Electromagnetic transducer

[57] ABSTRACT

An electromagnetic transducer utilizing one or more vibratable diaphragms, each carrying one or more conductors which may be stacked upon each other on the diaphragm, and a flexible sheet magnet confronting the diaphragm and spaced therefrom and being magnetized in a direction through its thinnest dimension in elongate zones, following the configuration of the conductors on the diaphragm, the sheet magnet lying against a panel of ferromagnetic material; another diaphragm optionally located at the opposite side of the magnet, the diaphragm being stretched in many embodiments and numerous vibratable areas with different resonant frequencies.

Claims, 34 Drawing Figures

<img file="US3674946A_D0001.tif" />

PATENTED JUL 4 1972

3,674,946

SHEET 1 OF 7

<img file="US3674946A_D0002.tif" />

<img file="US3674946A_D0003.tif" />

36 31 36 31b

<img file="US3674946A_D0004.tif" />

<img file="US3674946A_D0005.tif" />

s/rT-aeAWs

PATENTED JUL 4 1972

3,674,946

SHEET 2 OF 7

<img file="US3674946A_D0006.tif" />

<img file="US3674946A_D0007.tif" />

PATENTED JUL 41972

SHEET 3 OF 7

3,674,946

<img file="US3674946A_D0008.tif" />

Tw9

36-5

31.5

30.5 // M

34.5

Twin

N

31.5

<img file="US3674946A_D0009.tif" />

<img file="US3674946A_D0010.tif" />

50 100 200 500 1000 2000 5M

FREQUENCY

T1013

IOM 20M

INVENTOR.

c/4MES Al. W/AJEV

<img file="US3674946A_D0011.tif" />

PATENTED JUL 41972

3,674,946

SHEET U OF 7

<img file="US3674946A_D0012.tif" />

<img file="US3674946A_D0013.tif" />

JAMES M. H/zaJER' BY ,

<img file="US3674946A_D0014.tif" />

ΛΓΤΌ&amp;Ι/ΕΡίΖ

PATENTEOJUL 4 1572

3,674,946

SHEET 5 OF 7

<img file="US3674946A_D0015.tif" />

PATENtEDM 41972

3,674,946

SHEET 6 OF 7

<img file="US3674946A_D0016.tif" />

<img file="US3674946A_D0017.tif" />

<img file="US3674946A_D0018.tif" />

Tw 29

INVENTOR.

C/4M4S M. W/ME'S

<img file="US3674946A_D0019.tif" />

4T TORAZEE'S

PATENTED JUL 41972

3,674,946

SHEET 7 OF 7 £K UJ

<img file="US3674946A_D0020.tif" />

INVENTOR.

CRIMES At W/AJE^

<img file="US3674946A_D0021.tif" />

^TTOEAJEp'S

3,674,946

ELECTROMAGNETIC TRANSDUCER

Electromagnetic transducers of the type using a vibrating diaphragm and a relatively flat and broad magnet have been known before, but, in view of the type of materials used in such transducers, such prior transducers were costly to 5 produce, fragile to use and handle, and difficult to work with, particularly in the fabrication of such transducers. The magnets used in such transducers were made of a rigid, cast or sintered magnetic material, oftentimes a barium ferrite, which is necessarily relatively thick, on the order of three-eighths to 10 one-half inch in many instances, and in large broad sheets more than a few inches in area, the ferrite material is considerably thicker in order to be self-supporting and capable of withstanding breakage. The extreme thickness of the magnetic panels has the effect to make a severe limitation as to the 15 minimum width of the magnetized bands or zones, and the spacing between these magnetic bands. Because the material is thick, the width of these bands must be on the same general order as the thickness of the material.

In addition, the previously known electromagnetic transdu- 20 cers of this type had severe limitations because of the resonant problems encountered with the vibrating diaphragms, and these electromagnetic transducers have had poor polar distribution of generated sound. The vibrating diaphragm type of transducer produces an essentially directional sound pattern. 25 Also, problems have been encountered with the previously known transducers of this type in regard to the level of sound output producable.

These and other problems have been encountered and solved with the present invention. 30

BRIEF SUMMARY OF INVENTION

This invention has numerous important aspects. One of the important aspects is the use of the perforate flexible sheet magnet which may be of oriented or non-oriented synthetically fabricated material. The sheet material in the diaphragm is actually stretched beyond its original dimensions, not just pulled taut as is known previously. Also, the transducer uses stacked conductors on the diaphragm and stacked diaphragms that work together and produce increased energy output, with or without multiple stacked sheet magnets.

The present invention facilitates production of sound output over a broad range of audio frequencies, from the lowest audible frequencies, 16 to 20 cps. to at least 15,000 to 20,000 cps. Across this audible frequency range, outputs can be maintained at a relatively constant level.

These and other advantages will appear more fully in the appended specification in connection with the drawings which are described as follows.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings, certain of the parts, and particularly the diaphragms, are shown disproportionately thick in order to be visible in the drawing. Approximate dimensional characteristics are set forth in the specification in order to make the invention understandable.

HG. 9 is an enlarged detail section view of still another embodiment of the invention.

HG. 10 is an enlarged detail section view of still another embodiment of the invention.

HG. 11 is an enlarged detail section view of still another embodiment of the invention.

HG. 12 is an elevation view of another embodiment of a transducer incorporating the present invention.

HG. 13 is a frequency response curve relating to the transducer of HG. 12.

HG. 14 is an enlarged detail section view taken approximately at 14—14 of HG. 12.

HG. 15 is an enlarged detail section view taken at 15—15 in FIG. 12.

HG. 16 is an enlarged detail section view illustrating still another embodiment of the invention.

FIG. 17 is an elevation view of another form of transducer embodying the present invention.

HG. 18 is an enlarged detail section view taken at 18-18 in FIG. 17.

HG. 19 is an enlarged detail section view illustrating still another embodiment of the invention.

HG. 20 is an elevation view of a transducer constituting still another embodiment of the invention.

HG. 21 is an enlarged detail section view taken at 21—21 in FIG. 20.

