Sound reproducer

July 28, 1959 _{A BURKE} 2,897,291

SOUND REPRODUCER Filed Dec. 12, 1955

<img file="US2897291A_D0001.tif" />

-Atty.

United States Patent Office

2,897,291

Patented July 28, 1959

2,897,291

SOUND REPRODUCER Ambrose Burke, Scituate, R.I.

Application December 12,1955, Serial No. 552,315

Claims. (Cl. 179—115.5)

This invention pertains generally to sound reproducers, and more specifically, to a loudspeaker of the electrodynamic or moving-coil type.

A primary object of the instant invention is the provision of a loudspeaker which will supply more harmonics or overtones than heretofore, thereby providing sound which, in effect, appears to be more three dimensional in scope and less flat than sound reproduced by conventional speakers heretofore utilized.

Another object of the instant invention is the provision of a loudspeaker capable of utilizing a greater output from a transformer while at the same time producing sharp and distinct tones.

Still another object is the provision of a speaker which has virtually no resonant frequency such as usually caused by cone vibration, and which smooths out and reduces the gain or such caused by an audio frequency.

A further object is the provision of a speaker which is exceedingly effective at low frequencies.

Another object of the instant invention is the provision of a loudspeaker which, although simple of construction, is nevertheless highly efficient and sensitive in operation.

Other objects, features and advantages of the invention will become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.

In the drawings which illustrate the best mode presently contemplated by me for carrying out my invention:

Fig. 1 is a front elevation of a loudspeaker embodying the instant invention;

Fig. 2 is a rear elevation thereof, partly broken away;

Fig. 3 is an enlarged section taken on line 3—3 of Fig. 2; and

Fig. 4 is detail section, partly broken away, of the outer armature utilized in the instant invention.

The conventional electrodynamic loudspeaker or sound reproducer as heretofore utilized, has worked on the principle of a moving voice coil, which, when excited, usually by magnetic means, imparts vibration to the speaker cone thereby producing sound. More specifically, the moving voice coil is usually wound on a cardboard bobbin or the like which in turn is secured to the speaker cone. A magnetic field is provided proximate to said voice coil and the electrodynamic action which results between the flux produced by current passing through the wires of said coil and the magnetic lines of force creates a mechanical upward and downward pulling action. This force causes the voice coil to move up and down, which in turn makes the speaker cone vibrate and produce sound. The volume from the speaker is determined by the strength of the magnetic field, the number of turns in the voice coil, and the amount of current passing therethrough.

It has been found that the above-described speaker operation can be greatly improved by the use of double voice coils, concentrically disposed. By setting up the two coils so that, they each coact with separate and independent magnetic fields and function in unison, the sound output is .

more sharp and distinct, at low frequencies as well as high ones.

Referring now to the drawings, a loudspeaker constructed in accordance with the instant invention is shown 5 generally at 10. Speaker 10 comprises a metallic conical shell 12 having a peripheral flange portion 14. Secured to flange 14, as by a fiber clamping ring 16 or the like, is a paper speaker cone or diaphragm· 18 of conventional construction. The truncated end 20 of cone 18 has se10 cured thereto by any desirable means, such as cementing, an outer voice coil bobbin 22 comprising a cardboard or aluminum cylinder 24 having windings 26 therearound. A cork or composition ring 28 is secured to the inner surface of the cylinder 24 and acts as both spacing and 15 insulating means between outer coil bobbin 22 and an inner voice coil 30, likewise comprising a cardboard or aluminum cylinder having windings therearound. It will be understood that the voice coil bobbin 30 is secured to the spacer 28 and is maintained solely thereby in con20 centric relation with respect to outer voice coil bobbin 22. It will further be understood that the bobbins 22 and 30, other than the former’s connection to speaker cone 18, are not anchored in any way and hence are free to move axially whereby to impart vibration to the speaker 25 cone 18.

Secured to the truncated end of shell 12 by any desirable means, as at 32, is a metallic rectangular supporting strap 34. Supporting strap 34 comprises a rear wall 36, side walls 38 and a front wall 40 having therein a 30 centrally disposed aperture 42, the inner surface 43 of which comprises a pole face. Mounted on the inner surface of rear wall as by cementing or .the like is a permanent magnet 44, although it will be understood that other forms and types of magnets, such as an electromag35 net, for example, could well be utilized. Magnet 44 at its free forward surface engages inner and outer poles 46 and 48, respectively, now to be described. It will be understood that poles 46 and 48 are each constructed of magnetic steel and hence, due to their contact with magnet 40 44, provide their respective magnetic fields. The outer pole 48 comprises a tubular body portion 50, the outer diameter of which extends through the aperture 42 in spaced relation to pole face 43 thereof whereby to provide a gap 51. Pole 48 further comprises an outwardly 45 extending peripheral flange 52 which is in contact with magnet 44. Inner pole 46 comprises a core portion 54, and likewise is provided with an outwardly extending flange 56. As will be noted, inner pole 46 is mounted concentrically within outer pole 48 by virtue of the fact 50 that flange 56 is a press-fit therein. A circular spacer ring 57 of non-magnetic material, such as brass, maintains outer pole 48 against longitudinal movement, and also maintains poles 46 and 48 centered with respect to the aperture 42.

In operation and use, outer voice coil bobbin 22 surrounds outer pole 48 in very close proximity thereto and extends into gap 51, while inner voice coil bobbin 30 is disposed intermediate core 54 of the inner pole and tubular portion 50 of the outer pole. As will be noted clearly 6o in Fig. 3, tubular portion 50 does not extend inwardly of gap 51, thereby leaving uncovered a substantial portion of the windings on bobbin 30. As will hereinafter become apparent, this relation is important in that it enables vibrations from one bobbin to be imparted to the other, ₆₅ whereas , if said tubular portion extended in appreciably farther, it would tend to isolate the two bobbins with respect to each other.

It has been found that much improved sound characteristics are achieved in my specific structural arrange70 ment by providing a non-magnetic coating 58 on the inner surface of tubular portion 50. It will be understood that this coating may be of any material which is incapable

2,897,291 of being magnetized or attracted by a magnet, some examples of such material being so-called white metal, brass, aluminum, copper, etc.

Another important feature of the instant invention resides in the fact that the space 59' between voice coil bobbins 22 and 30 acts, in effect, as a sound-compression chamber. In other words, the sound vibration waves which emanate from the outer bobbin 22 will be carried across the chamber 59 and imparted to the inner bobbin 30 and vice versa. Hence, in effect, each voice coil bobbin cooperates with the other to produce more pronounced vibration of the speaker cone. In this respect, it might be pointed out that the windings on either bobbin 22 or 30 could be eliminated, and the loudspeaker would still function in improved fashion. More specifically, if, for example, the windings 26 of outer bobbin 22 were eliminated, the vibrations emanating from inner bobbin 30 would still move across chamber 59 and be imparted to the cylinder 24, thereby causing the latter to aid in vibrating the speaker cone.

Conventional terminals 60 and 62 and wiring 64 and 66 are provided for the energization of the voice coils. Also, a conventional spider 68 may be utilized, if desired, to help maintain the voice coils in proper position and also to act as a dust shield. In fact, it will be understood that the entire construction of the speaker assembly set forth and described herein is of a conventional nature with the exception of the double voice coils and the inner and outer poles described above.

While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept. For example, it would be a simple matter to re-design the poles so that they would be movable with the speaker cone 18, while the voice coil bobbins, in turn, would be fixedly mounted. Therefore, the instant invention is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.