US 2350010 A
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M y 1944- I F. c. BEEYKLEY 2,350,010
MICROPHONE Filed Dec. 26, 1941 GACKGEOUNO Patented May 30,1944- MICROPHONE Francis Cheyney Beekley, West Hartford, Conn., assignor to .The Glastonbury Bank a Trust Company, Glastonbury, Conm, a banking corporation of Connecticut. as trustee Application December 26, 1941, Serial No. 424,43?
This invention relates to means responsive to sound for creating electricv pulses, such as a microphone adaptable for use in radio broadcasting, radio and wire-telephone, communications, signaling, or public address systems.
' In electricalltransmission of sound, it is desirable to eliminate background noises to assure clarity and'substantially perfect transmission or the speech, music, or other sounds which constitute the material intended to be transmitted. This is accomplished in radio broadcasting, for instance, by locating microphone and performer in a soundproof studio. 'l'here are, however, many cases where it is impracticable to locate a microphone in an enclosure properly soundproofed against extemalnoises and intemal reverberation. Examples of thi include radio broadcasting of sports events and conventions and political gatherings, public address systems, military and other communications. where transmission must be made from noisy locations or reverberatory enclosures.
I cancellation of the background noises and the nai The primary object of this invention is to pro-' vide a microphone which may be used in a noisy or reverberatory. location. which microphone will automatically cancel out all or a material portion of the backgroundnoise and thereby permit transmission of speech or other desire sounds having acceptable fidelity.
A further obiectis to provide a microphone with vibrating means so arranged therein as to illustrating a .diflerent electrical connection be-f I tween two sound-responsive units of the carbon granule type;
Fig. 4 is a diagrammatic view or a device the ing two sound-responsive units of the. magnetic type: v
Fig. 5 is a diagrammatic view illustrating the ture of the excitation waves of the microphone;
Fig. 6 is a cross sectional view of still another embodiment of the invention;
Fig. 7 is a perspective view of one form which the Fig. 6 embodiment may take; and
Fig. 8 is of Fig. '7.
Referring to the drawing, and particularly to Figs. 1 to 5, inclusive, which illustrate one em.- bodiment of the invention, the numeral ill designates a base plate having an elongated form bent centrally at II to provide two angularly disposed end portions l2. 'ljhese end portions are preferably oi a size and shape to have mounted thereon two casing portions whose axes exten perpendicular to the plane of the face of the plate Portion I2 upon which each is mounted. The
- faces I of the casing portions "have openings therein and are disposed in the same angular-replation that the plate portions I! bear to each be adapted to receive background noisesi'rom all:
directions in counterbalancing or cancelling relations. applied thereto intentionally in an unbalanced relation.
tion: such microphone actuable only by. vibra- A further object is to provide a microphone which is substantially unafl'ected by noises originating from any point at a distance and adapted to be excited only by vibrations originating close by and in properly directed relation.
A further obiectis to provide .a microphone 'with diaphragm means subject to e'xcitation in counterbalancing or cancelling relation, by vibrations originating at a distance therefrom and in any angular relation to.
Other objects will be apparent from the drawing and appended claims.
Fig. 1 is a side elevation of'one embodiment of the invention:
. Fig. 2 is a diagrammatic view oi an embodiment of the invention utilizing two sound-responsivli uiinitsoithecarbougranuletypep 21 which may 3 is a diagrammatic view of the invention 58 other, namely, in obtuse angled relation. An electrical conductor I5 projects from the base ll 1 and is connected with the microphone.
'I'he'mlcrophone further includes vibrating 'means including difierent sound-receiving portions spaced in close relationship, such as the diaphralgms. It and I1 (see Flg. 12) each of which may be located within one or the casings I 4. Associated with each diaphragm is an electrical means 1 including a button or housing I. separated there 7 a sectional'view taken on line 8-1 from by a felt washer l9; said housing being filled with a plurality oi loosel arranged small carbon granules 20. Diaphragm II is electrically connected by conductor 2!, in which may be interposed a battery 22, with one end of the primary coil 23 01 a transformer. The opposite end of said coil is connectedby conductor-'24 with the button associated with diaphragm I. A com .ductor 25 connects the button I l associated with diaphragm ll with a second primary transformer coil 2 at the end of is connected. The
pposlteendof coil flisconnected with di phragm ll by mean of conductor have battery 28 interposed there'- in. The coils II and it constitute separate primary coils of a suitable transformer having cores the coil li'complementaryj to the end of coil 23. with which conductor 2! 29 and 30 associated with coils 23 and 2t resmctively, and having a single secondary coil ti associated with both cores. The two diaphragm units are connected to the transformer primaries in opposite or counterbalanc'ing relation.
