US2638508A - Vented casing and vaporproof enclosure for sound transducers - Google Patents

Description

May l2, 1953 v R. w. CARLISLE 2,638,508

VENTED CASING AND VAPORPROOF ENCLOSURE F OR SOUND TRANSDUCERS '3 Sheets-Sheet 1 Filed Aug. 31, 1950 INI/EN'I'OR.

TTORNEY May l2, 1953 R. w. CARLISLE 25638503 vENTED CASING AND vAPoRPRooF ENcLosuRE FOR souND TRANsDucERs Filed Aug. 31, 195o s sheets-snee: 2

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, R. w. cARLlsLE 2,638,508 vENTEn cAsING AND vAPoRPRooF ENcLosURE FOR SOUND TRANsDUcERs May l2, l/953 Filed Aug. s1, 195o 5 sheets-Sheet 3 fz- 5.15. FE- 5.

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lll/ll l IN V EN TUR. l? W. kfz/.ne

Patented May 12, 1953 Richard W. Carlisle, Elmsford, N. Y assignor ,to

ration of New York' This invention relates to sound trensdncine devices ,soon as microphones used .es part of .ocompact small nearing sid amniier Worn 011 the body of the user, although tine general Drill- ,cioles of the invention are also applicable to other .sonno .tronsdncine devices es coinrnenciol microphones .or telephones More .sne-

-cicaliv, the invention is directed. to snch Sound -tronsduoine .devices in :which .o vibrntorv diaphragm is` .connected to .a vibro-.electric troneducine .element .suon as. a ypiezo.-.electric .crystal transducer element which .trnnsduces .electric potentials .into mechanical forces or mechanical forces into electric potentials.

Arnone the objects of the invention is .a sonnd transdncine device .of the foregoing type in which the vibratori' diaphragm .forms nari .of on eX- trernely microphone ,cavity .enclosure Within which Athe vibro-electric transducer element is ino nted, Aand in which the cavity enclosure is provided with vent opening portions which reduce the great. stiliness .o f the body .of air conn ed .in the cavity enclosure and secure the desiren microphone .son ivmr the-low frednency range, while also providing a pro ivelv .denied vapor-prooi enclosure for the humidity sensitive vibroelectric element- 'Ine ioresoins and other objects .of the invention will be best understood frorn the followine descriptionof .erernniications thereof, reference being .had to the accompanying drawings -vvliereini Fig. 1 is s greatly .enlarged sectional view., .alone lines of L I .of Fia 2, ci one forni of o neerins ein vvinicronnon-e ereinnliivine the Principles of the invention;

Fig. l-A is an elevational view of the narrow ,side'of a hearing aidamplier, shown in actual size, vvith parts of the" housing in cross-section, to expose a "microphone heldbackbf the sound perviousY front-Wall portion of the amplifier housing;

'Fiel ..2 is. o cross-sectional view oi the microphone 'along lines 244'2 offFigfl';

n Fig. 3 is a cross-sectional ,view along lines 3-3 ofFg-z; y .Fisis .o cross-.sectional view alone lines A qofmg 1;.

Fig. 5 is a front View of vtlie vibratorsr diaphragm of the microphone:

lSlnrotone Corporation,

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Fig. 6 is a vfront -vievv Kge'ri'erally similar to that f of Figure 2 of another form lof a ,microphone of the `invention,,the feront yvall andthe major -part or the diaphragm and diaphragrnbarrier removed .t0 otros? the interiorof mentionnent t' vg, corpplicatioo August 31, 1950, serial No. 182,490 2 claims. 01? ire-fno) 2 cavity enclosure with the elements mounted iihieoli;

Eig. 7 is a side View of the microphone shown in Eig. 6 with the upper portion in cross-section alone :lines 1- l of sie. o;

Fig. 8 is a cross-sectional enlarged detailed view of a part of the microphone shown in Fig. 6 sione' lines ti- .8 thereof; v.

