the conductor forming means 1772 attached to diaphragm 1792 is of a slightly different shape and weight than the conductor forming means 1782. By this arrangement, the frequency response of diaphragm 1792 is mechanically shifted slightly from the frequency response of disphragm 1802 and spurious frequencies produced by diaphragms 1792 and 1802 are not resonated but are dampened.

Another alternative embodiment of the planar acoustic transducer shown in FIG. 26 is shown in FIG. 30. The arrangement of the elements is the same as shown in FIGS. 26 and 27 except for the following changes and additions. Pole pieces 183 and 184 are positioned to adjoin North pole piece 1683 and to adjoin South pole piece 1693 respectively. Said pole pieces 183 and 184 extend slightly beyond the periphery of the magnetized member 1653 and increase the depth of the pairs of spaced apart elongated gaps 1713. By this arrangement, magnetic flux density in the regions 1733 of magnetic field 1673 is intensified in side gaps 1713 and the magnetic flux distribution more uniform insdie gaps 1713. The electric conductor means 1753 and 176:i can be and are in turn positioned further into the gaps 1713 and the efficiency of the acoustic transducer and the quality of the sound reproduction increased.

An alternative embodiment of the planar acoustic transducer shown in FIG. 26 is shown in FIG. 31. The arrangement of the elements is the same as shown in FIGS. 26 and 28 except for the following changes and additions. Pole pieces 1834 and 1844 are positioned to adjoin North pole piece 1684 and to adjoin South pole piece 1694 respectively. Said pole pieces 1834 and 1844 extend slightly beyond the periphery of the magnetized member 1654 and increase the depth of the pairs of spaced apart elongated gaps 1714. The results of this arrangment are substantially the same as described above in connection with FIG. 30. Further, the shape of the conductor forming means 1774 and 1784 are different from the shape of the conductor forming means 1772 and 1782, and in addition are slightly different in shape from each other. In this way, a substantial surface area of the conductor forming means 1774 and 1784, and in contact with the diaphragms 1794 and 1804 and aid in driving them over substantial portions of their areas, and the frequency response of diaphragm 1794 is mechanically shifted slightly from the frequency response of diaphragm 1804. This arrangement in turn increases the frequency response of the transducer at low frequencies and spurious frequencies produced by diaphragms 1794 and 1804 are not resonated but are dampened.

Still another alternative embodiment of the planar acoustic transducer shown in FIG. 26 is shown in FIG. 32. The arrangement of the elements is the same as shown in FIGS. 26 and 29 except for the following changes and additions. Pole pieces 183-, and 184r, are positioned to adjoin North pole piece 168.-, and to adjoin South pole piece 1695 respectively. Said pole pieces 1835and 1845 extend slightly beyond the periphery of the magnetized member 1655 and increase the depth of the pairs of spaced apart elongated gaps 1715. The results of this arrangement are substantially the same as described above in connection with FIG. 30.

To illustrate the advantages of the hereinbefore described embodiments of my acoustic transducer I have compared the performance of the embodiments shown in FIGS. 15 and 16 and 26 and 30 with a high quality 8 inch conical loudspeaker. I compared these transducers over the range of acoustic frequencies, i.e., from about 30 cycles per second to about 10,000 cycles per second. The results are shown in FIG. 33. Curve A is my acoustic transducer as described above and shown in FIGS. 15 and 16 with approximately 120 square inches diaphragms 109 and 110 made of varnished cambric, about 4.5 in. X2 in. spiral electric conductor means 107 and 108 having 18 turns No. 32 gauge wire each, and diaphragms 109 and 110 supported by frame structure positioned around the periphery of the magnetized member 99. Curve B is my acoustic transducer as above described and shown in FIGS. 26 and 30 with approximately 120 square inches diaphragms 179:1 and 1803 made of varnished cambric, about 4.5 in. X2 in. helical electric conductor means 1753 and 1763 having 18 turns No. 32 gauge wire each, and diaphragms 179:1 and 1803 supported by frame structure positioned around the periphery of the magnetized member 1653. Curve C is my acoustic transducer as above described and shown in FIGS. 26 and 30 the same as Curve B with the addition of a rigid patch 113 (shown in FIG. 17) overlayed on one of the diaphragms to dampen resonance of diaphragms 1793 and 180:i. Curve D is a good quality 8 inch loudspeaker. The performance of each transducer was measured in free field, with the same substantially constanct power input to the electric conductor means and the same microphone placement relative to the transducer. The above described response curves shown in FIG. 33 do not of course show the relative intensity of the acoustic transducer, but show the relative variances of the intensity level of the transducer at different frequencies. As can be seen from FIG. 33, my acoustic transducer (save for Curve B) gives a more uniform intensity level over the full range of frequencies than does the conical loudspeaker and shows a marked improvement in intensity level at the low frequencies. It should be noted with respect to Curve A that the sharp dip at 1,200 cycles per second is due to a fabrication factor which can be easily corrected and is not indicative of performance of my acoustic transducer. In addition, by comparing Curves B and C it can readily be seen that the slight mechanical shift in the frequency response of one of the diaphragms by adding the patch 113 substantially improves the performance of my acoustic transducer.

