US2958740A - Electroacoustical transducer - Google Patents

Description

Nov. 1, 1960 R. E. KIRK 2,958,740

ELECTROACOUSTICAL TRANSDUCER Filed sept. 1, 1959 l zo lg ELEC'IROACOUSTICAL TRANSDUCER Roger E. Kirk, Waco, Tex., assignor to The Baldwin Piano Company, Cincinnati, Ohio, a corporation of Ohio Filed sept. V1, 1959, ser. No. 837,455

9 claims. (c1. 179-139) This invention relates generally to microphones, and more particularly to microphones which are especially adapted for communication purposes in locations with high background noise.

Voice communication in areas of high background noise experiences difliculty in both receiving and transmitting. Most of the difficulties in receiving in such high noise lareas are solved by means of headsets provided with sound shields which completely encompass the wearers ears. However, since vocal transmission generally involves sounds spoken from the mouth and the mouth and the nose are necessary for other bodily functions, the transmission of sound cannot simply be solved by the provision of a sound absorbent shield. If a microphone is mounted in a shield which covers the nose and mouth of the wearer as disclosed in the Patent No. 2,398,076 of Bulbuliam entitled Aviation Mask, communication is interrupted whenever the wearer desires to eat, smoke, or perform a number of other functions Which require removal of the mask. The mask is thus clearly inconvenient for the wearer and also tends to impair his vision. In addition, moisture as a result of breathing tends to attack the microphone and deleteriously affects its operation. If oxygen must be supplied to the wearer, as is often the case when the mask is employed in high altitude flying, the oxygen equipment increases the weight of the mask and requires compromises in the acoustical design of the mask. In addition, electrical failures may result in explosion of the oxygen.

It is, therefore, one of the objects of the present invention to provide a shielded microphone for communication in high background noise areas which need not be mounted in front of the mouth of the wearer but is capable of operating as a contact microphone on some other part of the body.

The contact microphones which have been known, such as that disclosed in Patentl No. 2,121,779 entitled Sound Translating Apparatus to Ballantine, have not proven satisfactory even for use in areas of low background noise because of their inability to faithfully reproduce vocal sounds. It is therefore a further object of the present invention toprovide a contact type microphone capable of more faithful reproduction of vocal sounds than those contact microphones which have existed heretofore.

It is also an object of the present invention to provide a communication type microphone capable ofr responding to speech within an area of high background noise which produces an improved signal-to background noise ratio.

The objects of this invention are achieved by providing a pressure gradient acoustical transducer mounted within a cavity in a sound or acoustical shield. Pressure gradient acoustical transducers are also known to the art, as disclosed in Patent No. 2,587,684 entitled Directional Microphone to B. Bauer, and produce a response equal to` the pressure differences on two sound tetes att` 2,958,746 Patented Nov. 1, 1960 sensitive surfaces, generally the front and back surfaces of the acoustical transducer diaphragm. A microphone constructed according to the present invention equally attenuates the -background noises at the two sound sensitive surfaces of the transducer, however, only one of the sound sensitive surfaces is shielded from the confronting surface of the microphone wearer so that the microphone becomes responsive to the sound pressure exerted on the other surface of the acoustical transducer.

The invention and its utilities will be more fully appreciated from the following description of a preferred embodiment of the invention which is illustrated in the figures, in which: Y

lFigure l is a diagrammatic view of. a microphone embodying the principles of the present invention, the View being taken in vertical section;

Figure 2 is a lower plan View of a microphone which constitutes a preferred embodiment of the present invention;

Figure 3 is a sectional view of the microphone of Figure 2 taken along the line 3-3 of Figure 2;`

Figure 4 is a sectional view of the microphone of Figures 2 and 3 taken along the line 4--4 of Figure 2; and

Figure 5 is a top plan view of the microphone illustrated in Figures 2, 3, and 4.

Figure l illustrates a pressure gradient electroacoust-ical transducer 11i mounted within -a cavity 12 of a microphone casing 14. The casing 14 is of sound attenuating material and may be compliant as in the case of rubber or soft plastic, or may be a rigid body such as clay or hard plastic. The casing 14 is in contact with the skin or surface of a person using the microphone, designated 16. This surface may be the throat of the person, the cheek, the forehead, the temples or some other part of the anatomy.

The electroacoustical transducer 11i has opposite surfaces 18 and 21B which are sound sensitive, and these surfaces are disposed normal to the surface of the skin 16 of the person using the microphone. This is a preferable construction because each of the surfaces 18 and 20 will experience sound pressures from ambient noise which have been approximately equally attenuated by the casing 14, however, it is possible to obtain equal sound attenuation for ambient noises with the surfaces 18 and 20 disposed at different angles to the surface of the skin 16. The sound responsive surface 21) is in communication with the skin 16 through a passage 22, however, the sound responsive surface 18 is shielded from the skin 16 by the casing 14. A small chamber 24 confronts the sound responsive surface 18 in order to approach the same acoustical loading on the surface 18 as provided by the passage 22 for the surface 20 of the electroacoustical transducer 11i. Straps 25 are secured to opposite sides of the casing 14 to secure the microphone to the body of the user.