[Fig: 9 is a `iront View of the microphone similar to Fig. 6 with only a portion of the front cover and the vibratory diaphragm removed; and

Fig. 10 is a cross-sectional View of the microphone or" Figures 6 to 9 along lines Ill-, of Figure 9- Hesnne no microphones .which ere uses es a part oi a high-gain amplifier hearing aid have to operate under conditions utterly different from those encountered in other microphone applications. This is due to the fact that ythe amplifier housing in which the microphone, is hlled' hat?? t0 l?? WQIH 1110i@ "01' 1595s hidden undef the clothing of the user Where it is exposed to humidity which greatly affects its performance,

`nerA components includinsT the switches and rheostats as Well as the batteries which supply cathode heating current and space current to .the amplifier tubes. This makes it essential t-o Aleep the space occupied by the microphone to .a minimum, While et tnesome time designing in such a way as to cause it to operate with a desired high sensitivity over the principal part of the Aaudio frequency range essential for the intelligible reproduction of speech These requirements impose very strict limitations on the construction of .such nearing eid microphone; since .in order to obtain nich sensitivitythe vibro-electric transducer element must be driven by a relatively large vibratory diaphragm .exnosed to Isound propagated in the `sinrounding air.

If an attempt is made to provide a fiat micro- 4lonone' cosine having sncn vibretory diaphragm With a microphone cavity sealed against entr-y 'of humid air, there is encountered the problem of assuring that the diaphragm Shall loe able vto withstand the highforces, of aboutZ` to 5 pounds,'caused by'normal variations in theatelectiet-type mospheric pressure to which it is exposed. This makes it necessary to provide a very strong and stiff diaphragm structure which, for its small size, is inherently insensitive to sound propagated in the surrounding atmosphere. As a result, such microphones would have to operate with the greatly reduced sensitivity in the frequency range below about 1000 cycles per second, thereby greatly detracting from its usefulness as a hearing aid microphone.

In accordance with the invention these limitations are overcome by providing microphone cavity enclosure formed by the vibratory diaphragm and the associated small compact microphone casing with vent opening portions which equalize the air pressure on both sides of the vibratory diaphragm for maintaining it in the desired vibratory position and securing the desired transducing sensitivity of the microphone in the lower part of the speech frequency range,

and interposing between the vibratory diaphragm and the cavity portion within which the piezoelectric crystal transducer element is held a limp barrier diaphragm which is hermetically joined tothe rear wall of the microphone casing to form therewith a sealed vapor and humidity-proof enlclosure around the transducer element without materially detracting from the desired over-all 'sensitivity and frequency response of the microphone. What was said above about the harmful effect of humidity on piezo-electric crystal transwardly tapering diaphragm II, having a circular peripheral portion l2, the edge of which is sealed and held affixed to the iiange I3, of the circular rim i4 of a at casing wall I5 of the microphone so as to form with the diaphragm I I a at microphone cavity I6. lThe diaphragm I I is light, and 'its'outwardly tapering conical shape gives it the desired stiffness so that substantially its entire exposed area will vibrate when excited by sound propagated in the air space in front of the coni- "1"' element 2| shown in the form of a piezo-elec-ai;

trical crystal bimorp-h of generally rectangular, at shape, and extending immediately above the '-innersurface of outwardly oiset wall portions I8 ofthe casing wall I 5. In the particular offset form of the microphone of the invention shown,`

the transducer element 2| is a conventional twister-type bimorph of Rochelle salt crystal having the usual surface electrodes. Three corners of the piezo-electric transducer are connected through elastomer pads 23 to the inner surface ofy the casing wall portion il. The

'fourth corner portion 22 of the piezo-electric crystal transducer 2| has a driving connection 3'1 to the generally central drive portion I7 of the As an alternative an conical diaphragm II.

condenser structure may be mountedwithin the cavity and connected to the diaphragm for actuation thereby.

In'order to reduce the overall thickness of the just enough space for housing therein the conical Yvibratory diaphragm II and the transducer ele- 'ment 2|. As Aa result, the thin body or layer of casing has high stiffness which cuts down the "microphone I 0 to a minimum, the thickness of "themic'rophone' cavity I6 is kept down to provide `air confined in the cavity I6 of the microphoner microphone sensitivity in the low-frequency part of the principal audio-frequency range important for the intelligible reproduction of speech, and particularly in the range of about 1,000 cycles and below. To overcome this difficulty it is essential to provide a vent opening from the microphone cavity to the air in the outer space. On the other hand, it is essential that the humidity sensitive transducer element of the microphone, which in most cases is made of Rochelle salt crystal or a similar humidity-sensitive piezoelectric crystal substance, be enclosed within an enclosure which prevents humid air from reaching it.

