US3449531A

US3449531A - Electro-mechanical transducer

Info

Publication number: US3449531A
Application number: US696632A
Authority: US
Inventors: William J Ashworth
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-01-09
Filing date: 1968-01-09
Publication date: 1969-06-10
Anticipated expiration: 1986-06-10

Description

June 10,l 1969 W- J- ASHWORTH 3,449,531

ELECTRO-MECHANICAL TRANSDUCER Filed Jan. 9, 1968 Shee'fI FIG.

FIG.5

F I G. 7

June 10, 1969 w. J. Asl-:WORTH ELECTRO-MECHANICAL TRANSDUCER Filed Jan. 9, 1968 Sheet .2 of 2 .93 56 6 7 VAWNNNNNNWA e .4

4 slwe O 6 A M3 6 6 `W s: 2 6 4 5 u 4 6 FIG. 9

FIG. 8

FIG.

INVENTOR wmgwm FIG.

United States Patent O 3,449,531 ELECTRO-MECHANICAL TRANSDUCER William J. Ashworth, Rte. 2, New Albany, Miss. 38652 Filed Jan. 9, 1968, Ser. No. 696,632 Int. Cl. H04r 7/02 U.S. Cl. 179--115 9 Claims ABSTRACT F THE DISCLOSURE A sound system using a transducer or sound reproducer, having a radiating exible diaphragm which is attached to a sounding board, for example, walls, doors, car body, etc., causing the sounding board to radiate sound. The electromagnet driving member is resiliently attached to the armature so that the armature and driving members are capable of relative, interacting motion and are thereby capable of good low frequency response as well as a good mid range and high frequency response. The resilient mounting can be accomplished by either springs or resilient pads. Besides sound reproduction, other uses for the sound reproducer are available.

Background of invention This application is a continuation in part of my copending application, Ser. No. 541,209, filed April 8, 1966 and entitled Combination Momentum and Inertia Sound Reproducer, now abandoned.

The present invention relates to a magnetically activated transducer, useful particularly in the production of sound and is particularly designed as a transducer unit to be attached to a sound radiating source or sounding board such as a wall, door, or car body, for example.

Heretofore, other electrical sound reproducing devices of the same general type as that described above, have been proposed, for example, that shown in my prior U.S. Patent 3,178,512, issued Apr. 13, 1965, and my U.S. Patent 3,334,195, issued Aug` l, 1967 but will have had response of only moderate fidelity.

Summary of invention The present invention solves the low frequency response problem by a unique resilient suspension system whereby the electromagnet driving member and the armature member are capable of relative, interacting motion and permit mutual power transfer between the two. Many reiinements and improvements utilizing the unique transducer of the present invention have been devised and are disclosed and claimed below.

Other objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings.

Description of the drawings FIG. 1 is an end elevation view of one embodiment of the present invention.

FIG. 2 is a side elevation view of another embodiment of the present invention.

FIG. 3 is a front elevation of a further embodiment of the present invention.

FIG. 4 is an elevation view of a still further embodiment of the present invention.

FIG. 5 is an elevation view showing an alternate construction of the present invention.

FIG. 6 is a sectional view taken along line x--x of FIG. 5.

FIG. 7 is an elevation view of the present invention showing a further alternate construction.

FIG. 8 shows a method of using the present invention n combination with a loudspeaker.

3,449,531 Patented June 10, 1969 ICC FIG. 9 shows another method of using the present invention in combination with a loudspeaker. FIG. 10 shows a further method of using the present lnvention in combination with a loudspeaker.

FIG. 11 shows a still further method of using the present invention in combination with a loudspeaker.

Description of the preferred embodiments An electromagnet 10 is mounted on the lower side of upper plate 13, substantially centered with plate 13 and comprises a laminated E shaped frame or core 11 having three equally spaced arms or poles and on the center arm or pole 11 of which is mounted an electrical winding, comprising a coil 12, whereby the electromagnet may be energized when the coil leads 51 are connected to a signal source.

The diaphragm 15 is non-rigidly or flexibly attached to the upper plate 13 in the following manner. The four screws 19 extend through four equally spaced apertures in the upper plate 13 parallel with the legs of the E frame core 11 and the lower ends of the screws 19 are connected to the upper ends of four coiled spring 18 made of brass. The opposite ends of the four brass springs 18 are firmly connected to the upper face of the diaphragm 15. As shown, the four screws 19 are longitudinally adjustable in the four apertures of plate 13 by means of locknuts 20 threaded onto the screws 19 one on each side of the upper plate 13.

