Патент USA US2121781код для вставки
June 28, 1938. .,s. BALLANTINE 2,121,781 SOUND TRANSLATING DEVICE` Filed April 1:5, 19:56 .Y 2 Sheets-Sheet l »w¿1%. .. June 28, 1938. A 2,121,781 s. BALLANTINE soUND TRANSLATING DEVICE Filed April l5, 1936 2 Sheets-Sheet 2 COW1 QOCQOM-.D,E «xuSì.EmiNwSl I ll’altenfed'Ju?e I. ` y' Y i. _ l ',.UNlTi-:D-„sTATi-:s PATENTor-'FICE A I - com raïszïgna A " ' „ÍÍÄÉ‘ÄÍÜZÍÈÈÉÍÈÈÍÜÄM 9 (ci. 11a-114) This inventionerelates to apparatus for translating mechanical vibrations of the body in the Fig. 12 is a vlongitudinal section through a transducer which includes a _diñerent form of vi-v ' region of the throat due to the voice into articu»l y bratory armature; and late speechy sounds or into electrical currents. Fig. ,13 is a fragmentary circuit diagram of a 5 which yield articulate speech sounds when reproduced. > , A - complete electrical system which embodies the 5 ~invention. , Apparatus and methods for this general puri ' 'I'he microphone is adapted to be> worn around ' posehavebeen described in my copending appli-~- the neck like a collar, as shown in Fig. 1 of my cations Ser. Nos. 6,245 and 6,246, filed Feb. 12, v 10 1935; Ser. No. 8,392. flied Feb. 26, 1935, and Ser. No. 54,347,1l1ed December 13, 1935. l » i copending application Ser. No. 6,246, but other methods of support may be employed. When 10 . worn as a collar, the .microphone M has the gen- « i A l -An object of the invention is to provide a device eral fOrm 0f a narrow band 0r casing in which of novel construction for converting acoustical two mediano-electrical transducers are symmet vibrations of the body due to the voice into elec- rically arranged, and an adjustable elastic band . ' 15 tric currents for transmission in an electrical B is sewed to the casing toV form a collar that may 1s ' communication'system. An object is to provide'A be placed around theV neck in such a way that . a microphone, of the character stated, ‘ which operates on the electromagnetic principleand _ which therefore does not requirethe battery or- 20 dinarily used with microphones of the carbon ’ granule type, ' - . ~ - lFurther objects are to provide a larynx micro- phone which is characterized by 'a >simple and rugged mechanical construction and by an elecl the microphone units are in contact with the neck in the region of the larynx. ` , ' The. covering or elongated casing I for the ` transducer unit or units may be of any suitable 20 material, such as-glove leather, with a snap fas tener 2 and fibre stiffener 3 fastened to one end ' - ` of the casing. The side of the microphone whichcontacts with the neck 'will be designated, for 25 't1-ical oui-,put which compensates, in part atleast, ^ convenience of description., as the “front” of the 25 for the deficiency of the higher frequency constituents in the mechanical vibrations or the larynx. _ ~ These and other objects and advantages of the invention will be vapparent from the -following 30 specincation whentaken with the accompanying ' drawings in which: , Y” > microphone. >The front wall of the casing I is provided with two holes which are covered by a thin membranous material l _which may be ce mented to the front leather wall, and the actu-` 1 ating buttons 5 of the microphone units extend 3o through these holes. 'Not all materials are suit Fig. 1 is a sectional view of an embodiment of ' able for the membrane I on account of attenu- f the invention; ‘ `_ ation of the higher frequency vibrations. Ma Figs. 2 and 3 are front and rear views, respec- ' terials which have been used successfully are thin 35 tively, with parts broken’away, of one of the transducer units; ` Y ' ` rubber, animal intestinal linings which may be -35 grouped under the name of “colon leather”, and Y Fig.` 4 is a schematic view of the wiring con- f- ordinary leather of the >order 'ci .005" to .015" nections and shielding of the microphone shown thickness. ‘ Thinglove leather has been employed in Fig. 1; ¿ ' 40 « - - f in most of my constructions becauseof its good Figs. 5a and 5b are corresponding mechanical and electrical impedance diagrams; Fig. 6 is a curve sheet showing typical output voltage-frequency characteristics which may be obtainedvwith embodiments of the invention; _ 45 Fig.7 isa front view of another transducer con- mechanical qualities and because its physical ap-` 40 struction which is particularly- adapted for oil pearance can be made to match the rest of the leather covering. This is cemented to the cov ering I with rubber cement and extends over Vthe entire area of the side toward the'neck. In order to reduce the strain on the .covering I and the `4,5 .