In the microphone of the invention, its sensitivity in the low-frequency part of the audiofrequency range, is raised by providing the vibratory diaphragm I I with vent opening portions in the form of a small hole 24 which equalizes the air pressure in the cavity I6 with the outer atmosphere and maintains the vibratory diaphragm in the desired vibratory condition irrespective of variations of the outer air pressure. Such vent opening portion 24 raises the sensitivity of the microphone in the low frequency range between about 300 to 1000 cycles per second, so that notwithstanding the small thickness of the acoustic air cavity I6 of the microphone structure, its sensitivity is as high as that obtainable with bulkier microphone structures.

In accordance with the invention, the cavity part housing the transducer element 2| is sealed against entrance of humid air by interposing between it and the inner side of the vibratory diaphragm I| a limp vapor-proof barrier diaphragm 3i having a circular peripheral portion 32 sealed in a vapor-proof hermetic manner to the circular casing wall flange I3 to which the periphery of the vibratory diaphragm I I is secured. The portion of the barrier` diaphragm 3| extending between the drive portion 22 of the piezo-electric crystal transducer element 2| and the central drive portion |'I of the diaphragm |I, provides a motion-transmitting connection therebetween, being united thereto as by cement.

Without thereby limiting the scope of the invention, there will now be described one specic manner for providing a driving connection between the driving portion 22 of the vibratory diaphragm across the portion cf the barrier diaphragm 3 I extending therebetween then forming part of the driving connection. A rectangular strip 35 of fibrous material such as resin-impregnated` paper, is cemented over the corner drifve portion 22 of the transducer crystal element 2|, shellac being a good cement for this purpose. The outer surface of the cover strip 35 underlying the drive portion I'i of the vibratory diaphragm kI| has secured thereto a facing portion of the `is connected to the drive portionv22 of the transducer structure 2|, is slightly eccentric relatively to the periphery lof the diaphragm, to enable the use of a larger, more compliant crystal transducer structure 2| which matches better the low mechanical impedance of the small cone, and in- Vcreases the sensitivity of such small hearing-aid microphone To the outer side of the barrier diaphragm stable, commercially available cement. I l "securing the' drive rod 3'1" tothe4 driveV portion 'portion 3l secured to the4 drive portion 22'o`f the 'transducer nement 2 there* is" securedthie enlarged neadas of a snort' rivet-lire roc' 31 etang "into an opening f'c'irmed2 in`v the central drive por- "tionL Il' of the conicalAv viloratoryv diaphragm il, the' rod head 3'5 being *secured* to' the" underlying driving portion of the barrier diaphragm 3 land to the transducer element 2i by a strorigjand After 22 of the transducer element andthe' overlying lsmall portionofthe barrier ydiaphragz'n 3l previ- Iously secured thereto,v the"Y vibratory diaphragm IH isv placed with `theholz-r of its central drive 'portion-"IT over th'e drive-rod 31, so asY to surroundthe same: Thereupon: the periphery lf-2 of v'the vibratory diaphragm Il'4 is cemented to the 'periphery' of the barrier diaphragm 3 l overlying theflange- 13' of the microphone casing wall i5 to Which'- the periphery of' the barrier diaphragm -1H Was previously united by' astrong, stable cement; similar to that used forv cementing" the periphery lZof' the vib-ratorydiaphragrrr i I- there- After theperiphery of' the vibratory diaphragm i has been thus united by cementihgfto the flange i3" of the microphone casing wall' l5, the central drive portion H' of the diaphragm surrounding the drive rod 3i"y isunited theretoV by applying a' quantity of cement 38 thereto, so that it iills thespace between the opening of the drive portion Ily of the vibratory diaphragm and the drive rod surrounded thereby. and rigidly unites the 'samefto provide a rigid, stable driving connection between the drive portion 22 of the transducer velement andt'he drive'portion il. of the Vibratory diaphragmvacrossthe'portion ofthe barrier diaphragm 3 lr united to them.