Still another planar acoustic transducer is shown in FIGS. 34 and 35. The electromagnetic driving means 185 is comprised of a magnetized member 186 and an electric driver means 187. The magnetized member 186 creates a magnetic field 188 and has a North pole face 189 of planar shape and a South pole face 190 of planar shape. The supports for magnetized member 186 are not shown in FIGS. 34 and 35. First pole pieces

3,873,784

191 are positioned to adjoin North pole face 189 and South pole face 190. Second pole pieces 192 of substantially U-shape are positioned adjacent magnetized member 186 to form pairs of spaced apart elongated gaps 193 with first pole pieces 191. Second pole pieces 192 are spaced from and supported by the magnetized member 186 through spacer member 194. Said gaps 193 contain regions 195 in said magnetic field 188 of relatively high magnetic flux density and substantially uniform magnetic flux distribution, i.e., approaching linearity. Electric conductor means 196 and 197 having substantially flat helically coil configurations are positioned in said gaps 193 and form planes substantially perpendicular to the lines of magnetic flux in said gaps 193. The electric conductor means 196 and 197 are supported by conductor forming means 198 and 199 of substantially U-shape. Diaphragms 200 and 201 are positioned substantially parallel to and spaced from pole faces 189 and 190. The electric conductor means 196 and 197, conductor forming means 198 and 199, and magnetized member 186 are positioned relative to each other by resilient, essentially non-magnetically and thermally conductive material 202 and 203, such as highly compliant rubber or foam resin, between the first pole pieces 191 and the conductor forming means 198 and 199.

The pole faces 189 and 190 of said magnetized member 186 shown in FIG. 34 have peripheries in the configuration of circles. The peripheries of the pole faces 189' and 190' of said magnetized member 186’ may however be in the configuration of elipses as shown in FIG. 36. I prefer that the pole faces 189 and 190 be in the shape of elipses or rectangles rather than circles as shown in FIG. 34 because the larger the perimeter for a given area, the greater the efficiency of the transducer.

I believe that the operation of this embodiment is due essentially to the well known electromagnetic principles in accordance with the right-hand rule. This embodiment illustrates that the electromagnetic driving means 185 can be an intermediate assembly. Such electromagnetic driving means 185 can be disposed geometrically or randomly over a mounting surface and covered with a single diaphragm or sections of diaphragrrie to form an acoustic transducer.

Still another planar acoustic transducer particularly adapted for use in automobiles is shown in FIG. 37. The electromagnetic driving means 204 is comprised of a magnetized member 205 and an electric driver means 206. The magnetized member 205 creates a magnetic field 207 and has a North pole face 208 of planar shape and a South pole face 209 of planar shape. The supports for magnetized member 205 are not shown in FIG. 37. First pole piece 210 is positioned to adjoin North pole face 208. Second pole piece 211 of substantially U-shape adjoins South pole face 209 and forms pairs of spaced apart elongated gaps 212 with said first pole piece 210. Said gaps 212 contain regions of relatively high flux density in the magnetic field 207 of magnetized member 205. Electric driver means 206 is comprised of electric conductor means 213 and conductor forming means 214. Electric conductor means 213 having a substantially flat helically coil configuration is positioned in said gaps 212, and forms a plane substantially perpendicular to flux lines of said magnetic field 207 in said gaps 212. Electric conductor means 213 are supported by conductor forming means

214. Conductor forming means 214 of substantially Ushape is operably attached to diaphragm 215 and positioned substantially parallel to and spaced from said North pole face 208. The electric conductor means 213, conductor forming means 214 and magnetized member 205 are positioned relative to each other by resilient, essentially non-magnetically and thermally conductive material 216 between the pole pieces 210 and 211 and conductor forming means 214.