` thin protective- covering 4', a thin metal grommet damping; » '8 is sewed and/or cemented around the edge of _ _ f I‘T'ig. 8.is a longitudinal section on line 8_8 of . the openings in the front wall I. "Fig 7; A 5o ' ' l Fig. 9 is a central transverse sectioni ï The electromagnetic transducer units may be, . . . Fig. 10 is a longitudinal section -through ' and V,preferably are, _fof substantially identical 50 ' construction.A The motion transmitting button transducer which includes adjustableY elements 5 is of substantiallyrigid material, such as “bake- for controlling the air gap; lite”, balsa wood,vwhite pine, etc., andis fastened _v ` ~ i ' Hg.11isasectionalviewofatransducerwhich. Vtothe middle of the vibratoty element‘l. ,This , ‘ 55 includes another form'of magnet structure; _ vibratory element is- a resilient strip ,of` mag-55 ' _ l 2 2,121,7s1 netic material, such as silicon steel, which may have metallic pieces 8, 8' soldered at the ends thereof to assist in deñning the eifective length l ' c ` by varying this dimension the impedance of the transducer can be regulated inrelation to that of the larynx with which it is in contact. lWith of the vibratory strip or amature, thus render ing the resonant frequency substantially inde a length and thickness as given above', widths of from 0.2 to 0.7 inch are suitable for the aver age larynx. pendent of the vicissitudes of` assembly, screw pressure, etc. The end pieces are not essential but, when used, are usually somewhat thicker than the vibratory strip and partake of its vi 10 brations only to a minor extent. The magnetic strip'1 bridges across the ends of a ñat E-shaped magnetic yoke that, as shown in Figs. 1 and 2, comprises end pole pieces 9, 9' on a backing strip I0 which carries a central and somewhat shorter 15 pole piece I0'. The pole pieces 9, 9’ are perma nent magnets of suitable material such as co balt steel, aluminum-iron steel or the like which 1 ` l The air gap may be> adjusted by screws I8 which pass through the resilient strip 1 and into the back piece I0, but such an adjustment » oi the air gap adects the resonant period of the 10 armature and this effect must be taken into consideration in the design. Other methods of adjusting the air gap will be described later. Flexible conductors Id, , I4' of tinsel or the like are soldered to the pins I2 and are relieved 15 from strains by fabric tabs Il“ which are woven -into thecords and tied to eyelets 'II". The cords are magnetized, as indicated by the polar desig- v pass through shielding springs I5 that are sol dered to the clamps I8 and thus grounded on nations, N, S, to present like polesto the vibra the unit. The springs are of phosphor bronze, 20 tory armature. The back piece or strip I0 is of 20 ,iron having a lowvariational reluctance, such as Y steel or other material which will stand repeated bendings. `The unit itself is protected from ex ternal ñelds by a close ñtting metallic c_asing I1 which has `a `slightly domed bottom wall to pro vide space for the terminal connections and the 25 ends of springs I5. The connecting cords branch from the main cable at the middle of the mi pure annealed or Swedish iron. A small air gap of the order of from 0.001 to 0.010 inch is pro-> vided between the pole piece I0' and the vibra 25 tory strip 1, and a multi-turn coil of _insulated wire Il surrounds this pole and has its leads brought out through terminal pins I2 that pass through insulating bushings I2' which are held crophone strap, see Fig. 4, the shielding lead or braided conductor I8 being connected to the neg in the back piece I0 of `the magnetic yoke The vibrations. of the throat are picked up by ,ative terminal pin I2 of one unit and to the shield 30 30 the button 5 and communicated to the amature springs I5 of both units by a T-shaped metallic 1 and, due to the mass of the transducer unit « piece I9 that fits around the bifurcation of the which prevents it from vibrating as a Whole, the cable and prevents relative movement loi the forces imparted to the armature 1 result in a cable and the branch connections. The central vibration of the amature with respectto the conductor 20 of the cable is .connected to the 35 magnetic ñeld system. The air gap is therefore positive terminal of the other unit by one lead Y I4, and the unlike terminals of the two units t periodically altered in conformity with the vi are’ connected by lead I4’. The braided lead IB brations and the variations influx through the central pole I0' inducevan electromotive force ' preferably has an outer covering I8' - of soft in the'coil Ii which may be led to the. external rubber and the entire cable is, of course, quite 40 electrical circuits, ampliiiers, line, etc. Due to _iiexible. -The described connections place the the polarity of the permanent magnets, their. two units lin series, and this has given good re flux adds up in the central pole and the two ìs‘ìults erin practice but other connections could e us . l halves of the symmetrical magnetic circuit may The transducer units may be protected against v be regardedas in parallel. . Y 45 The thickness of the- resilient strip 1, and its the weather and sea spray when