- As explained above, the barrier diaphragm 3l' is-suiciently limpan'd looseand'` has such high Vflexibility that it movesfreely when the drive portion 22 of the crystalivibrateswith the'vibI ratoryA diaphragm" I'I, wit-hout substantially im- -peding their vibrations; In the practical construction of' microphones, it was foundthat thin valuminum foil' may be eiectively used both for the vibratory diaphragm Ilv and for the limp, loose,A barrier diaphragm 3 l To'v protect the hermetic cement'seal between vdiaphragm 3l, and the' circular flange' l3- of the relativelyrigid microphone casing l5; therefis Ipl'aoedover they several cementedperipheral edges fofl the same; a channel-like member 4I, which is v crimped and. clamped over lthe peripheral border portion of the circular peripheries. of. the'r diag phragms' IlA and 31|;v and the casing Wall flange 13; In the form shown, the channel-member :il

- forms the circular peripheral angeportion of a sound-pervious grille `wall 42 placedover the outer Aside of the vibratory diaphragm l"l,.so as to'prot'ect its fragile foil structure against mechanical contact. lThe grille 42 has ya1 relatively large opening 43 through which the vibratory` diaphragm l l isacoustically coupled to the'air space infront of it, to provide for sound transmission therethrough;

As-shown in Fig. l, an additional Washer i8 iof agyieldable material-such as nbre-impregnated rresinous sheet materialtor tough rubber-like -material, isplaced-:against the outer peripheral surface region: l2v of the vibratory diaphragm lll,

so"that it'y isf yieldablyy clamped? byv the'f'acing peripheral portion of the grille wall 42 whe`n`- its iingell fisclampingly--crimpeclbver' the 'peripheralfcircular edge-regione ofrth'e vibratory dia- 'if' at; me are 1n a prenne-rainnricanone arti-1e vention,v the casing wall l5y ofthe microphone; as

'vv-,eul as the gime 42'; are aaieepf Shea hummm shaped by conventional cu ing an forming operation. The gri-llewith 1 schannelf' mber 4?! is pla "edl over the periphery ofthe Vhratoryv diaphragm H', and the underlying periphery f the barrier` diaphragiri 35i",V bothLv of" have been previously secured by-cementig'in an hermtical- 13/fsea1emanner'td me casing wat aange f3, whereupon; the rear edgeofv th'ecylind'ri'cal" charrnel flange '4T of-v the grille is criirrpedI over the rear surface" of the casingfwa'll flange,- to pro'- vide a protectivev channellike seal around the peripheries-ofthe diaphragme Hf and 31' and the casi-ng wall harige i3; and assure a positivev and stable hermetic seal therebetween.

'Ilo provide electric terminal connectiond to the-vibro-electric transducer element ZI of the micro-phone, the' casing wall has secur'ed to op posite sides of a portionv thereof', twofsheet" metal terminal tabsv 45, 4T, as by ai rivet 4G extending hl'Ollgh' the Casing Wall, lio:v provide' y2th:'llliflakte hermetic seal therebetween In additiontwo other metal terminal" tabs 5| 52 aref secured' to another portion of thecasing Wall I 5- by ai' rivet 53 passing through a hole off the Wall, insulating Washers and spacers 54, 55j insulating the two tabs 515, 52 and thervet 53 from" the' metallic casing Wall |5l The' insl'ilati'n'gL spacers 54',y 55

'the insulatingV spacers; to assure thatv under all 'conditions the holes through which the terminal rivets 46 and 55 pasfs;V are at? alltimes'herrnetical 1y'v sealed to preventl entrance of moisturel into thecavity part Within which the humiditylse'ns-itivetransducer element' is operatively mounted.

To the lnWa'rdt-ermi'nal tabs-'47, 52` areY SieClid, as by soldering, terminal e1ements'51, 58 of'aluy'rriinum foil; for instance', secured to thelusualopposite external surface electrodes-of the vibro- 'elec'tric transducer element 2-1.'