Ambient noises will strike both the sound sensitive surfaces 18 -and 21) of the electroacoustical transducer 10 with approximately equal pressures, and since the electroacoustical transducer 1.0v responds to differences in the sound pressures on the two surfaces, the responses of the two surfaces to ambient noises essentially cancel each other. Sounds produced by the skin 16 are transmitted through the passage 22 and impressed upon the sound sensitive surface 2@ of the transducer 10, and since the sound sensitive surface 18 is shielded from the skin 16, the transducer responds directly to these sounds.

The constructional details of a microphone of preferred construction which operates on the principle described with reference to Figure l is shown in Figures 2 through 5; ln these figures, the microphone is illustrated with a casing 26 having an essentially semi-spherical outer surface 28 which extends from a central circular bore 30. A cone shaped recess 32 extends into the casing symmetrically about the axis of the bore 30 and from the opposite side of the casing. A flat wall 34 extends centrally across the recess 32, and the wall 34 is provided with a cylindrical projection 36 which is snugly anchored within the bore 30 of the casing 26. The wall 34 divides the recess 32 into two chambers 38 and 40, and a cylindrical channel or opening 42 extends through the wall 34 between the two chambers 38 and 40, the opening 42 being disposed on the axis of the bore 30 in the casing 26. A cylindrical electroacousticaltransducer 44 is snugly mounted within the opening 42 in the wall 34,.and the sound sensitive surfaces of the pressure gradient transducer 44 are designated 46 and i8 and confront the two chambers 38 and 40, respectively.

As indicated in Figure 3, the sound sensitive surface 46 is formed by a diaphragm 50, and the sound sensitive surface 48 is formed by a diaphragm 52. The diaphragms 50 and 52 are interconnected at their centers by a coupling rod 54, and the peripheries of the diaphragms abut coaxially mounted, hollow cylindrical magnets S6 and S8. A magnetic sleeve 60 is disposed about the rod 54 and is mounted to the magnets 56 and 58 by a disc shaped ange 62 extending normally from the rod and disposed between the magnets 56 and 58. The sleeve 60 confronts and is spaced from each of the magnetic diaphragms and 52, thereby forming two magnetic gaps, and the sleeve 65B supports serially connected coils 64 and 66 wound about the sleeve 60 on opposite sides of the flange 62. This electroacoustical transducer is more thoroughly described in the patent of Robert K. Duncan, No. 2,950,358 entitled Electromechanical Transducer.

A plate 68 of sound absorbent material is mounted to the end of the wall 34 opposite the casing 26 and extends across the chamber 4t) to the peripheral edge of the casing 26. The plate 68 carries a layer 76 of material simulating the acoustical properties of body tissue on its surface confronting the chamber 40.

A at, hollow, circular tube 72 is mounted to the casing 26 and plate 68 to provide a suitable contact and seal with the body tissue of the person wearing the microphone. The tube 72 has a channel 74 extending therethrough which is lled with a liquid 76 to form a cushion between the microphone and the body tissue. Straps 78 are attached to opposite sides of the casing 26 for the purpose of securing the microphone in contact with the skin of the person employing the microphone.

When the tube 72 is disposed in contact with the body tissue of a portion of the body carrying speech energy, the speech energy enters into the recess 32, but due to the plate 68, the speech energy is substantially shielded from the chamber 40 while the speech energy freely enters the chamber 38. Since the chambers 38 and 40 are shaped to form horns with the diaphragm 50 and the diaphragm 52 essentially at the throats of the ho-rns, optimum transmission of speech energy is achieved through the chamber 35, and optimum acoustical coupling to the diaphragm 50 is also achieved. The chambefr 40 is made as near identical to the chamber 38 as possible so that ambient noises passing thorugh the casing 26 are impressed upon the diahpragm 52 in approximately the same amplitude as they are impressed upon the diaphragm 50 Iconfronting the chamber 38. It is preferable that the portion o-f the chamber confronting the body tissue for both chambers 38 and 40 be identical, and for this reason the layer 70 which closes the end of the chamber 4t) opposite the casing 26 is constructed of material having approximately the same properties as body tissue or skin. It has been found that neoprene of the proper durometer achieves this end,

and therefore the layer 70 in a preferred construction of the microphone described herein is a 1/16 inch sheet of neoprene. The plate 68must function to attenuate sound, however, it must alsofoccupy a minimum of space in order to permit the chamber `4t! to resemble the chamber 38 as near as possible. For this reason, an aluminum sheet is employed for the plate 68, although other materials such as brass could also be employe-d.