FIG. 22 is an enlarged detail section view of still another embodiment of the invention.

FIG. 23 is a plan view of still another embodiment of the invention.

FIG. 1 is a perspective view of an electromagnetic transducer incorporating the present invention and specifically comprising a sound generating speaker.

FIG. 2 is an enlarged detail transverse section view taken at 2—2 in FIG. 1.

FIG. 3 is an enlarged detail section view taken approximately at 3—3 in FIG. 2.

FIG. 4 is an enlarged detail plan view of a portion of the speaker shown in HG. 1 and with the several laminae broken away for clarity of detail.

FIG. 5 is an enlarged detail section view patterned after FIG. 3, but showing a modified form of the invention.

FIG. 6 is another enlarged detail section view of still another modified form of the invention.

FIG. 7 is an enlarged detail plan view of the form of the transducer illustrated in FIG. 6.

FIG. 8 is an enlarged detail section view of still another embodiment of the invention.

FIG. 24 is an enlarged detail section view taken approximately at 24—24 in FIG. 23.

FIG. 25 is an enlarged detail section view of a transducer 35 embodying still another form of the invention.

HG. 26 is an enlarged detail section view of still another embodiment of the invention.

HG. 27 is an enlarged detail section view taken approximately at 27—27 in FIG. 26.

FIG. 28 is a diagrammatic view showing the manner of magnetizing in the magnetic fields of the flexible sheet magnet.

HG. 29 is an enlarged diagrammatic view showing another mode of magnetizing and the magnetic fields of the sheet maenet. ⁶⁴⁵ FIG. 30 is an elevation view of another embodiment of a transducer incorporating the present invention.

FIG. 31 is a graph diagrammatically indicating the tension applied in a direction transversely across the width of the diaphragm in the transducer of FIG. 30 and at the various lo^DU cations along the length of the transducer.

FIG. 32 is an elevation view of still another form of transducer embodying the present invention.

FIG. 33 is an elevation view of another embodiment of ₅₅ transducer incorporating the present invention.

FIG. 34 is an elevation view of an additional embodiment of a transducer incorporating the present invention.

DETAILED DESCRIPTION OF THE INVENTION 60 In the drawings the spacings and sizes of the elements are somewhat disproportionate as compared to actual dimensions, so as to make the elements clearly visible and understandable in the drawings. The spacings, sizes and thicknesses, especially of the diaphragms and conductors must be considered to be 65 relatively diagrammatic.

One form of the invention is shown in HGS. 1-4. The transducer is indicated in general by numeral 30. The transducer includes a diaphragm 31 which may be constructed of any of a number of film type materials and may have a thickness rang70 ing from a few microns to approximately 1 % mills in thickness. The diaphragm 31 may be constructed of polyester film, known by its common name. Mylar, and this particular film is preferably stretched when used as the diaphragm. The polyester film may be stretched as much as 5 percent in excess 75 of its original dimensions to stay within the elastic limits, but it

3,674,946 has been found successful to stretch the film approximately 1 percent in excess of its original dimensions so as to have a somewhat lower resonant frequency and also this minimal stretch will prevent any material give or creep in the material over a period of time so that the tension on the material will remain approximately constant for long periods of time.

The diaphragm 31 is stretched in both directions of its length and width, but it should be understood that the diaphragm may be stretched in only one direction, and merely pulled taut in the other direction to eliminate wrinkles. Because the transducer 30 is nearly as wide as it is long, and reasonably small in size, the diaphragm 30 is substantially uniformly tensioned and stretched throughout its entire area. However, the diaphragm may be non-uniformly tensioned and stretched if the transducer has an appropriate shape such as the long and narrow shape hereinafter more fully described in connection with FIG. 30. In such a shape, the tension is applied in a direction across the width of the transducer, and the _____________________________„_e „„_WUIU1 tension may be uniformly varied from one end of the trans- 20 °? P³*¹®^{1 35 of sheet} magnet 34 to obtain the proper reladucer to the other. As a result of the non-uniform tensioning * ¹ — of the diaphragm, the diaphragm will not have any single set of resonant frequencies, but various portions of the diaphragm will resonate at various frequencies so as to make possible the utilization of these resonant frequencies in improving the out- 25 put of the transducer at the extremely low audible frequencies and to make the transducer output more nearly uniform throughout the audio range.

Alternately, the diaphragm 31 may be constructed of other synthetic material known as saran, or may be Constructed of ³⁰plyofilm which is basically a rubber type material; or the diaphragm may be constructed of paper or catgut, or polyethylene. In addition, it may be desirable in certain instances to construct the diaphragm 31 of sheet styrofoam which may be formed with corrugations around the periphery at which point the styrofoam diaphragm will flex. The foregoing is a list of but a few examples of materials from which the diaphragm can be formed, it being important that the diaphragm be relatively light in mass so that it can move quickly at relatively high audio frequencies.

The transducer 30 has a peripheral frame serving as a spacer strip 32 to which the periphery 31a of the diaphragm is adhesively secured, but could, of course, be mechanically clamped. The frame or spacer strip 32 is sufficiently rigid as to withstand the permanent tension on the diaphragm 31.

The frame 32 defines an enlarged central opening 32a confronting the vibratable area 316 of the diaphragm.

An acoustically transparent backing or perforate magnetic panel means 33 is secured to the strip 32 in closely spaced relation to the diaphragm 31, and includes a perforate,oriented or non-oriented, non-sintered flexible plastic sheet magnet 34 lying flush against a perforate, stiff panel 35 of ferromagnetic material such as light gauge galvanized sheet iron. The stiff panel 35, which may serve as the frame in many instances, covers the entire opening 32α of the frame and is secured by adhesive to the frame strips 32 which may be constructed of styrene or other rigid material. As well illustrated in FIG. 2, the panel 35 is panned or dished slightly so that the upper surface thereof is slightly concave. Although the thickness of the panel 35 has not been found to be extremely critical, it has been found that the panel may be of approximately 18 to 24 gauge galvanized sheet metal, or approximately 0.050 inches thickness. The panel 35 is creased slightly in a ₆₅direction diagonally between the comers so as to maintain the panned or dished shape. The dished shape has also been successfully produced by anchoring the edges of the panel 35 securely, and depressing the center of the panel beyond the elastic limit so that the dished shape deformation is per- 70 manent. It will be noted that, because of the type of material used in the pole piece panel 35, the panel 35 cannot maintain its shape with absolute precision, and there may be some minor undulations in the character of the upper surface thereof without adversely affecting the transducer 30.