Referring to the Fig. 3 construction, two diaphragm units, each housed in a casing portion 53, are connected in counterbalancing electric relationship. 'lhus, diaphragm 32 is connected by conductor 33, including a battery it, with the j primary coil 35 of one transformer. The other end of coil 35 is connected.by conductor 3% with the button 3i associated with diaphragm 32. lihe other diaphragm 38 is connected by conductor 39, which has battery 5i interposed therein, with. one end of primary transformer coil it. ll'he other end of coil it is connected by conductor M with the button 62 associated with diaphragm 38. The transformer of which the coil 35 con stitutes the primary has a core 33 and a secondary coil M. The transformer of which the coil til constitutes the primary has a core tdand a secondary coil tit. A conductor i'l connects adjacent ends of the transformer secondary coils at and t6, and a line dt-connects the opposite ends of transformer secondary coils dd and it. Lead line 49 is connected with line at and lead line 50 is connected with conductor at.
In the embodiment illustrated in Fig. a, dia phragm has a coil 55 connected therewith. A permanent magnet 51 is associated with diaphragm 55 and carries two pole pieces 55 adjacent its ends and each extending adjacent opposite sides of coil 56. Another pole piece 5%! is carried centrally by magnet 51 and extends within coil 56. The two units employed in the Fig. embodimentare of similar construction, and like parts bear the same reference numerals. A conductor 5i connects one end of one coil 56 with the opposite end of the other coil 56, and a conductor 62 connects other ends of the two coils 56. Leads G3extend from conductors 6i and 52.
Each of the Figs. 2, 3, and 4 embodiments is operable for the intended purpose of cancelling out background noises and transmits only properly directed vibrations emitted in close spaced relation to one diaphragm or membrane when the two following requirements are met. These two requirements are: first, that the diaphragms placed substantially 180" so that they will fully counterbalance each other. Whenthese two requirements are satisfied in any of the aforementioned embodiments, the output of each unit will be that represented diagrammatically in Fig. 5, wherein the output from one unitin reference to background noises will be represented by one of the dotted wave lines, while the output of the other will be represented by the'other dotted wave line. Note that these wave lines are in counterbalancing relation and hence will cancel out and eliminate background or ambient noises. The full line in Fig. 5 represents the signal wave produced by the one unit against which vibrations are directed from a close spaced emission point. As used herein, the, term- "ambient". when referring to sounds or noises will be understood to mean unwanted surrounding sounds or noises, i. e. external sounds or noises not desired to be transmitted.
assume in the use or the microphones described above, it is essential that thevibrations constituting the signal to be transmitted shall be emitted at a point spaced close to and directed toward one only of the membranes or diaphragms, so as to reduce to a minimum the efieco oi the signai upon the other diaphragm. This avoids the cancelling effect which actuation or" the other diaphragrn will have on the intended signaling vi oration. In this connection, tests of units eznbodying theaters-said invention, and particu larly the d embodiment, show that, whereas signals tr itted from a conventional micron a military tank while that tanl: e have a poor percentage of the use of a microphone embodying ions with respect to volume and character of bacliground'noise produce a greatly in= creased degree of intelligibiiity. Fence, a neicro phone constructed according to "event-ion overcomes very serious obstacles heretofore en countered in radio transmission, especially for military communications, and raises the percentage of intelligibility over adverse conditions to an extent which reduces materiaily the possibility that signals will be misunderstood or undecipherable at the receiver. While twoseparate casing portions have been shown and described,
' it will be understood that this is illustrative only,
- which is so arranged that it is balanced with intermediate the pole pieces 12.
relation to both of the openings ti and as and divides housing 65 into two chambers or sub stantially the same size and shape. Therefore, if vibrations or sound waves are applied equally at the housing openings EL-td, they will act equally and oppositely upon the diaphragm iii to prevent vibration thereof. A magnet "H hat/- mg pole pieces '32 is carried by housingttat one side of diaphragm l0, and a pole piece it is carried centrally of magnet Ii and positioned A coil Hi is connected to the diaphragm in a well known manner. It will be observed that when the sound waves constituting a signal are emitted in close spaced relation to and are directed into one oi the openings 61-68, the diaphragm it wi l be caused tovibrate, and hence to actuate the elec tromagnet portion of the microphone to trans unit the intended signal.
The embodiment illustrated in Figs. 7 and it, a variant of the embodiment illustrated in 6, has been found efllclent in operation. In this embodiment, cylindrical housing d9 having plane parallel end members at has diaphragm or vi brating member 82 mounted centrally between and parallel to the end walls 8|.
A button 83 confines carbon granules and leads 8t and lit extend from the diaphragm t2 and the button 83. The cylindrical body portion of the housing 83 has a pair of openings 8? formed therein. These openings are preferably elongated'and equally spaced to either side of the diaphragm 82, whereby the opposed surfaces of the diaphragm constitute spaced sound-receiving portions. These openings 81 are spaced apart circumferentially a small distance, preferably not greatly in excess of inch and hence only a small fraction, i. e., not exceeding one fourth, of a wave length of sound of the highest frequency which it is desirable to cancel. It will be observed that sound waves entering these two openings 81 will act equally and oppositely upon the diaphragm 82. whereas sound waves applied in close spaced relation to one only of the openings Bl as indicated by the arrow in Fig. 3 will vibrate the diaphragm 82 to actuate the microphone. In practice, such application of a spoken signal intended for transmission is accomplished by speaking directly into one only of openings 81 while the microphone is held in close spaced relation to or even in contact with the lips of the user.