I believe the operation of this embodiment is due essentially to the well known electromagnetic principles in accordance with the right-hand rule. For installation in an automobile 1 contemplate that the electromagnetic driving means 204 be made as an intermediate assembly. The electromagnetic driving means 204 will be positioned in the automobile by rigidly fastening second pole piece 211 to the roof 217 of the automobile and then the headliner 218 of the automobile be positioned and fastened to conductor forming means 214 to form the diaphragm 215.

Still another planar acoustic transducer is shown in FIG. 38. The electromagnetic driving means 219 is comprised of a magnetized member 220 and an electric driver means 221. The magnetized member 220 creates magnetic field 222 and has North pole face 223 of planar shape and South pole face 224 of planar shape. The supports for magnetized member 220 are not shown in FIG. 38. First pole pieces 225 are positioned to adjoin North pole face 223 and South pole face 224. Second pole pieces 226 are positioned adjacent to and spaced from said first pole pieces 225 and to form pairs of spaced apart elongated gaps 227. Gaps 227 contain regions of relatively high flux density in magnetic field 222 of substantially uniform flux distribution formed by magnetized member 220. Said second pole pieces 226 are supported by magnetized member 220 through spacer members 228. Electric conductor means 229 is positioned in the gaps 227 supported by a conductor forming means 230. Conductor forming means 230 is in turn supported by operably attached to two diaphragms 231 and 231’ which are positioned substantially parallel to and spaced from North pole face 223 and South pole face 224. The supports for diaphragms 231 and 231* are not shown in FIG. 38.

In addition, a light substantially rigid patch 174 is overlayed on diaphragm 231* to mechanically shift the phase response of diaphragm 2311 so that its frequency response is slightly different from the frequency response of diaphragm 231. By this arrangement, any spurious frequencies produced by the diaphragms 231 and 2311 are radiated at only about one-half their amplitude by virtue of the dampening action of the opposite diaphragm.

In FIGS. 39 and 40 are shown the electric driver means 221 for the planar acoustic transducer shown in FIG. 38. Sections 232 of insulated backing of nonmagnetically conductive material form the conductor forming means 230. Sections 233 of conductive pathway patterns are fixed to sections 232 of insulated backing. Sections 233 of conductive pathway patterns are of a flat spiral coil shape. Sections 233 of conductive pathway patterns are connected together by conductive pathways 234 fixed to the opposite sides of section 232 of insulated backing.

In manufacture, the electric driver means can be formed by printed circuit, printed wiring, or pressed wiring method. The sections 233 of conductive path3,873,784 way patterns are formed in this way on the sections 232 of the insulated backing, and the connectors 234 made at the same time. The electric driver means 221 as shown in FIG. 39 can then be formed into the closed electric driver means as shown in FIG. 40. The connectors 234 are positioned on the closed side of the sections 232 of insulated backing so that the connectors 234 are subjected to compression as the electric driver means 221 is formed.

The acoustic transducer as shown in FIG. 38 can be made by a method comprising the following steps: The first pole pieces 225 can be adjoined to the magnetized member 220. A spiral coil conductor means 229 can be formed of sections 233 of conductive pathway patterns on sections 232 insulating backing i.e., the conductor forming means 230. Said electric conductor means 229 and the conductor forming means 230 can then be formed around the periphery of and spaced from said magnetized member 220. Spacer members 228 can then be positioned through openings 235 in said electric conductor means 229 to adjoin said magnetized member 220. Second pole pieces 226 can be positioned to adjoin spacer members 228 and form spaced apart pairs of elongated gaps 227 with said first pole pieces 225. Two diaphragms 231 can be operably attached to conductor forming means 230 by suitable means.

A modular array of one embodiment of my acoustic transducer is shown in FIG. 41. The arrangement and shape of the elements of the transducer are the same as above described and shown in FIGS. 15 and 16. The diaphragms 109 and 110 are jointly fastened and supported under tension at edge portions 247 by frame structure 245 of essentially non-magnetically conductive material around the periphery of the magnetized member 99. The magnetized member 99, pole pieces 104 and spacer members 106 are supported as an assembly by rib members 246 which in turn fasten rigidly to frame structure 245. The entire modular array can be formed by any suitable decorative means 245 and covered over with a pervious material such as cloth (not shown).