The flexible plastic sheet magnet 34 has a thickness on the same order as the thickness of the panel 35 and it has been found that thickness of0.050 to 0.060 is satisfactory. The flexible sheet magnet 34 is formed of any suitable material, but it has been found that a plastic rubber bonded barium ferrite magnetic material known by its trademark Plastiform sold by Minnesota Mining &amp; Manufacturing Company of St. Paul, Minn., has proven to be satisfactory. This flexible plastic sheet magnet is extremely ductile and may be easily cut, slit, punched, shaped, drilled, milled and otherwise fabricated into the desired shapes with a minimum of difficulty and machinery. The plastic flexible sheet magnet is sufficiently thin as to be readily pliable and will, by virtue of its own magnetism, when magnetized, pull itself flush against the face of the metal pole piece panel 35, without regard to any minor undulations in the surface of the panel and will conform to the dished or panned shape of the panel caused by the diagonal crimping ^corner fo corner. There need be no milling or smoothing tionship therebetween. As a result of the magnetic attraction between the sheet magnet 34 and the metal panel 35, the sheet magnet will assume the same dished shape as the panel, and there is essentially no gap whatever between the adjoining faces of the sheet magnet 34 and the panel 35 so that the magnetic characteristics of the magnet and its magnetic fields as relates to and is caused by the sheet magnet 34 is optimized and is relatively constant over the entire surface area of the sheet magnet 34.

Although the sheet magnet 34 is illustrated in a unitary construction, it should be understood that the sheet magnet could be made up of numerous strips of the flexible rubber bonded barium ferrite magnetic material or an equivalent magnetic material.

It will be recognized that the perforations 34α in the sheet magnet are aligned with the perforations 35α in the metal panel 35 so as to permit adequate movement of air through these perforations as the diaphragm 31 vibrates.

Although the drawings illustrate substantially uniform spacing between uniformly sized perforations or apertures in the sheet magnet and metal panel, the apertures may be spaced farther apart or may be smaller in size near the edge of the diaphragm where the excursions of the diaphragm are rather minimal. Likewise, it may be desirable in certain instances to plug or omit certain of the perforations or apertures in the sheet magnet and metal panel near the center of the speaker where the excursions of the diaphragm are at a maximum so as to dampen the diaphragm movement and sound production at 5θ resonant frequencies of the diaphragm which might actually otherwise cause slapping of the diaphragm against the sheet magnet 34.

The dished shape of the sheet magnet 34 and panel 35 is primarily to accommodate the maximum excursions of the 55 diaphragm 31, which generally occur during production of low frequency audio sounds. In the transducer 30, the maximum spacing between the diaphragm 31 and the center of the sheet magnet 34, as illustrated in FIG. 2, is approximately 0.040 inches; but at the outer edge of the sheet magnet 34, the ₆₀ spacing between the magnet and the diaphragm need only be approximately 0.009 inches. In many instances, the outer edge of the diaphragm may lie against the sheet magnet.

The diaphragm 31 has a number of conductors 36 adhesively secured thereto. The conductors 36 are shown in FIGS. 1-4 to be only one lamination thick, but could be stacked in insulated relation onto the diaphragm, somewhat in the manner illustrated in FIGS. 6 or 8. The conductors are arranged on the vibratable area 316 of the diaphragm in closely spaced and juxtaposed parallel runs such that the current in adjacent runs of the conductor moves in opposite directions. The conductors 36 are applied to the diaphragm after the diaphragm has been tensioned and stretched, and are constructed of a metallic foil with an adhesive backing applied directly to the diaphragm. The ends of the foil conductor 36 are connected to leads 36 for the purpose of connecting the transducer into

3,674,946 w the output of an audio amplifier so as to supply a signal to the transducer. If certain stretchable conductors are used they may be attached to the diaphragm before tensioning; otherwise the diaphragm may be tensioned in a direction transverse to the runs of the conductors. Other types of conductors have been found to be successful and may include wire printed conductors and conductor formed printed circuit techniques and conductors formed by vapor deposits and similar techniques.

The closeness of spacing between the runs of the conductor 36 is related to the flexibility of the sheet magnet 34 because the sheet magnet may be relatively thin as illustrated because of its flexibility, and because of the thinness, the magnetic zones or bands of the sheet magnet 34 may be relatively narrow and close together. As illustrated in HG. 3, the sheet magnet 34 is magnetized through its thinnest dimension in elongate zones arranged in the sheet magnet 34 in the same configuration as the configuration and spacing of the runs of the conductor 36 on diaphragm 31. It will be noted that the magnetized zones or bands in the sheet magnet 34 define pole faces at the top surface of the sheet magnet, and these pole faces alternate between north and south in the areas between adjacent runs of the conductor, thereby creating the magnetic fields and flux lines which intersect the conductors 36 and coact with the fields produced adjacent the conductors when current flows therein in order to produce the movement or vibration of the diaphragm.

It has been found that with a sheet magnet 34 of approximately 0.060 inches thickness, the spacing between the ad- .,. _{ulc lulm UU1}j cent magnetized zones or bands in the sheet magnet may be 30 36.3 are stacked approximately five-sixteenths of an inch, center to center, and a conductor strip, approximately three-sixteenths of an inch wide and spaced apart by one-eighth of an inch operates satisfactorily. It has also been found that the perforations 34α large size as to provide 20 to 25 percent open area in order to produce low frequency audio sounds by vibration of the diaphragm. The perforations 34α and 35α may be approximately one-sixteenth of an inch in diameter on one-eighth inch spacings in order to achieve the desired proportion of 40 open area. Although this amount of open area is not needed adjacent the edges of the sheet magnet 34 because the excursions of the diaphragm are considerably less than at the center, manufacturing techniques may make the uniform spacing more practical. Adjacent the edge of the sheet magnet ⁴⁵34, only 5 percent open area may be necessary. There need be no correlation between the size of and spacing between the perforations 34α and the spacing of the magnetic zones or bands in sheet magnet 34.