The function of the adjustable screws 19 are to adjust the spacing between the diaphragm 15 and the pole pieces of the electromagnet. This spacing is critical for optimum performance. The closer the armature is positioned to the electromagnet pole pieces the greater is the efliciency of operation. However, if the armature spacing is too close to the electromagnet pole pieces, metal to metal contact between the armature and the pole pieces will result.

On the other hand, if the armature is spaced too far away from the electromagnet pole pieces, the eilciency of the sound reproduced will be considerably lowered. It is extremely ditiicult to maintain this optimum spacing under production conditions. A number of problems complicates the task of maintaining the critical spacing between the electromagnet pole pieces and the armature. If a production parts should slightly vary, the spacing would be incorrect. Tension in various parts could vary and this would require a different spacing between the armature and the electromagnet pole pieces. To overcome the problem of maintaining this critical spacing the system of a1- lowing the diaphragm 15 to be adjusted in or out with the locknuts and the screws was devised. As shown above, the screws 19 are rigidly fastened to brass springs 18 with nuts 21 and are in turn welded to the diaphragm 15. They are supported by the upper plate 13 and held rigidly in place with locknuts 20. Diaphragm 15 is pulled toward core 11 by the pull of the electromagnet and is held in a spaced relationship with the electromagnet core 11 by springs 18. This spaced apart relationship can be adjusted in or out by adjusting locknuts 20 until the opti-mum spacing between the diaphragm 15 and the electromagnet core 11 is obtained. This eliminates the necessity of attempting to maintain very close fixed tolerances in production. This adjustment is especially advantageous to the present invention because of the relatively long movement between the diaphragm 15 and the electromagnet at certain operating frequencies. When the diaphragm 15 of the transducer embodying the present invention is solidly attached to a sounding board 16 such as a door, wall, ceiling, or other object and an electrical signal is fed into lead wires 51 of the electromagnet the transducer will cause the sounding board 16 to vibrate and radiate sound.

At this point it will be realized that as the electromagnet is activated by a variable electrical current passing through the coil 12, the pole 11 will become Variably magnetized and so effect a variable magnetic attraction on the diaphragm 1S thereby imparting vibrations to the sound board 16 onto which the diaphragm 15 is attached.

The brass springs 18 also serve as a resilient restoring means for the normal inactive position of the diaphragm 15 as well as serving as a connector for the spacing means between diaphragm 15 and the electromagnet poles.

An alternate construction of the present invention is shown in FIG. 3. The difference in this construction and the construction in FIG. 1 is in the spacing allowed between the diaphragm 15 and the sounding board 16. The diaphragm 15 and mounting plate 27 are held in a spaced apart relationship by the four equally spaced spacers at the outer edge of the diaphragm 15. When these two plates are fastened together and spaced apart by the spacers 28 they become the dual diaphragm armature assembly. This dual diaphragm armature assembly is connected to the upper plate 13 in the same way and by the same means as the diaphragm 15 in FIG. 1.

A modification of the alternate construction shown in FIG. 3 is shown in FIG. 2 and accomplishes the same result as the dual diaphragm armature assembly as shown in FIG. 3. As shown, an attaching screw 17 is centrally welded to the lower diaphragm 15. Screw 17 serves as an attaching means for solidly attaching the transducer to a sounding board. The head of screw 17 acts as a spacer to hold diaphragm 15 in a spaced relation with sounding board 16.

Due to the weight and inertia of the magnetic core, the coil 12 and the mounting hardware, and because of the flexible resilient mounting means 18, enough weight is present to cause the electromagnet portion of the transducer to remain relatively stable and free from oscillations at operating frequencies above approximately 150 cycles per second. When operating above 150 cycles through approximately 2000 cycles per second, the diaphragm 15 oscillates on its resilient mounting, driving the sounding board structure it is attached to, causing sounding board primary radiating element 16 to vibrate and radiate sound.'