It will be observed that each of these embodiments of the invention employs the principle of automatically counterbalancing within the microphone sound waves impressed in balance at two spaced portions of the microphone. This counterbalancing cancels any unwanted signal or vibration which normally would excite a microphone positioned in a noisy location. These two portions may constitute either the two .diaphragms in the embodiment of Figs. 1 to 4 or the opposite faces of a single diaphragm in the embodiment of Figs. 6 to 8. At the same time, an announcer may speak into .the microphone or cause selected signals to be emitted in a selected direction and at close spaced relation to the microphone for the purpose of causing its operation to transmit the desired signal substantially without interference from background noises. The effect is produced when the device is properly constructed, and the only care required is to insure proper direction and emission of the sound waves which are to constitute the intended signal so that there will be' a difference in either amplitude or phase of the sound re oeived at the two portions of the microphone aforementioned.
I claim as my invention:
waves to said directing means for unbalanced impression thereof on said vibrating means.
4. A microphone comprising diaphragm means, means spaced apart approximately three eighths of an inch for normally directing ambient sound waves for impression upon two surfaces of said vibrating means substantially in phase, and electrical means adapted to be energized by said diaphragm means, said electrical means transmitting a signal in response to sound waves-impressed on said diaphragm surfaces in unbalanced relation only.
5. In a microphone, vibrating means, electrical means responsive to said vibrating means for transmitting a signal, and means arranged to permit ambient sound waves to impinge upon said vibrating means at spaced points substantially in phase and in substantially equal amplitude so that they oppose and substantially cancel out their combined eflect.
6. A microphone comprising vibrating means, means for housing said vibrating means, said housing means having a pair of openings in com- 1. A microphone comprising vibration means having two non-directional sound-receiving portions, spaced apart a small fraction ofa wave length of audible sound for normally equal impression of sound thereon, and electrical signal means responsive to said vibration means, said electrical means being rendered operative to transmit a signal only when sound is impressed I derantly'against one of said points.
3. In a microphone, vibrating means, means spaced apart not more than one fourth wave length for directing sound waves originating at a distance for impression upon said vibrating means in substantially identical phase and amplitude, and electrical means responsive to said vibrating means and actuable to transmit a sig-- nal only upon unbalanced application of sound plementary relation to said vibrating means for passage of sound waves to impress said waves on said vibrating means at spaced points in substantially identical phase and amplitude, and electrical means responsive to said vibrating means for transmitting a signal only when sound waves are emitted in close spaced relation to and directed at one opening.
'7. A microphone comprisin vibrating means having two sound-responsive surfaces, electrical means associated with said vibrating means, and means spaced apart less than one inch for directing sound waves originating at a distance from said microphone and from any or all directions to impress said waves upon said two sound-responsive surfaces in substantially identical phase and amplitude, said electrical means being actuable to transmit a signal only when sound waves are unequally applied to said two sound-responsive surfaces.
8. A microphone having a casing, and a diaphragm in said casing, said casing having a pair of openings in complementary relation to said diaphragm for exposing the opposite faces of said diaphragm to equal counterbalancing impact by ambient sounds originating at a distance from said microphone.
9. A microphone comprising housing means including two complementary independent chambers each having an opening, vibrating means having spaced portions each exposed at one chamber, and electrical means responsive to said vibrating means, said openings being close spaced and arranged in complementary relation to said vibrating portions, said electrical means being actuable to transmit a signal only upon unbalanced reception of sound in said chambers.
10. A microphone comprising a pair of diaphragms having substantially equal characteristics of vibration, means fixedly mounting said diaphragms in juxtaposed relation, and electrical means energized by each diaphragm, said electrical means having a counterbalancing phase relation.
11. A microphone comprising a pair of matching non-directional diaphragms, a mounting securing said diaphragms in fixed relation spaced 9. small fraction of a wave length of audible sound, and electrical means responsive to each diaphragm, the phase angles of said electrical means being displaced.
12. lA microphone comprising a pair of nonwaves substantially in phase and equal amplitude, the electrical means of sai units being ;connected-180 out of phase.
13. A microphone including a pair of vibrating membranes, said membranes havin matching vibration characteristics, and means for counterbalancing equal components of vibration impressed simultaneously on both membranes.
14. A microphone comprising a housing having a pair of similar openings spaced apart less than one-fourth of a wave length of sound of the highest frequency of any selected portion of the audio frequency range, a vibrating membrane mounted in said housing in complementary relation to and between said openings, and electrical means associated with and responsive to vibrations of said membrane.
15. A microphone comprising a housing having a pair of similar openings spaced approximately three-eighths of an inch, a vibrating membrane mounted in said housing in complementary relation to and between said openings, and electrical means associated with and responsive to vibrations of said membrane.
16. A microphone comprising a housing, a vibrating membrane mounted substantially centrally in said housing, and electrical means associated with and responsive to vibrations of said membrane, said housing having a pair of close spaced divergently facing similar openings therein on opposite sides of and in complementary relation to said membrane.
FRANCIS CHEYNEY BEEKLEY.