The wall 314 is also constructed of neoprene and is 1/2 inch thick. The purpose of using neoprene for the wall 34 is to provide a cushion mounting for the elec-troacoustical transducer 44. The casing 26 is constructed of clay, and hence is a rigid body. However, the casing could also be constructed of a compliant material, such as polyethylene plastic or rubber. The functions of the casing are to support the electroacoustical transducer 44 and to attenuate impinging sound from the ambient atmosphere. The tube 72 is constructed of polyethylene plastic, and theV liquid 76 is glycerine. Since the plastic of the tube 72 is compliant, exerting of a pressure on one portion of the tube .results in redistribution of the liquid therein.

It is to be noted that the pressure gradient electroacoustical transducer 44 is of a type which employs two spaced diaphragms. It is to be understood that the invention is not limited to this type of electroacoustical transducer, and that the electroacoustical transducer may be any type of pressure gradient transducer. It is to be noted that the transducer functions as a pressure gradient transducer for background noises and essentially as a pressure transducer for sounds striking the diaphragm in communication with the body tissue as a result of the casing construction.

From the foregoing -disclosure it will be apparent to those skilled in the art that microphones may be constructed in many different configurations other than that disclosed while utilizing the teachings of the present invention. It is therefore intended that the scope of the present invention be not limited by the foregoing disclosure, but rather only by the appended claims.

The invention claimed is:

1. A microphone suitable for use with high background noise having a sound attenuating casing, and an electroacoustical transducer mounted within the casing, said transducer having two sound responsive surfaces, and being responsive to the sound pressure difference between the two surfaces, characterized by the construction wherein the casing is provided with a sound passage from the exterior thereof to one of the sound responsive surfaces of the transducer, and is provided with a sound absorbent layer between the other sound responsive surface of the transducer and all portions off the exterior surface of the casing. y

2. A microphone suitable for use with high background noise having a sound attenuating hollow casing and an electroacoustical transducer mounted within the casing, said transducer having two parallel sound responsive surfaces and being responsive to the difference in sound pressure on the two surfaces characterized by the construction wherein the casing is provided with a wall dividing the casing interior into two chambersand hav- `ing an opening therein, the transducer being acoustically sealed within the opening with one sound sensitive surface confronting each chamber, and said casing having a sound passage extending from one of the chambers tothe exterior thereof and enclosing the other chamber.

3. A microphone suitable for use with high background noise ycomprising a body of sound attenuating material having a recess on one side thereof extending therein from a mouth, an electroacoustic transducer having two sound responsive surfaces and being responsive to the difference in sound pressures impinging on the two surfaces, said transducer being mounted in the recess of thebody with both surfaces substantially equally shielded from sounds entering the recess through the body, and

means disposed between only one of the surfaces and the mouth of the recess for acoustically shielding said su-rface rom sounds entering through the mouth of the recess.

4. A microphone suitable Ifor use with high backgnound noise comprising a body of sound attenuating material having a recess on one side thereof extending therein from a mouth, a wall mounted tol the body extending across Ithe recess and dividing the recess into two essentially equal portions, said wall having an opening therein, an electromechanical transducer acoustically sealed within the opening in the wall having a diaphragm confronting each of the two portions of the recess, said transducer being responsive to the sound pressure difference exerted thereon from the two portions of the recess, and a sound attenuating member extending from the wall to the body across only one of the two port-ions of the recess, said member acoustically shielding the one portion of the recess from sound entering therein from the mouth of the recess.

5. A microphone `comprising the elements of claim 4 wherein the recess in the body is conical, whereby each portion of the recess forms a horn to :loa-d the confronting diaphragm.

6. A microphone comprising the elements of claim 4 wherein the sound attenuating member is provided with a surface confronting the one portion of the recess having the acoustical properties of human skin.

7. A microphone comprising the elements of claim 4 wherein the sound attenuating member is provided with a layer of neoprene confronting the one portion of the recess.

8. A microphone suitable for use with high background noise comprising the elements of claim 3 in combination with an endless hollow tube sealed and mounted to the casing about the month thereof, said tube being constructed of compliant material and having a liquid on the interior thereof.

9. A contact type microphone suitable for use with high background noise comprising, in combination, a semispherical solid body of sound attenuating material having a radial bore extending therethrough at its center and a conical recess extending therein from the side opposite the spherical surface coaxially with the bore, a neoprene wall mounted within the recess onI the axis thereof dividing the recess -into two equal port-ions, said wall having a cylindrical projection sealed within the bore of the casing and an opening extending therethrough transversely intersecting the axis of the bore of the casing, an electromechanical transducer acoustically sealed within the opening having a pair of diaphragms confronting the two portions of the recess, said transducer being electrically responsive to the diierence in sound pressure on the two diaphragme a plate sealed to lthe end of the wall opposite the casing and to the portion of the casing adjacent to the `one portion of the recess on one side of the wall, a layer of neoprene disposed on the plate confronting the one portion of the recess, and a circular hollow liquid lled tube of compliant material sealed to the casing about the recess.

No references cited.

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