At operating frequencies below approximately 150 cycles per second, inertia no longer holds the mass of the electromagnet structure in a fixed position and at these low frequencies the electromagnet is free to oscillate at a large amplitude with the relatively rigid or relatively heavy sounding board 16 being a restraining medium. Because of this restraining action these intense oscillations of the electromagnet interact with the diaphragm 15 and are transferred to the sounding board 16. These intense oscillations are allowed because no restraining `attachments are connected with the electromagnet assembly other than diaphragm through the flexible mounting 18. The nearer the frequency of the activating electrical signal approaches the natural mechanical low resonant frequency of the transducer mass, the more intense the vibrations become. It is because of these intense vibrations that the momentum of the oscillating transducer mass will transfer enough driving force to the sound radiator 16 as to cause the sound radiator to reproduce good quality bass tones. In the past it has been attempted to cause large heavy surfaces to radiate sound like the described sounding board radiating surface but to obtain any degree of bass response, extremely expensive and large equipment was utilized but with little success because of the natural resistance of a surface to radiate sound with a lower tonal response than its own natural resonant frequency. The present invention has solved this problem by causing extremely intense vibrations to -be imparted to the sound radiating surface 16 in the lower frequency ranges.

In order to reproduce good high frequency tones the constructions shown in FIG. 2 and 3 are utilized. At operating frequencies above `approximately 2000 cycles, the sounding board 16 has difficulty in reproducing these frequencies. At these frequencies, diaphragm 15, when mounted in a spaced relation with sounding board 16 still remains active and continues to radiate a high level of sound to approximately 8000 cycles. The normal spacing between the diaphragm 15 and sounding board 16 used in the present invention was approximately 1/16 inch although this spacing is not critical.

lAs can be seen from the above description, three different functions can be performed by the present invention, the first being to reproduce the mid range frequencies by one means, the second being to reproduce the low frequencies by a second means, the third being to reproduce the high frequencies by a third means. These three means are embodied together in the structure of the present invention.

The present invention will operate either as a low impedance device or as a high impedance device. When used as a high impedance device, the constant D.C. currant present in the activating signal is used to produce a biasing magnetic field. The coil lead wires 51 are connected directly to the plate of an audio amplifier output tube and B+. Such a circuit is not described in this disclosure because it is well known to the art. A constant D.C. currant will flow through coil 12, setting up a constant magnetic field around E frame core. This will in turn pull the diaphragm 15 toward the electromagnet, causing tension in springs 18. When a signal is applied to the output tube of the amplifier, this signal will be superimposed on the direct current that is normally flowing. The varying intensity of the signal will cause the transducer to function as previously described. The magnetic bias is necessary to the proper operation of the transducer. This magnetic bias attracts the diaphragm to the electromagnet. The support screws 19 and springs 18 serve as resilient adjustable spacing means to push the diaphragm away from the electromagnet to provide for the proper air gap between the electromagnet and the diaphragm 15.

In the transducer embodiments, the screws 19 are adjusted to provide a gap of approximately 1/16 inch between the electromagnet pole pieces and the armature assembly.

The diaphragm 15 is preferably a disc made of No. 24 gauge M19 electrical steel, two inches in diameter. The upper plate 13 is a disc made of No. 20 guage soft iron, two inches in diameter. Each of the above disclosed embodiments of the present invention comprises core of an electromagnet made from standard 1/2 inch 29 guage M19 electrical steel E lamination 11 stacked 1/2 inch high. A high impedance coil wound with 4000 turns of No. 38 magnet wire may be used or a low impedance coil of 200 turns of No. 25 wire may `be used. Coiled springs 18 are made of 3 turns of .051 diameter spring brass wire wound in a 5/16 inch outside diameter coil 1/2 inch long.

When it is desired to operate the present invention connected to a step down audio output transformer or to a transistor amplifier where no constant DC current ow will be present, it is necessary to provide the magnetic bias with a permanent magnet added to the electromagnet structure, for example, as in the embodiments shown in FIG. 4 and 5.

It should also be pointed out that the number of turns of wire required for coil 12 will vary for the different impedance ratings of the various kinds of driving equipment the transducer might be coupled to. For example, 200 turns of No. 25 wire wound on a `1/2 inch core of M19 electrical steel laminations will have an inductive impedance of approximately 8 ohms at 400 cycles. For high impedance operation, 4000 turns of No. 38 wire wound on a il/z inch core of M19 laminations will have an inductive impedance of approximately 5000 ohms at 400 cycles.

Another embodiment of the persent invention is shown in FIG. 3. Where a high impedance primary winding 12 and a loW impedance secondary winding 14 is wound on the core 11. The secondary -winding can be used to connect directly to a conventional tweeter dynamic loudspeaker as described and claimed in my Patent No.