Furthermore, stripe of insulating material-59,

'such' as resin-impregnated insulating material,

are placed against thev oppsi-te surfacesy of the `terminal lead 58 and the terminal tab- 5'2` connecting theinsulatingly" supported' surface electrode of thetransducer element' 2l to the insulated terminal-rivet 53 through which an insulated'l external terminal connection-is' provided to' the insulated transiuizer` electrode of the tnansducer element 21'. The external terminal tabs 445; 5l, may'thusl be'use'dito provide terminal connections to leads such as'` leads 6I; 6-2, through whichthe transducer elementi! Iisconnected to the amplifier circuit of thel amplifier elements,

including tubes'mounted within the'h'eai'ing aid amplifierfmicropho-ne assembly housed'in a flat casng'63', as shown'i'n Fig. l-A: n

As' indicated' in Figs. 1', 12A and` 4; the" micro.- phone. unit l 0- is" held suspended on' alvibrationdamping',v flexiblesupport 64 shown in i the form j of a" loop` formed olf'hollow tubing'iof rubber-like, ela'strom'er materialstriirig around laplralitypf vgrille opening43to the acoustic space in front of the vibratory diaphragm II, for assuring that the microphone diaphragm is excited bysound propagated intheouter air, and actuates-.the transducer element 2I to generate a corresponding electric output. To the outer surface of the front grille wall 42 of the microphone and the .rear microphone wall I5, are secured spacer strips 12, 12 of a vibration-suppressing material such as sponge rubber, to suppress transmission of vibrations to the microphone I from the walls of the amplifier casing 63 and the amplifier structure, and other elements housed therein.V

vAs shown in Figs. 1, 1-A and 4, van additional thin sheet v13 of plastic material is united as by cement tothefront grille wall 42 of the microphone I0, the sheet member 'I3 extending closely adjacent the rear surface of the sound-pervious front wall 66 of the amplier casing, to suppress propagation of sound from the space in iront of thevibratory diaphragm II of the microphone casing I5 toward the rear space in the micro-- phone amplier casing. In other words, the flexiblesheetmember 13 extending beyond the borders of the front grille wall 42 of the microphone unit, `is arranged to serve as a barrier suppressing propaga-tion of sound from the space in front of the vibratory diaphragm I I to the space in back of the microphone casing wall I5.

dAs'indicated in Figs. l and 4, an additional sound-pervious sheet portion, for instance, of

gauze 15, vis secured as by cement over the opening 43 of the front grille wall 42 of the microphone, as an acoustical damping control and also to suppress entrance of dust into the space between the'vibratory diaphragm II and the grille `wall A42 ofithe microphone.

A- similar soundpervious gauze sheet portion, which is substantially impervious t0 dust, is also shown cemented to the inner side of the sound-pervious casing wall 66 of the amplifier, through which sound is propagated to the space in iront of the vibratory diaphragm I I.

Without in any way limiting the scope of the invention, and in order to enable those skilled in the art to more readily practice the invention, there are given below constructional data for a small,- co-mpact Vhearing-aid microphone with the desired sensitivity and frequency response characteristics:

The vibratory diaphragm I I has a diameter of about 1 inch, and a cone height of about .090 to .12 inch. In general, good results are obtained with a. ratio of diameter to cone height of about /1. The rear space of the microphone cavity extending between the rear wall I5 of the microphone and the barrier diaphragm 3l, has a diameter of about 1 inch, and a height of about .070 inch. In general, good results are obtained with a ratio of the volume of the cavity part confined between the barrier diaphragm 3I and Vthe microphone rear wall I5, tol the total volume of the microphone cavity conned between the vibratory diaphragm I l and the microphone rear wall, of between about 2.5/1 to 1.5/1.

In the microphone of the invention, the barrier diaphragm 3l which provides the hermetic sealLhasan areaat least as great as the entire large dimension or transverse area of the microture at all joints, such as the joints between the periphery of the barrier diaphragm and the periphery of the microphone wall I5, and the joints of the rivet terminals 46 and 53 to the microphone wall I5, readily obtained by applying to them coatings of a moisture-resistant type of wax, of the type used to provide hermetic vacuum sealing. Thus, such wax may be applied to the peripheral surfaces of the barrier diaphragm 3| and the flange I3 of the microphone wall I5, as Well as to the surfaces of the rivet junctions of the terminal rivets 45, 53 to the microphone casing wall I5.