The vibratable area 316 of the diaphragm may be approximately 8 inches wide. Spacing between the sheet magnet and the diaphragm may be on the order of 0.040 inches at the center of the sheet magnet and 0.009 inches at the edge of the vibratabie area.

It will be understood that the magnetic panel 35, against which the sheet magnet 34 lies, provides a low reluctance path for the magnetic field at the lower side of the sheet magnet 34 and the effect is to draw the magnetic field and flux lines adlines then pass through the area of the runs of conductor 36 so that as the electrical current passes through the runs of the conductor 36, the field caused by the current intersects and _uv aunesives mr^iv cooperates with the magnetic fields of the sheet magnet 34 as 65 magnet 34 λ to produce motion in the diaphragm 31, and as thTcurrem ™ °^{f Λβ} and electrical field produced thereby changes direction rapidly, the vibration of the diaphragm is induced.

The low reluctance path has essentially no gaps whatsoever and 35α should be close enough together and of sufficient 35

Although the transducer 30 is illustrated to be rectangular or nearly square in configuration, it should be realized that the ansducer could have other common shapes such as that of a circle, ellipse or triangle, or other irregular shapes such as a kidney shape or the shape of a leaf of a tree

In HG 5, the transducer 30.1 is essentially the same as that d^nbedm connection with HGS. I-*, except that the magnetic panel 35.1 is essentially flat rather than dished. CorrespondmgJy.the flexible sheet magnet 34.1 is likewise essentially flat, and the spacing between the sheet magnet and the “apnragm 31 1 is essentially constant across the length and ^breadffi of file transducer 30.1. In this form of the transducer, tile flexible sheet magnet 34.1 also lies flush against the panel ₁₅ 35.1 and maintains a constant relationship with the panel without any need for machining or flattening of either of the adjoining faces of the sheet magnet or panel. The spacer 32 1 is likewise somewhat larger in this form of the invention as compared to that previously described.

,22^^6and,⁷.’^{Λβ transducer 302} *s essentially the same as tiiat illustrated m HGS. 1-4, excepting that the diaphragm 31.2 has conductors 36.2 on both the upper and lower surfaces thereof. This arrangement of interconnected conductors is one way of stacking conductors on the diaphragm so that in25 creased signal current can be carried to produce additional reaction between the electric fields of the current in the conductors and tile magnetic fields so as to increase the excursion and output of sound from the diaphragm 31 2

Tn the form illustrated in HG. 8, a plurality of conductors ^uP°^{n eacb} other and insulated from each other on both the top and bottom surfaces of the diaphragm 31.3. In dotted lines, additional stacks of conductors are illustrated. It will be noted that all of the conductors in any one stack are clustered together so that the interaction between the electric fields and the magnetic fields of the sheet magnet 34.3 is increased so as to increase the magnitude of output caused by vibration of the diaphragm which actually has larger ^e”^{ns due to} “creased interaction between the fields

Tne form of transducer 30.4 in HG. 9 is essentially the same as illustrated in HGS. 1-4 except that the pole piece panel 35.4 is flat rather than dished and the sheet magnet 34.4 is likewise flat. In this respect, this form of the invention is quite similar to that fllustrated in HG. 5. Also, in FIG. 9, an additional sheet magnet 34.4' is applied to the rear side of the panel 35.4, and another diaphragm 31.4' is similarly positioned m confronting relation with the sheet magnet 34.4 and spaced therefrom by the spacer 32.4'. Similarly, the diaphragm 31.4' carries conductors 36.4' which carry signal 50 ^CUI5^e^ts· ^the electric fields of which interact with the magnetic fields of the sheet magnet 34.4' to produce vibration of the diaphragm 31.4', and because the same signals are supplied to the conductors 36.4 and 36.4', the diaphragms move in synchronism with each other, and in the same direction 55 causing air to pass through the perforations in the panel 35 4 and through the sheet magnets as the sound is produced. It will be understood that additional stacked conductors may be utilized in this type of transducer 30.4, and also additional stacks of sheet magnets and diaphragms may be applied to this transThe transducer 30.5 illustrated in HG. 10 is substantially the same as that illustrated in HGS. 1-4, except that in this form of tile transducer, the frame and spacer strips 32.5 are ^f®^d S ^^^^{8 &lt;}5^rect,y.^to.tiie perforated, flexible sheet . _ -----------invention, tiie frame and spacer strips 32.5 hold the flexible sheet magnet 34.5 taut and therefore the sheet magnet is stiff to be restrained from undesired movement or flexing. The flexible sheet magnet has many times the mass and thickness of the diaphragm 31.5 so . , · ------- current signals are applied to the conductors 36.5, the diaphragm will vibrate to effect sound generation and the sheet magnet 34.5 remains essentially stationary.

As an optional aspect of the transducer 30.5 of HG 10 a ⁵ second, stacked diaphragm 31.5' is applied under tension and becau. the flexible sheet magnet 34 lies flush ag^T^ 70 ffiZhTLTofr^XlS mTraeU fi’T ? “T Τ’ ^{therefore the} ‘° the conductors L magnetic fields along the zones of the sheet magnet 34 are optimized essentially uniform so as to contribute materially to the uniformity of the vibration of the diaphragm across its entire vibratable area.

3,674,946 stretched to the frame strip 32.5 at the opposite side of the sheet magnet 34.5 from the diaphragm 31.5. The diaphragm 31.5' also carried conductors 36.5' which will ordinarily carry the same signal carried by conductors 36.5 so that the two diaphragms work together in producing the sound.