E 3,178,512.7Coil 12 shown in FIGS. 1, 2 and 3 can be either a high or a low impedance winding. If a low impedance winding is used, a permanent magnet must be disposed in the magnetic circuit of the electromagnet as described and claimed in my Patent No. 3,358,084.

Different objects and surfaces will reproduce different qualities of sound. The thinner and lighter the material to which the sound reproducer is mounted, the greater will be the volume of radiated sound for a given amount of a signal power. A hollow core door covered with l; inch plywood is easier to drive and requires less driving power than a panel of 3A; inch sheetrock, therefore, the hollow core door will give louder sound than the sheetrock if the same amount of power is applied to the sound reproducer. The same will be true for 1A: inch plywood paneling and 3A inch knotty pine paneling. The lighter and thinner 1A inch plywood ywill produce a greater volume of sound with the same amount of power applied to the sound reproducer than will the inch knotty pine paneling.

The sound radiating material to which the sound reproducer is fastened will govern the sound quality obtainable. The sound reproducer will operate well, however, with most materials except concrete and masonry. The sound reproducer can be attached to the sounding board with the screw 17 in the center of the diaphragm 15 as shown in FIG. 2. The diaphragm 15, FIG. 1, or attaching plate 27 of FIG. 3, may be cemented directly to the sounding board with a suitable cement. A spacing will exist between the diaphragm 15 and the object the sound reproducer is fastened to when the screw 17 is used as the attaching means as shown in FIG. 2. A head on the attaching screw may provide for this spacing.

Another embodiment of the present invention illustrated by FIG. 4 shows a low impedance winding 23 wound on core 22. Two permanent magnets 25 are secured to the upper plate 13 with, for example, epoxy cement. The magnets are magnetized longitudinally and are mounted so that the north poles of the magnets are positioned in the same direction and magnetically bias the electromagnet core 22 and diaphragm 15. The diaphragm 15 is nonrigidly or flexibly attached to the upper plate 13. Additional resilient support means may be used by securing sponge rubber pads 29 between the ends of the magnets 25 and the diaphragm 15. These sponge rubber pads 29 dampen the intense oscillation of the transducer when the input signal to the transducer coincides with the mechanical resonant frequency of the transducer. The sponge rubber resilient pads 29 may :be optional in this embodiment of the present invention.

Core 22 is made from 29 gauge M19 electrical steel 1A: inch wide and 1%6 inches long and the electromagnet core 22 is suitably mounted to the upper plate 13 as by a suitable cement such as epoxy cement. The permanent magnets 25 are made of sintered oriented barium ferrite and are 1 inch long, inch wide and We inch thick.

Another form of the present invention is shown in FIGS. 5, 6 and 7 wherein a core 22 is centrally bonded to an iron cover plate or cap 31. A Winding 23 is wound on the core 22. A ring magnet 30 is bounded with a suitable cement to the inner side of the cover plate 31 which tits over the electromagnet core 22 and coil 23.

A resilient foam rubber ring cushion 29', 3/16 inch thick, is cemented on the lower end of ring magnet 30 and diaphragm 15 is cemented to the cushion 29. Contact cement was found to be suitable for cementing the resilient cushion 29 to the magnet 30 and diaphragm 15.

For adjusting the air gap between the electromagnet core 30 and the diaphragm 15, the upper cover plate 31 has three equally spaced runners 41 welded or formed on its underside which ride on slanting face-cam surfaces 34 molded in the top of ring magnet 30. As shown, the cam surfaces 34 are depressed 716 inch inward at their ends 35, 37, and 39 and gradually rise to the level of the upper end of magnet 30 at their

ends

36, 38, and 40, as

shown in FIG. 6 which is a view taken on line x--x of FIG. 5. When the circular cover plate 31 is placed in position over ring magnet 30 the runners 41 rest on the cam surfaces 34. As can be seen from FIG. 6, if the cover plate 31 is turned clockwise with magnet 30 remaining stationary, the runners 41 Will follow the inward slope of the cam surfaces 34 lowering the cover plate in relation to magnet 30. Because the electromagnet core 22 is bonded to the cover plate it will also move inward as the cover plate is turned clockwise. On the other hand, if the cover plate is turned in the opposite direction, the electromagnet core 22 will move in an outward direction relative to the magnet 30.