Figs. 6 to 10 show another form of the microphone transducer device I0-I exemplifying the invention. I-t comprises a generally conical outwardly tapering diaphragm II-I having a generally rectangular -peripheral lbor-der portion I2-I which is secured to the flange I3-I of the rectangular rim I4-I of a flat microphone casing wall structure IIE-I which forms with the diaphragm II-I a iiat microphone cavity IB-I. The diaphragm I I-I is light and its outwardly tapering conical shape gives it the desired stiffness so that substantially its entire exposed area will vibrate when excited by sound propagated in the air space in front of the diaphragm I I-I.

The conical diaphragm II-I is shallow and its central portion II-I is connected to a vibratory portion 22-I of a vibro-electric transducer element 2I-I formed of a piezo-electric crystal bimorph of a conventional generally rectangular sha-pe extending ilatwise adjacent to the inner side of the casing wall structure I5I. Three corners of the piezo-electric transducer crystal unit 2I-I are connected by elastomer pads 23-I to the underlying supporting wall structure and the fourth corner 22-I is connected through a drive connection 3'I-I vto the central drive portion I'I of the vibratory diaphragm II-I.

In order to reduce the overall ,thickness of the microphone I0-I, the thickness of the microphonecavity IS-I is kept down to provide just enough space for housing the conical vibratory diaphragm I I-I and the transducer element 2 I-I drivingly connected thereto. Because of the special shape of 4the vapor-proof transducer compartment 30-I, the body of air within the microphone cavity II-I has a lower stiffness relatively to the vibratory diaphragm II-I as compared to lthe microphone arrangement of Figs. 1 to 5.

When the cavity vent opening 24-I is closed, .the

sensitivity of the microphone above 5000 cycles per second is not materially reduced. However, if the vent opening 24-I is closed and the entire microphone cavity IB-I is hermetically sealed, changes in the atmospheric pressure will force the conical diaphragm completely out of shape lwithin a few hours yand abruptly if it is used on an ascending or decending airplane in which it is subjected to sudden changes in the air Apressure.

In the particular microphone described above in, connection with Figs. '6 to 10, the vented r9. microphone .cavity `16.-! .is :deemed toiresonate in .the lesionv of about y3,00 cylesner second? thereby increasing itssensitivity in: that region.

vThe vaporproof transducer-compartment BI-i is `@friesea.s small. as rvssibleito; keen ,down theV air enclosed thereby and `thus minimizathe vexcursions-ofthe limpbarrier diaphragm l 3l-l under variations of :theatmospneric pressure- In the form of the invention lshovvn in lfigs. 5 to this is achieved byproviding ,thecas-ngwall structure VI-l of the microphone cavity l'zfl with a vent opening 24-.-l to the .exterior air-while separating the vented part of the microphone cavity from the cavity parthogusingtheltrans- -ducer unit 2| Aby any interposed limp vapor-proof barrier diaphragm ,3l-i. .Y'Ifhclimpbarrier diaphragm I-l has a peripheral portion 32.-;I sealed by-a vaporproof sealing cement in a Vaporfproof hermetic manner to compartment Ipartition wall portionsll-.I of the microphone casing struc.- Iture so las to form with the barrier diaphragm 3|-AI a lvaportight compartment. enclosure 31h-l around the rtransducer unit 2 I-I.

The portion vof the barriervd-iaphragm 31-.1

extending betweenthedrive portionJZ-l ofthe piezo-electric transducer unit `2li-i and the central drive portionw-i'I-l of the y.diaphragm H-i provides a motion 4transmitting driveconnection therebetween.k In -the form-shown, .the outward surface of the ydrive portion. 2;2-l of the .transducerunit 2 I -IA is united, as bya goodinsulating cement, to the adjacentoVerlyi-ng portion ofthe limp barrier diaphragm 311-1. Tozthe :outer side of ,the limp :barrier diaphragm 3i-I, .which iS cemented and united .te theunderlying :drive p0rvltion .Z2-.I of the crystal transducer Zi-l, is secured one arm of ia stripfshaped drive rod Sl-i thecther arm of .which passes through a slit in the central portion. ll-l of .the .vibrator-'y dia. phragm :l I-I to `which it issecuredasfby sealing cement 3?.-2. This arrangement .assures that the portion of the ybarrier diaphragm overlying `the corner drive portion'22.-I of the transducer crys- -talrunit 2 I ,forms *la substantially -rigidpartof the driving connection to theldrive portion I'Vi-I of the vibrator-y diaphragm I l -l -of the microphone.