A modular array of one embodiment of my acoustic transducer especially adapted for mounting on a wall is shown in FIG. 42. The arrangement and shape of the elements of the transducer are the same as above described and shown in FIGS. 15 and 16. The diaphragms 109 and 110 are jointly fastened under tension at edge portions 138 by frame structure 239 of essentially nonmagnetically conductive material around the periphery of the magnetized member 99. The magnetized member 99, pole pieces 104 and spacer members 106 are supported as our assembly by rib members 240 which in turn fasten rigidly to frame structure 239. Two such transducer assemblies 241 are mounted in a stacked array on frame structure 242 so that the diaphragm 110 is substantially the same distance from diaphragm 1091 of the adjacent transducer assembly 2411 as it is from diaphragm 109 of transducer assembly 241. The electric conductor means 107 and 108 of both transducer assemblies are driven by the same audio signal. By the arrangement, the ambience behind the transducer assembly 241 is moved so that the diaphragms 109 and 110 do not see a dead air space but rather a moving diaphragm which serves to reduce the effect of the high resistance to compressibility of an enclosed air volume.

To illustrate the advantages of the above described assembly of my acoustic transducer I have compared the performance of an 8 modular array of the embodiment as shown in FIGS. 15 and 16, and FIGS. 26 and 30 having the diaphragms on one side of the array overlaycd with a rigid patch 113 (see FIG. 17) with other full range loudspeaker systems. I compare these transducers over the range of acoustic frequencies, i.e., from about 30 cycles per second to about 10,000 cycles per second. The results are shown in FIG. 43. Curve A is an 8 modular array of my acoustic transducer as described above and shown in FIGS. 15 and 16 with approximately 120 square inches diaphragms 109 and 110 made of varnished cambric about 4.5 in. X 2 in. spiral electric conductor means 107 and 108 having 18 turns No. 32 gauge wire each, and diaphragms 109 and 110 supported by frame structure positioned around the periphery of each magnetized member 99. Curve B is an 8 modular array of my acoustic transducer as above described and shown in FIGS. 26 and 30 with approximately 120 square inches diaphragms 1793 and 180;j made of varnished cambric, about 4.5 in. X 2 in. helical electric conductor means 1753 and 1763 having 18 turns No. 32 gauge wire each and diaphragms 1793 and 1803 supported by frame structure and positioned around the periphery of the magnetized member 1653. Curve C is a good quality 8 inch conical loudspeaker model. Curve D is a good quality bass reflex system. The performance of each transducer was measured in free-field, with the same substantially constant power input to the electric conductor means in the same microphone placement relative to the transducer. The above described response curves shown in FIG. 43 do not show the relative intensity level of the transducer, but show the relative variances of the intensity level of the transducer at different frequencies. This can be seen from FIG. 43 my acoustic transducer gives a more uniform intensity level over the full range of frequencies than does the other transducers tested and shows a marked improvement in intensity level at the low frequencies.

While I have shown and described certain presently preferred embodiments of my invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied within the scope of the following claims.

Every citation, both ways

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Document	Office	Kind	Date
34617173	United States of America	A	1973-03-29
887557	–	–	–
US19730346171	–	–	–

Acoustic transducer

Abstract

Term

PATENTED MAR 2 5 1975 3,873 784

SHEET 01 OF 15

SHEET 02 OF 15

PATENTEDMAR25I975

SHEET OU GF 15

SHEET C 5 OF 1 5

PATENTED MR 2 5,975

SHEET CG OF 15

PAI EHTED HAR2 51975

SHEET 0 7 OF 15

SHEET 08 OF 15

PATENTED KAR251975

SHEET 10 OF 15

PATENTEDHA825IST5

PATENTED MR 2 51975

SHEET 12 OF 15

PATENTED WAR 2 51975

SHEET 13 OF 15

SHEET 1 U OF 15

PATENTEDMAR25I375

SHEET 15 OF 15

ACOUSTIC TRANSDUCER

XXVII-XXVII;

Priority claims3

Numbers

Titles

Classification