It will now be apparent that by rotating the cover plate 31, the air gap between the core 22 and diaphragm can easily be adjusted for the correct spacing. When the proper spacing has been made, the cover plate 31 is then locked in position with screw 32 which extends through the inclined slot 33 in the sidewall of the cover 31 and screws into a threaded hole in magnet 30.

It was found that by moving the steel cover plate 31 which provides the magnetic flux path between the core 22 and magnet 30, away from complete solid contact with the magnet 30 did not affect the performance of the transducer.

Ring magnet 30 was made from sintered non-oriented barium ferrite, l inch high with an outside diameter of 2 inches and an inside diameter of 1 inch.

Another form of the present invention as shown in FIG. 7, has a basic construction similar to that as described for the construction in FIG. 5. In this form a secondary coil 47 is added, consisting of 1,500 turns of No. 38 wire and wound on the electromagnet core 22, which drives an electrostatic operated piezeo element 46. This construction is and claimed in my U.S. Patent 3,358,084. The piezeo element 46 is cemented to the underside of circular diaphragm 45 made of aluminum foil .008 inches thick. Then the piezeo element 46 is activated by the secondary winding 47, it in turn activates the foil diaphragm 45 producing a high level of sound in the high frequency range. Suitable frequency blocking or crossover networks may be used for selecting the frequency range desired for this tweeter section. Suitable networks are described in my U.S. Patent 3,358,084.

For better clarity, the leads from the secondary winding 47 are not shown in FIG. 7 but they are connected to each side of element 47.

As shown in FIG. 7, a spacer ring 49 is cemented on an upper circular plate 43 which carries the runners 41 and engages the cam surfaces 34. The foil diaphragm 45 is cemented to =the upper side of the spacer ring 49 and a second spacer ring 48 is cemented to the upper side of foil diaphragm. A 2 inch circular piece of screen wire 44 is then cemented to the upper side of spacer ring 48 and the entire assembly, comprising

parts

43, 44, 45, 46, 48, and 49, is cemented to the cover 42. By turning cover 42, `the air gap is adjusted between the core 22 and diaphragm as described for the construction shown in FIG. 5.

The construction shown in FIG. 7 utilizes a magnetizable metal surface as a sounding board. Foam rubber cushions 29 cemented to the lower side of ring magnet 30 are placed in contact with the metal sounding board 50. The magnetic attraction between the metal surface 50 and ring magnet 30 will now hold the transducer to the stuface 50 without any other holding means. This type of construction is especially useful when used as u sound reproducing means for automobiles. The foam rubber pads 29 may be cemented to sounding board 50 -When a permanent installation is desired.

A transistor or other type of tiny radio receiver may be built inside the transducer cover. The transducer is then attached to a sounding board and a far better quality of sound can be obtained than can be had with a small loudspeaker, yet the entire mechanism is extremely small.

Another form of my invention is shown in FIGS. 8, 9, l0, and l1. This form is a continuation-in-part of my now copending application, Ser. No. 558,204, tiled June 13, 1966 now abandoned.

The transducer 54 of the present invention and a conventional dynamic loudspeaker S5 are used in combination to form a unique sound system. The advantage of such a sound system resides in the fact that when transducer 54 and loudspeaker 55 are driven by the same Signal, the sounding board 16 activated by transducer 54 and the paper diaphragm of loudspeaker 55 have a difierent decap time. For example, when a given tone is fed to transducer 54 and loudspeaker 55 from amplifier 56 and signal source 57, sounding board 16 and the diaphragm of speaker 55 will be caused to vibrate. When the signal ceases, the vibration decay time of the loudspeaker paper cone will be faster than the decay time of the large sounding board 16. This gives a very pleasing sound sensation to the listener resembling true reverberation. This reverberation effect gives much more realism and is more pleasant to listen to than systems utilizing the spring type units.

There is considerably less distortion present in the system using the transducer of the present invention than in the reverberation systems using the spring type reverberation units such as described in -my U.S. Patent 3,174,- 121.

FIG. 8 shows transducer 54 and a loudspeaker 55 in parallel driven by amplifier 56 actuated by a signal source 57 which may be a radio tuner, turntable, or other signal source. Leads 62 connect the signal source with the ampliter and leads 63 and 64 connect the amplifier output with the

sound reproducing means

55 and 54 respectively.