By making the drive rod 37st in theform Qf aV strip there is provided transverse flexural 00.11.1- pliance in the driving connection between the crystal transducerunit 2 I-i and thevibratorydiaphragm li-l in a direction transverse tothe directionof the transmittedudriving forces. This arrangement reduces the overall stiffness of the Vibrating syst-@mand increasesthe efciency and the nOverall.sensitv..ity f the microphone es an acoustic transducer device.

The .compartment partition wa-ll. l I-I, to .which the peripheryof the limp barrierdiaphragrnf3.1?! is hermetically united, may-be gformed of integral portions of .themicrophonecasing structure wel. In the form shown, the compartmentpartiticn wall 'Het :forms aperipherallange of therim I-2 of a separate inner compartment Wall lil-l constituting with the barrier diaphragm 3i-I the vapor-proof enclosure compartment Sii-I of the transducer unit 2 i-i.

As in the microphone of Figs. 1 to 5, the Vapor proof transducer enclosure compartment Bil-*i With the associated compartment Wall 'lli-i occupies only a small part of the volume of the microphone cavity l-i In the form shown, the compartment Wall 'lll-i is shaped to fit against the border rim of the microphone casing wall i-l and to support on its inner side the transducer unit .2 l-l in a position in which its driving portio n,. 2 2.| Ikis approximately adjacentto the (center portion-of the -vibratory diaphragm. v The com partment wall fit-l A is Vformed .out of sheetmetal toconstitute a relatively. rigid structure having y a peripheral flange li-l to which the peripherypl the limp ybarrier diaphragm .3i is united by f -a vaporproofcernent to form a-hermeticallysealed enclosure around the transducer `unit 24.

This Iarrangement makes it possible .to rst mount Aand assemble the transducer unit .2l-Ul.v and the asseciatedparts in their operative-positions Within thel compartment Wall 'ill-l anduto there.- after yseal theperi-phery of the limp barrier-.diaphragm 3 if-lv ina vaporproof lhermeticmanner` to the kflanged rim ,T2-J of 4the compartment rwall 1li-l and thereby form a vaporproof enclosure around thejpiezelectric transducer -unitZI-I. The sealedfenclosure compartment cas-,ing 1li-.I .-is suitably secured infits position withinrnicrophone cavity l6-l to the casing wall iii-l Iinthemesition shownin which the center vportionfof ,the vibratory diaphragm may vbe anixedftoathefdriye rod Blei .previously amxed to the abarrier diaphragm portion overlyingY the driving portion 7a2-.fl

f ofthe piezo-electric trausducerunitZ l-landhe-ld in vibratory position Within the. compa-rtrnent'f-vfall lll-1 v The compartment wall lli-i is :shapedxso-asto provide an enclosurecompartinent of Va :miniF mum thickness at the region where its enclosed transducer unit 2i-| is connected through the driving rod S'l-l to the vihratory diaphragm lat-fi, To achieve aminimum overall thicknesafthe portionof the compartment Wall 'iii-,I -underiyingthe is offset at 'lil-2 :in outward direction andfisfheltl at the same level-as the main microphnecas# ing Wall l5-I Within an `opening-thereof (Eig.:10);

=In the form shown the compartment wall 21tr-'i' is held in position `on the'rnicrophonecasing-wall vlli-+I by two `tail Aportions 'i5-i, forming .integral extensions of the Wall rim Hl-L and extending through slits in reentrantwalldepressions lie of the microphonecasing Wall IE-i (Figs. 6 and-'7).