It will be noted that in the transducer 30.5, the magnetic fields of the magnetized zones or bands in the sheet magnet 34.5 at both sides of the sheet magnet are utilized. In the event that the second diaphragm 31.5' is omitted, the flexible sheet magnet may be magnetized in the manner illustrated in FIG. 29 wherein the magnetic fields from the zones or bands exist predominantly adjacent the upper surface of the sheet magnet.

In the form of the transducer 30.6 illustrated in FIG. 11, the diaphragm 31.6 is secured by spacers 32.6 and 32.6' directly to the flexible sheet magnet 34.6. Although the spacer strip at the periphery of the magnet and diaphragm 32.6 are ordinarily substantially rigid, they may be flexible so that the transducer 30.6 may assume a somewhat non-planar configuration. The vibratable area 31.6α is maintained in spaced relation with the confronting area of the flexible sheet magnet 34.6 by the spacers 32.6' which are small dots or cylindrical plugs of soft and yieldable material such as foam rubber or batted cotton fibers.

Although the spacers 32.6' restrict the large excursions of the diaphragm, the speaker generates a substantial energy output in the form of sound power. In this same general arrangement, the conductors may be stacked on each other and additional diaphragms may be stacked onto the rear side of the flexible sheet magnet 34.6.

The transducer 30.7 of FIGS. 12,14 and 15, have a greatly enlarged diaphragm area for the purpose of very substantially increasing the quality and energy output of the speaker. This speaker frame 32.7 defines an overall interior opening 32.7α approximating 8 inches by 5 feet in dimensions, and the length of the opening may be extended to 10 feet to further increase the energy output. In this embodiment, it is contemplated that the transducer 30.7 may be incorporated into an upright panel structure which may be utilized as a room divider in a home or as a space divider in any other type of interior arrangement. The frame 32.7 may be constructed of rigid metal or rigid sheet plastic such as styrene, and the diaphragm 31.7 is tensioned and stretched in both longitudinal and transverse directions as it is secured by adhesive to the frame 32.7. Stretching in only one direction is also satisfactory. The pole piece panel 35.7 is also affixed to the rear side of the frame 32.7 and has an overall shape very nearly the same as that of the frame. The perforate flexible sheet magnet 34.7 extends, in this embodiment, throughout the entire length of the opening 32.7α and lies flush against the pole piece panel 35.7.

The diaphragm 31.7 is divided into a number of separate vibratable areas 31.lb, 31.7c, 31.7d, 31.7e and 31.7/, each of which has a different length and area as compared to each of the other vibratable areas. The several vibratable areas are defined by a plurality of rigid spacer strips 37.7 adhesively secured to the diaphragm and also to the top of the sheet magnet 34.7. The portion of the diaphragm which overlies each of the strips 37.7 is prohibited from vibrating, and therefore each of the vibratable areas 31.76—31.7/ vibrates independently. Because of the different sizes of the vibratable areas 31.76-3 1.7/ each of these vibratable areas has a different set of resonant frequencies.

The conductors 36.7 extend throughout the length of the entire diaphragm and traverse the separate vibratable areas so as to apply the same signals to all of the diaphragm areas.

The pole piece panel 35.7 and the sheet magnet 34.7 are dished or panned adjacent each of the separate vibratable areas of the diaphragm.

In FIG. 13, which is a frequency response chart for the transducer 30.7, the curve C represents the frequency response chart for the vibratable area 31.7c. The peak C' of the curve C indicates the resonant peak produced at the fundamental resonant frequency of the particular vibratable area with which this individual frequency response curve is related. Each of the other vibratable areas has its resonant peak occurring at a different frequency, because of the difference in the areas of the diaphragm, and the separate resonant peaks are illustrated in dotted lines and denoted by letters b, d, e and /. It will be noted that the typical frequency response chart for the area 31.7c shows a decline in the output at frequencies just above the resonant peak, and then at progressively higher frequencies, the energy output from the diaphragm area progressively increases. Because of the averaging effect of the several vibratable areas of various sizes and the effect of their respective resonant peaks, the overall frequency response curve for the transducer 30.7 is relatively constant across the spectrum of audio frequencies as is indicated by the curve A.

It will be understood that the sound reproduction from a transducer having a multiplicity of various sizes of vibratable areas is far superior than the sound reproduction from a speaker or transducer having a single vibratable area.

FIG. 16 illustrates an alternate construction as compared to that illustrated in FIGS. 12,14 and 15. The transducer 30.8 of FIG. 16 has the vibratable areas of the diaphragm separated from each other by an integral portion or divider bar of the frame 32.8, instead of the spacer strip illustrated in FIG. 14. The frame 32.8 is attached directly to the panel 35.8 of magnetic material, and, as in the transducer 30.7, the pole piece panel 35.8 is panned or dished opposite each of the vibratable areas of the diaphragm. In FIG. 16, the flexible sheet magents 34.8 are sized to conform to the size of the particular vibrata₃₀ ble areas and lay against the pole piece panel 35.8.

Of particular importance in the transducer 30.8 of FIG. 16, the conductors 36.8 do not traverse from one vibratable area of the diaphragm to the other vibratable areas, but are isolated so that different signals can be applied to the conductors at ₃₅ different vibratable areas of the diaphragm. The output signal from an audio amplifier may be applied to a crossover network or a divider network so as to separate various frequencies in the signal from each other, and the various frequencies can be applied to the conductors of the various vibratable 40 ^areas of the speaker to obtain an improved speaker operation, specifically improved frequency response, greater energy output, less distortion, and better polar distribution.