FIG. 9 shows transducer 54 and loudspeaker 55 connected in parallel driven by amplifier 56 activated by signal source 57. Transducer 54 and loudspeaker 55 have a

volume control

59 and 60 in their respective lines for controlling the volume of each independently of the other.

FIG. 10 shows transducer 54 and loudspeaker 55 driven by individual amplifiers 56. This allows for individual control for the transducer 54 and loudspeaker 55. Amplifiers 56 may be activated by the same signal or each amplifier 56 may be activated by a stereo signal source 58 such as a stereo phonograph record.

FIG. l1 shows loudspeaker 55 driven directly through leads 63 by amplifier 56 with amplifier 56 being activated by signal source 57 through leads 62. The input of amplifier 61 is connected to the output of amplifier 56 by leads 65 and the output of amplifier 61 is connected to transducer 54 by leads 64.

It should be understood that the transducer of the present invention requires more driving power to drive a large sounding board than is required to `drive a light loudspeaker paper cone. This is the reason means are shown in FIGS. 9, 10 and l1 to regulate the power to each

sound reproducing means

54 and 55. The sound from each reproducing means may be balanced to the exact loudness best suited to the individual listener.

Although several specific embodiments of this invention have been herein shown and described, it will be understood that details of the constructions shown may be altered or omitted without departing from the spirit of the invenion as defined by the following claims.

I claim:

1. An electro-mechanical transducer comprising a driving element including a magnetic core and a coil of wire Awound on said core, said core being solidly attached to a mounting plate, an armature of magnetizable material mounted in axially spaced relation with said magnetic core, resilient coupling means connecting said `armature element with said mounting plate for permitting relative motion and mutual power transfer in all directions between said driving element and said armature element, magnetic biasing means disposed generally parallel with said core between said mounting plate and said armture, a sounding board for supporting said transducer, and means rigidly connecting said armature to said sounding board.

2. An electro-mechanical transducer comprising a driving element including a magnetic core and a coil of wire wound on said core, said core being solidly attached to a mounting plate, an armature means of magnetizable material disposed in axially spaced relation with said magnetic core, resilient coupling means connecting said armature means with said mounting plate for permitting relative motion and mutual power transfer in all directions between said core and said armature means, and permanent magnet disposed generally parallel with said core between said mounting plate and said armature means.

3. A transducer element according to claim 1 or 2, wherein means is provided for mounting the armature on the sounding board in partial spaced relation therewith, whereby the armature may vibrate independently of the sounding board and its attachment thereto for imparting sound into the surrounding area.

4. An electro-mechanical transducer comprising a magnetic driving element and a magnetically driven element, means for resiliently coupling said driven element and said driving element in spaced relation with each other, a sounding board for supporting said transducer, and coupling means extending from the driven element for solidly attaching said driven element in spaced relation with and to a said sounding board, whereby said driven element may vibrate concurrently with and independently of said sounding board.

5. An electro-mechanical transducer for producing sound vibration comprising a magnetic core and an electrical coil wound on said core, said magnetic core being fixedly attached to a mounting plate, a magnetizable armature axially spaced from said magnetic core, spacing means extending generally parallel with said core between said mounting plate and said armature, and means for adjusting the axial spacing between said magnetic core and said armature, said adjusting means comprising axially slanting cam tracks located at the end of said spacing means opposite said armature, said mounting p-late having runners disposed to ride on said slanting cam tracks, and said mounting plate being rotatable on said tracks for moving said magnetic core axially toward and away from said aramture.

6. A transducer according to claim 5 wherein said spacin g means comprises a permanent magnet.

7. A transducer according to claim 5 or 6 wherein means are provided for holding said totatable mounting plate in a fixed position relative to the armature.

8. An electro-mechanical transducer according to claim 2 or 6 wherein the permanent magnet is a body having an opening extending therethrough from end to end, and said magnetic core extends into the opening of said body from the end thereof remote from .the armature.

9. With an electro-mechanical transducer according to any one of

claims

1, 2, 4, and 5 the combination of a dynamic speaker electrical coupled with said transducer to a signal source common to both the transducer and dynamic speaker.

References Cited UNITED STATES PATENTS 2,946,995 7/1960 Gosswiller 340-388 2,957,053 10/1960 Chichester 179-114 3,366,749 1/1968 Ries 179-1155 KATHLEEN H. CLAFFY, Primary Examiner.

ARTHUR A. MCGILL, Assistant Examiner.

US. Cl. X.R. 179-101