used in open length between the edges of the end pieces 8, 8', cockpit airplanes and seaplanes by placing the _ ~ are so chosen that the armature is mechanically ' units in closely ñtting bags of thin rubber hav resonant> at the upper end of the range of speech Y in_g a thickness of the order of 0.002 to 0.005 inch. ` v frequencies to be reproduced.V Good results have u The open ends of the bags are cemented together 50 beenv obtained by making the _ armature reso vnant at frequencies above'1000 cycles and, in most’of my constructions, they have been reso nant between 2500 and l4000 cycles. The natural frequency of vibration of an elastic slab clamped Y at its ends varies as t/l2, where t is the .thickness and Zvthe'length, and is' independent of the width and to the rubber covering I8' of the cable by rubber cement. The transducer _units are then sewed into the leather covering of the microphone strap. The microphone and its associated electrical 55, circuits are designed and/or adjusted to have overall frequency characteristics such as de to the first order. However, no rigorous rule can scribed in my copending applications Ser. Nos. ,i be given for _the calculation of the resonant fre v 6,246 and 54,347. >A mechanical impedance dla' 60 quency on account ofA thepresence of the buttonv ,5 which‘tends to lower the frequency by adding mass and to increase it by virtue of the added resistance `to bending caused by the' cementing vof the lower planar surface of the button to the ~ 05 armature. ' The above rule does furnisha _good practical guide, however, andthe exact‘diinen-` sions can be determined experimentally.- Typical dimensions which I‘have employed with lsilicon 1 steel for a resonant_'frequency in the neighbor hood of 3500 cycles are l==0.8 inch, t=0.014 inch, , I andwidth varying from 0.25 to 0.6 inch. Al though the resonant frequency is not greatly affected by variations in the width of the arma. »ture, theV width does „affect the mechanical im pedance as Vviewed from the'button 5 «so that gram of the microphone is shown in Fig. 5a, and l60 an approximate electrical circuit lequivalent of the mechanical system is shown in Fig. 5b. -In these diagrams, vo represents the impressed veloc ity due to the vibrations of the larynx, Zu repre sents the mechanical impedance of the throat 65 structure (cartilage, muscle, etc.), and m1 repre sents the mass of the button 5 and the eiiective mass of the armature 1. C1 represents the com pliance of the armature, that is the reciprocal of the deflection per unit force applied between the 70 button and the transducer unit, C: represents the compliance due tothe elastic band which sup ports the unit at the neck, and ma represents the mass of the unit, the housing and the covering. AThe resistors r1, rn, ra represent the eiiects of dis 75 t annif/s1 sipation in the several associated elements. The compliance C: is probably so high as to be material even when of used protectingv without the oil armature or other and damping acting negligible, that is Ca can probably be short-cir as an acoustical shield to prevent vrind and ex cuited (omitted) from consideration for -all prac tical purposes. ' ' ternal acoustical 4disturbances from reaching the - armature. The voltage generated by the microphone is ' proportional to the velocity- of the armature with respect to the other elements of the unit, and is A . I y5 In the embodiment shown in Fig. 10, van an nular piece 24 of rubber or other resilient` material is placed between the armature ‘land the cover piece 2|, `and the central pole piece I0’ is drilledshv represented in Fig.'5b as v1, the current flowing in the C1 branch. _'I‘he _form of the vfrequency re _and threaded to receive a cylindrical plug 25 of 10 ' sponse characteristic with _constant impressed resilient material, such as rubber or -“glyptal”, velocity depends upon the driving impedance of and an adjusting screw 26. .Pressure applied ' the neck, Zo. Ifa piston vvibrating at> constant through the plug 26 tends to bend the armature velocity be used for driving purposes, a curve of upward, and this is resisted by the ring 24. >By 15. the type shown in Fig. 6 is obtained for the de altering the dimensions of the ring 24 and the 15 scribed unit, or pair of units. This curve is chiefly position of the screw 26, some control of the characterized by a resonant rise in output near -length of the air gap is obtained. The upper ringV ' 300 cycles and another near 3500 cycles. The 24 may be omitted if the armature 1 is given an first is due ~principally to resonance between the initial adjustment to lie against the pole piece 20 armature compliance Ci and the mass- ma of the l0', the stiifness of the armature itself being then` 20 unit. The upper ~resonance point at 3500 cycles relied upon to oppose the thrust of the plug 25 as arises principally from resonance between the the screw 26 is adjusted to obtain the desired mass of the armature m1 and the compliance C1. air gap. Damping may be obtained, as previ The exact -shape of the characteristic curve may ously described, by materials placed in the space be controlled by adjustment" of the mechanical. between armature '| and cover piece 2|, or by the 25 10 , 3* > impedances. The low frequency response, for ex viscosity of the resilient materials 24. 