In a modified form of the transducer 30.8 of FIG. 16, the divider bar 32.8 between the adjacent vibratable areas of the 45 diaphragm may be entirely eliminated such that the elongate diaphragm is only secured to the frame and perforate plate 35.9 at the periphery of the diaphragm as a whole. The separate conductors 36.8, being isolated from each other, define the vibratable areas of the diaphragm, and, as hereinbe50 fore described, the several vibratable areas of the diaphragm may have different sizes so as to be resonant at various frequencies. It may be desirable to apply the same electric signals to the conductors of all of the vibratable areas; and it may otherwise be desirable to separate the various frequencies of the signal from each other by means of a cross-over network or divider network so as to apply the high audio frequency signals to the smaller vibratable areas of the diaphragm, and apply the lowest range of audio signals to the conductors’ of the largest vibratable area of the diaphragm, and the midrange audio frequency signals to the conductors of a vibratable area of intermediate size. In dividing the diaphragm into separate vibratable areas for receiving separated portions of the audio frequency signal, it is generally proven satisfactory to divide the diaphragm only into three separate areas. In the alternate form of transducer which eliminates the divider bar 32.8 of the frame, the perforate sheet metal panel and the sheet magnet may be dished relative to the diaphragm as a whole rather than in relation to each of the vibratable areas; i.e., the metal panel and sheet magnet do not converge toward the diaphragm in a direction longitudinally of the transducer as a whole and at the boundaries of the separate vibratable areas defined by the conductors on the diaphragm.

A form of speaker similar to the described variation on FIG 16 wherein the divider bar 32.8 of the frame is eliminated is illustrated in FIGS. 30 and 32.

3,674,946

In the transducer 30.9 of FIGS. 17 and 18, the frame 32.9 defines a plurality of substantially equal size openings 32.9a The diaphragm 31.9 traverses the entire frame and is tensioned in both longitudinal and transverse directions, but need be tensioned in only one direction. The conductors 36 9 on each of the separate vibratable areas of the diaphragm are isolated in relation to each other so that different signals can be applied to the conductors of various vibratable areas after the frequencies have been separated in a divider network or similar circuit.

In the transducer 30.9, each of the vibratable areas of the diaphragm is affixed to a rigid spacer strip which may be constructed of cardboard or styrene, or a similar material and which is indicated by the numeral 38.9. These strips 38 9 are located at different locations in each of the openings of the frame and adjacent each of the vibratable areas of the diaphragm. The strips 38.9 prevent the diaphragm from vibrating at the point of connection so that at each of the openings 32.9a of the frame, the vibratable diaphragm is Divided into two separate areas. The relative sizes of these ^:vibratable areas in each of the frame openings is different as can be observed in FIG. 17. These various sizes of vibratable areas of the diaphragm result in varying resonant frequencies for these various vibratable areas and, as a result, a smooth overall frequency response is obtained from the transducer

As illustrated in FIG. 19 which is an alternate form, a variation on the transducer 30.9, the transducer 30.10 of FIG. 19 may have the conductors 36.10 arranged to traverse between the separate areas of the diaphragm and traverse the diaphragm from one opening in the frame to another. In FIGS. 20 and 21, as in the other forms of transducers, the proportions of the sizes of the elements are somewhat disproportionate in order to make them clearly visible and understandable in the drawings. The spacings and the conductor thicknesses as well as the diaphragm thicknesses must be considered to be relatively diagrammatic.

Another variation of the transducer 30.9 has a different tension and a different degree of stretching at each of the vibratable areas of the transducer; it may be necessary that the several vibratable areas of the diaphragm be separated from each other so that they can be individually tensioned and stretched, and where the tension at each of the vibratable areas is varied relative to each other, the strips 38.9 need not be utilized. The difference in tension on the several vibratable areas changes their relative resonant frequencies so as to increase the uniformity of the output of the transducer substantially across the range of audio frequencies.

The transducer 30.11 of FIGS. 20 and 21 has a frame 32.11 with several different sizes of openings 32.11α, 32.116, 32.1 lc. The proportions of these openings vary with respect to each other so as to vary the sizes of the vibratable areas of the diaphragm 31.11. The openings as seen in FIG. 20 are approximately 8 inches wide and the smallest of these openings 32.11c is approximately 1 inch long and the largest opening 32.116 is approximately 10 inches long. As a result of substantially uniform tension on all portions of the diaphragm, the various vibratable areas of the diaphragm are stretched substantially uniformly. The conductors 36.11 traverse all of the vibratable areas of the diaphragm, and, of course, because the vibratable area 31.116 is the largest of the three vibratable areas, the maximum excursion of the diaphragm will be effected, so as to maximize the energy output of at least the low audio frequency signals. The smallest of the vibratable areas 31.11c will have high energy output for the high frequency audio signals, and particularly a higher energy output than produced by the other two vibratable areas for these high range audio frequencies. It will be particularly noted in this speaker that the perforate flexible plastic sheet magnet 34.11c has a lesser proportion of open area because of the wider spacing of the perforations 34.11' therein; and, furthermore, the sheet magnet 34.11c is considerably closer to the vibratable area 31.11c of the diaphragm than is the perforated plastic flexible sheet magnet 34.116 from its corresponding vibrata10 ble area of the, diaphragm. The pole piece panel 35.11 has opeiunes 35.11' corresponding to the spacing of the openings 34.11 , and a supplemental pole piece panel 35.11α lies flush against the pole piece 35.11 and also flush against the bottom surface of the sheet magnet 34.1 lc so as to act as a part of the pole fuece panel 35.11 in its effect upon the magnetic fields in the sheet magnet 34.1 lc.

Because of the close spacing between the sheet magnet , « , ^{the vibratable} 31.11c and the conductors 3o.ll thereon, and also because of the reduced proportion of open area of sheet magnet 34.11c, the magnetic field is stronger at the conductors and therefore the field generated by the current passing through the conductors has a greater effect upon the diaphragm so that a higher energy output from the vibratable area 31.11c of the diaphragm is produced, especially at the higher audio frequencies.

The effect of the different sized vibratable areas of the diaphragm 31.11 in transducer 30.11 is to improve the speaker operation as emphasized in connection with transducer 30.8 in FIG. 16. The sound output from the vibrating diaphragm of these flat transducers or speakers is relatively directional when the dimensions of the generating source are large as compared to the wave length of the signal, and therefore the use of relatively small vibratable areas of the diaphragm such as vibratable area 31.11c for the high range audio frequency sounds, and the large size vibratable area 31.116 for the extremely low range of audio frequency sounds and the intermediate sized vibratable area 31.11α for the midrange audio frequency sounds, has the effect to improve the P°l^ distribution of all the sounds produced by the transducer

The polar distribution obtained with a transducer of the nature illustrated in FIGS. 20 and 21 is quite satisfactory.