25. ` ample below 1000 cycles, may be controlled by the Another method o_f damping is >to construct the lower resonance. ; This, in turn, can be controlled armature '| in laminar form, using a strip of by the mass me of the u_nit and the armature com damping material _between two resilient strips of 30 pliance C1. The latter can be modified without 4metal. The strips may be pressed or cemented'30 varying the upper resonance byvarying the-Width into an integral whole which may be mounted in of the armature. The lower resonance peak can the same way as a solid iron armature. thus be moved up and down in frequency to secure The magnetic systems so „far described have> an augmented response at any desired frequency, comprised" a pair of short bar magnets 8, 9’ 35 with a sharp decrease in response below that mounted on the ends of a back piece having an 35 ' ' -frequency, as shown by the solid line curve A integral central pole piece Ill'. As shown in Fig. of Fig. 6. This particular curve represents the 11, the back piece Ill‘ may be a single- permanent performance of a microphone having the follow magnet having an inserted pole piece I0", with ing characteristics;- armature 'i of silicon steel, short bars of soft iron'9“ at the ends of the bar Y40 0.8 x- 0.5 x 0.014 inch; button, white pine, mass= magnet. The magnet. lilEl is magnetized in, a Jig 40 _ » 0.15 gram; mass of unit=15 grams. or fixtureA so that like .poles (north poles N as 'I'he upper resonance can be controlled, as de indicated in the drawings) are at opposite ends a scribed above, by varying the length and thick of the bar and the opposite poles S are in contact ness of the armatupé '|. It is not always desirable adjacent the pole piece Inh. This construction to have a high sharpV peak, such as is present in` has the advantage thatV a longer magnet, and 45 curve A at about 3500 cycles, >and this can bev correspondingly higher coercive forces, are ob avoided by providing damping in addition to that tained. Due to the extra length of the magnet, ' > arising from the internal viscosity of the metal itis sometimes possible to obtain the required and the cement used to fasten the button to the Acoercive force with tungsten steel in place of 50 amature. One of the simplest and most eil'ec cobalt and like steels.y The separate soft iron end 50 tive methods of damping is to -insert a drop or pieces 9* can bejreplaced by integral extensions two oi’ oil in the air gap between the Apole piece of the bar magnet HP. . lli' and the armature 1. Dotted line curve A' of Fig. 12 illustrates another structure which `of Fig. 6 illustrates the >effect of a drop of oil, of fers certain advantages. In_ this construction, 55 viscosity 30 in the standard commercial scale for the button and armature are formed in one piece, 55 automotive lubricating oils, inserted in the air the button being pressed out as a boss on the y gap. The oil is permanently held in‘place in the armature strip 1’. air gap by capillary attraction. ’ the button becoming loosened. Also by utilizing - This avoids the possibility of - Another transducerconstruction which is par. ' the space below the .button section, a greater’ ticularly adapted for oil damping is shown in Figs. number of turns can be .accommodated on the oo 7 to 9.~ The general construction isas previously coil Il', thus increasing the voltage output. A described and parts which are, or may be, sub method of adjusting the air-gap is also shown .stantiaily identical with the elements of Figs. 1,v which may be applied to the other constructions 2 and 3 are identified by corresponding vreference .as well. This is accomplished by sliding the cen, numerals. A cover plate 2| is arranged parallel _tral pole vpiece |0° through the back plate IIId 65 to the armature 'l and spaced therefrom by a few and fastening the pole. piece by means of a set . thousandths of aninch by shims 22, 22', the plate screw 26'. _The other parts of this construction having a central hole through Awhich the button 5 are designated by the reference numerals of the projects. Damping material 23 is placed in the previous »iigurea v space between the plate 2| and armature '|, and A complete electrical system incorporating the 70’V ì ` this is preferably oil ybut may -be cotton, cloth ‘microphone is shown schematically in Fig. 13. soaked inV oil, rubber, felt, “glyptal’”, etc. When oil is used, it is held in `place by capillary attrac tion. The cover plate 2| _isxpreferably metallic, 75 about if inch'thick, and it presents> the advantage Only one unit is shown as the microphone M, and this works into an am'pliiier 21 of the >type which is described in detail lin copending application Ser. No. 54.347; the circuit diagramfappearlng as Fig. _75 I" 2,121,781 4 4 of that application and its frequency response characteristic as Fig. 5. The overall frequency response of the microphone and ampliñer, when the microphone unit is clamped and driven ‘by> a constant velocity piston, is shown in Fig'. 