In order to increase the energy output at the several vibratable areas of the diaphragm, the transducer 30.12 illustrated in FIG. 22 may be utilized, and this transducer is a variation on the form of transducer 30.11 shown in FIGS. 20 and 21. In this transducer, the conductors 36.12c on the smallest vibratable area 31.12c are separate from and of considerably less mass than the other conductors on the other vibratable areas of the diaphragm, such as the conductor 36.126 which is affixed on the largest vibratable area 31.126 of the diaphragm. The reduced mass of the conductor 36.12c permits the vibratable area 31.12c to respond to the high range audio frequency signals which are applied thereto and which have been separated from the audio signal as a whole by a suitable divider network or equivalent circuitry. This arrangement of separate conductors on the various sized vibratable areas and the use of an extremely light conductor, such as a one-quarter mill foil, on the smallest vibratable area of the diaphragm produces a highly satisfactory output from the transducer 30.12. It will be understood that in both the transducers 30.11 and 30.12, the reduced open area in the flexible plastic sheet magnets 34.1 lc and 34.12c, the magnetic fields of these magnets can be stronger so as to have a greater effect upon the vibrating of the diaphragm areas. A separate piece of thinner, lighter diaphragm material may be substituted as the vibratable area 31.11c to further increase the energy output of high audio frequency signals.

As previously described in connection with FIG. 16, a variation on the transducer 30.12 illustrated in FIG. 22 would be the elimination of the crossbar 32.12 of the frame so that the diaphragm is attached to the frame only at the exterior periphery, and the several vibratable areas of the diaphragm are defined only by the conductors carried by the diaphragm. Each of these vibratable areas of the diaphragm will vibrate substantially independently of each other, according to the signal applied to the respective conductor. Of course, highly satisfactory polar distribution is obtained with this variation of the transducer.

Another variation of the transducer 30.12 of FIG 22 is the use of conductors 36.12c which are considerably narrower than those illustrated and considerably narrower than the con10

3,674,946 ductors used on the other vibratable areas of the diaphragm. These narrower conductors are arranged in runs considerably closer than that illustrated and considerably closer together than the relative spacing between adjacent runs on the other vibratable areas of the diaphragm; and similarly, the magnetic zones in the sheet magnet are considerably narrower and have closer spacings, as to conform to the width and spacing of the conductors on the diaphragm. As a result, the high frequency output of this vibratable area of the transducer is increased.

This same variation in width and spacing of conductors on the diaphragm and of the magnetic zones in the sheet magnet may also be used even though the spacer bar 32.12 of the frame is eliminated as hereinbefore described in the previous variation.

Another form of transducer is shown in FIGS. 23 and 24 and is indicated by the numeral 30.13, and the transducer is substantially cylindrical in shape. The frame or spacer strip 32.13 is substantially cylindrically shaped, as is the pole piece panel 35.13. This pole piece panel 35.13 is dished slightly between its edges so that the central portion thereof is spaced from the diaphragm 31.13 to a greater extent than the edges of the pole piece panel. The diaphragm 31.13 is substantially cylindrical in shape, and carries the conductors 36.13 in conformance with the shape of the magnetized zones or bands of the perforate flexible plastic sheet magnet 34.13. The diameter of transducer 30.13 may be on the order of 12 inches or more. High frequency transducers of this type may be considerably less than 12 inches in diameter.

Of course, the polar distribution of the transducer 30.13 is 30 very satisfactory because the energy output emanates in substantially all directions.

In the transducer 30.14 illustrated in FIG. 25, stacked flexible sheet magnets 34.14a and 34.14b are disposed on opposite sides of a common diaphragm 31.14 carrying conductors 35 36.14 This arrangement of stacked sheet magnets substantially increases energy output and minimizes problems of modulation distortion that may occur in transducers using a single sheet magnet and wherein the vibratable area of the diaphragm may move toward and away from a single magnet 40 at low frequencies has a decided effect upon the linearity of output of high frequency signals being simultaneously produced. In this transducer 30.14, as the diaphragm moves at low frequencies the magnetic fields from the two stacked sheet magnets remains substantially constant regardless of the ⁴⁵position of the diaphragm so as to minimize distortion of high frequency signals being simultaneously produced.

A variation of the transducer 30.14 of FIG. 25 is the substitution for diaphragm 31.14, of a pair of parallel diaphragms confronting each other and spaced slightly from each other. A spacing of 0.020 inches is satisfactory (for purposes of comparison, the metal panel 35.14 is illustrated to be approximately 0.050 inches in thickness as is the metal panel 35 in FIGS. 2 and 3). Both of the diaphragms in this variation will be stretched, but may have different tensions applied relative to each other; both diaphragms will carry conductors, although the number and size of conductors may vary relative to each other quite considerably, for instance, one conductor may carry stacked conductors and thus be relatively heavy, and the other diaphragm may carry only very small and thin conductors to be highly responsive to high frequency signals.

In the transducer 30.15 illustrated in FIGS. 26 and 27, the diaphragm 31.15 has conductors 36.15α and 36.15b on the upper and lower surfaces thereof. The conductors 36.15α are 65 in runs which extend transversely of the runs of conductors 36.15b. Both of the upper and lower conductors 36.15α and 36.15b carry the same signal, and the effect is to produce vibrating movement of larger areas of the diaphragm which may tend to remain stationary in the open spaces between the 70 conductors. The magnetized zones or bands in the perforate flexible plastic sheet magnet 34.15α extend parallel to the runs of conductor 36.15α on the top side of the diaphragm; and the elongate magnetic bands or zones in the lower magnet 34.15b extend parallel to the runs of conductor 36.15b. Because of 75 the transverse orientation of the magnetic zones or bands in the opposite sheet magnets 34.15α and 34.15b, there is essentially no interaction between these magnetic zones or bands, and the magnetic zones or bands in the sheet magnet 34.15α has essentially no effect upon the fields produced by current flowing in the lower conductors 36.15b; and the magnetic fields resulting from the magnetic bands or zones in the sheet magnet 34.15b has little or no effect upon the fields produced by current flowing in the upper conductors 36.15α.