9 of V5. A throat microphone of the electromagnetic type comprising a permanent magnet, a yoke and pole piece, a coil surrounding Asaid pole piece, a resilient magnetic strip positioned to complete the magnetic circuit except for a. small air-gap between said strip Aand said pole piece, said re« the earlier application. The amplifier 28 Vmay siiient magnetic strip being mechanically reso nant between >2500 and 4000 cycles, and means for transmitting vibrations of the throat to said re work into a radio transmitter or, as shown. into a transformer 28 and headphones 20. - I am- aware that microphones operating on >the 10 electromagnetic principle were proposed as early as 1884, but the constructions herein described silient strip.- I claim: ’ resilient magnetic strip .positioned to complete the magnetic circuit except for a small air-gap between said strip and said polelpiece, said re _ siiient magnetic strip being mechanically reso ' 1. An electromagnetic transducer comprising an E-shaped ileld magnet structure magnetized to have end poles of one polarity and an inter# 25 mediate pole of the opposite polarity; an armature consisting of a resilient strip of magnetic material extending between said like end poles and over but spaced from the intermediate pole, a coil on the intermediate pole, and means consisting of a 30 fluid medium between said resilient strip and a rigid member for damping the vibrations of said resilient strip. ' 2. An electromagnetic transducer as claimed "as v type comprising a permanent magnet, a yoke and pole piece, a coil surrounding said pole piece, a have novel mechanical and'electrical character istics which particularly adapt this type of mi crophone for use as a throat microphone. It is to be understood that the invention is not lim ited to the exact constructions herein illustrated and described as many variations which will oc- 1 cur to those familiar with this art fall within the spirit of the invention as set forth in the fol 20 lowing claims. » 6. A throat microphone of the electromagnetic in claim 1, wherein said fluid medium of the damping means is in the, gap between said re silient strip and the intermediate pole. 3. An electromagnetic transducer as claimed nant above 1500 cycles, means for critically damp ing the vibrations of said _resilient strip, and means 20 for transmitting vibrations of the throat to said resilient strip. l 7. In a contact microphone adapted to trans late vibrations of the throat due- to the voice and of the ,type comprising a vibration element having compliance and mass. and Vsupporting means. 2,5 having mass; the method of reducing frequency " distortion due to the mechanical vibratory char-r ' acteristics of the throat which comprises tuning the natural vibration frequency due to the co operation of the mass of said supporting means and the compliance of said vibrating element to a frequency between 100 and 1000 cycles, and 30 simultaneously tuning the- natural frequency due to the cooperation of the mass of said vibrating 35 element and its compliance to a frequency above 1500 cycles. ' » 8. A throat microphone comprising a resilient vibration member to which the vibrations of the throat are transmitted, and means for supporting said vibration member on the throat, the com 40 in claim 1, wherein the rigid member of said damping means comprises a relatively rigid cover 40 plate extending in spaced relation over said re rpliance of said resilient vibration member being siiient strip. ‘ , 4. A throat microphone of the electromagnetic resonant with the mass of said supporting means at a frequency ofthe order of between 100 and type adapted to be actuated by mechanical vibra , tions of the body due to the voice, said microphone 1000 cycles, and said resilient vibration member K 45 comprising a permanent magnet, a yoke and pole> being resonant at a frequency above 1500 cycles. 9. A throat microphone as claimed in claim 8 piece, a coil surrounding said pole piece, a re silient magnetic strip positionedto complete the in combination with means damping said vibra tion member at said resonant frequency above magnetic circuit except for asmall air-gap be tween said -strip and said pole piece, said re 1500 cycles.> 50 STUART BALLANT'INE. silient magnetic strip being mechanically reso ,- 50 ' nant above 1500 cycles. and means for transmit ting vibrations of the throat to said resilient strip.