The overall effect of this transducer is to reduce distortion and increase the energy output as the result of a predetermined signal input because larger areas of the diaphragm 31.15 are set into motion because of the crisscross arrangement of the conductors. This arrangement has particular advantage in transducers using a relatively loose diaphragm, as may be used in small sized transducers.

FIG. 28 is illustrative of the manner in which the perforate flexible plastic sheet magnet 34 is magnetized. Strong magnets 40 are positioned above and below the sheet magnet 34 so as to set up magnetic fields in the sheet magnet in a direction through its thinnest dimension. The pole faces produced at adjoining zones or bands and at the face of the magnets are opposite as indicated by the letters N and S. In this sheet magnet, the magnetic field is detectable at both the top and bottom sides of the sheet magnet.

In FIG. 29, an alternate mode of establishing the magnetized zones or bands in the sheet magnet 34' is illustrated. Conductors 41 are arranged in the configuration of the zones or bands to be produced in the sheet magnet 34', and then the conductors and sheet magnet are brought into proximity with each other so that the electric fields produced by large currents flowing in the conductors create magnetic fields in the sheet magnet 34' such that the magnetic fields exist predominantly at the top surface of the sheet magnet 34' and only minimally at the lower surface.

The elongate transducer 30.16 of FIG. 30 has the diaphragm attached to the spacer strip and to the rigid metal plate only at the periphery of the diaphragm. The conductors 36.16 are secured to the diaphragm 31.16 as previously described. Of course, the magnetic zones of the sheet magnet beneath the diaphragm conform in shape and spacing to the configuration of the conductors 36.16 on the diaphragm. The diaphragm is pulled taut in a direction longitudinally of the transducer, merely to remove the wrinkles from the material of the diaphragm; and the diaphragm is tensioned in a direction across the width of the diaphragm such that the tension in this transverse direction progressively increases from one end of the transducer to the other. As depicted in the graph of FIG. 31, the tension at location A of the diaphragm is relatively low and is preferably only that which is required to remove wrinkles from the diaphragm material. At location B at the opposite end, the tension across the width of the diaphragm is substantially that described in connection with HGS. 1-4 or slightly greater than that amount, and at locations between the opposite ends of the diaphragm, the tension and stretching of the diaphragm progressively varies such that the tension gradually increases in a direction from location A to location B. As a result of the varying tension, the various portions of the diaphragm are resonant at various sets of frequencies to obtain the advantages described in connection with FIGS. 12-14, so as to obtain substantially uniform output across the full range of audio frequencies.

It will be understood that the width of the conductors on the diaphragm is proportionately less than that illustrated in the drawing, because of the practical considerations in actually making the ink drawing, and, likewise, the number of runs of conductor is considerably greater than that illustrated in the drawing. In FIG. 30, the diaphragm has only a single vibratable area. It may be desirable to isolate a small number of runs of the conductor adjacent one of the longitudinal edges to receive the high range audio frequency signals so as to effect desirable polar distribution of the high frequency audio sounds produced. Similarly, a number of runs of the conduc10

3,674,946 tor adjacent the opposite longitudinal edge may be isolated and used to carry the mid-range audio frequency signals from the divider network; and to apply the low range audio frequency signals to the remainder of the runs of conductor on the diaphragm.

Similarly, in FIG. 32, the transducer 30.17 has the diaphragm 31.17 connected to the spacer strip and perforate panel only at the periphery of the diaphragm. The conductors 36.17α and 36.176 are isolated from each other and are applied to the opposite end portions of the diaphragm. The two conductors will receive the audio output signals from the two channels in a stereophonic system so that the sound will appear to emanate from various portions of the transducer 30.17 as is desirable in such stereo systems. The diaphragm 31.17 relies solely on the separate conductors 36.17α and 36.176 for defining the separate vibratable areas producing the different audio outputs of the stereo system.

It is contemplated that the transducer 30.17 has a size commensurate with that of transducer 30.7 of FIG. 12 and transducer 30.9 of FIG. 17; but it will be understood that this dual channel transducer 30.17 may be constructed in a smaller size for use in earphones of headsets, it being understood that with a separate transducer 30.17 in each of two earphones of a headset, four different channels are available for reproduction 25 of sound from suitably recorded magnetic tapes from which such signals are reproduced.

Transducers 30.18 and 30.19 of FIGS. 33 and 34 are illustrative of different conductor and vibratable area arrangements to provide multiple channels on one diaphragm and 30 wherein the vibratable areas are only defined by the existence of isolated conductors which are connectable to the sources of electric signals related to multi-channel systems. As suggested in transducers 30.18 and 30.19, the multiple channel signals and vibratable areas may be utilized for reproducing sound 35 from an original source so as to reproduce the sound to get a feeling of height as well as a feeling of horizontal spread between the sources of the sound.

It will be seen that I have provided a new and improved electromagnetic transducer in the shape of a flat panel and 40 without any appreciable depth as compared to its length and breadth, and which may be readily and easily manufactured because of the simple nature of materials used. The use of the flexible plastic sheet magnet, perforated to the desired degree, minimizes any gap consideration between the sheet magnets ⁴⁵and the pole piece panels against which the sheet magnets lie, and without any machining or smoothening of the abutting faces of the sheet magnets and pole piece panels. These electromagnetic transducers can be constructed in many different shapes and configurations to increase the energy output as by stacking the conductors on the diaphragms, stacking the diaphragms on both sides of the magnetic panels, and providing for close spacing between the diaphragm and the sheet magnet by dishing the magnets to accommodate large excursions of diaphragm movement near the center of the vibratable areas while the spacing between the sheet magnet and the diaphragm adjacent the edge of the vibratable areas remains at a minimum. These electromagnetic transducers can be constructed to produce smooth frequency response charac- gQ teristics and to produce very satisfactory polar distribution of the energy output.