The tail portions 'i5-l may be Yafixed Within the slits ofthe microphone casing -Wall portions i5-3 by twisting their outer ends andorbyplac.q ing over the interfitting parts of the depressed wall portions iti-3 lumps l5-2 of sealingcement.v In addition, sealing'wax cement isalso applied at l0-3 to the junction region betWeen'theoi-set portion A'iii-2 of the compartment -Wall 21B-i and the adjoining sealing opening region ofthemicrophone casing Wall i'-i (Fig. l0). f

The microphone I0-| shown is also provided with a novel arrangement of terminal lead connections 'from exterior circuits to the piezo-elec# trictransducer unit'2 i-2 held enclosed Within the vapor-proof enclosure compartment' 'S0-I. Inthe form shown, two insulatecllconductor Vleads l8f|i, 82-I pass through small perforationsof -the compartment Wall rim 'i2-l 1into the interior cavity space B-i. The rim openings through which the tWo insulated leads 8l!, 8i-2 enter the sealed compartment interior Stiel are hermetically sealed by applying thereto and to the adjoining lead portions an insulating sealing Wax cement of a type which provides a stable hermetic vaporand moisture-proof seal to assure that the vaporproof enclosure provided by the compartment wall 70-l is fully maintained.

A strip of insulating sheet material 33-I overlying the inner surface of the compartment wall 'iQ-I (Figs. 6, 8) has two slits M for retaining in position the free ends 6E-i, -I of the two conductor leads 8||, 82-l from which the insulation has been stripped. A folded tongue extension B'I-l of the insulating sheet 83-l is folded over the end portion of conductor lead 85|, which constitutes the high potential conductor lead, to maintain it insulated from the metallic compartment wall 'I0-l. The two opposite polarity terminal tail portions 8'1-I, 2I-5, 2|-6 of the transducer unit 2|-l are joined, as by soldering, to the underlying stripped conductor leads 85-I, 86-1 of the two conductor leads BI-I, 82-I (Figs. 6, '7). An additional insulating strip 88| is placed over the exposed metallic conductor terminal portions 2l-5, 85-l to maintain them insulated from the overlying barrier diaphragm .3l-l.

The terminal leads 8|-l, 82-I emerging from the rim of the compartment of the enclosure compartment wall 'l0-l are led in a similar manner through similarly sealed openings in the rim l4-I of the microphone casing wall |5-I, to the exterior thereof (Figs. 6 and 7).

Without thereby limiting the scope of the invention, there will be now given further details about constructional features of the microphone invention shown in Figs. 6 to 10. The vibratory diaphragm II-l is formed of a thin aluminum foil Whichis given the required stiiness by providing its conical portion With the generally radially extending channel formations lI-2. The barrier diaphragm 3I-I is formed of similar thin aluminum foil, and made sufliciently limp and loose and of such high flexibility that it moves freely when the drive portion 22-l of the crystal transducer 2| vibrates with the vibratory diaphragm Il-I, without substantially impeding their vibrations. A protective sound pervious grill .wall 42-l is placed over the outer side of the vibratory diaphragm II-l to protect it-against exterior forces. The grill Wall l2-l is secured along its periphery 42-2 to the flange 1| -I of the microphone casing wall |5-l over the periphery of the vibratory diaphragm cemented thereto. Openings 42-3 in the grill wall 42-l permit free propagation of sound from and to the vibratory diaphragm and a gauze layer 42-4 cemented over the openings 42-3 suppresses entrance of clust and foreign matter into the interior. The periphery of the grill wall l2-I is aixed to the the periphery 'll-I of the casing wall lli-l by a sealing cement Without any additional crimping junction, or with a crimping junction such as shown at 4l (Fig. 1) for the microphone of Figs. 1 to 5.

Without thereby limiting the scope of the invention and in 4order to enable thoseskilled'in the art to more readily practice the same there are given below constructional `data of a1 small compact hearing aid microphone of the form shown in Figs. 6 to 10, having the required sensitivity and frequency response characteristics:

The microphone cavity IB-l had lateral di- 12 mensions v1 x H inchand a depth of 1/8 inch. The vibratory diaphragm I I -I had a cone height of about .065 inch. iThe crystal transducer unit was fg x '1/2 x 12 inch in size. The other dimensions are apparent from the drawings, Figs.V 6 to 10.

Various other modifications of the invention will suggest'themselves to those skilled in the art. It is accordingly desired that in construing the breadthbf the appended claims, they shallvnot berlimit'ed to the specic details shown and described in connection with the exemplications of the invention.

I claim:

1. In a sound-transducing device such as a microphone fora hearing air small enough to inconspicious Wear on the body of the user: a generally fiat relatively-rigid cavity wall structure; a vibratory diaphragm having a periphery joined to said Wall structure to form therewith an acoustic cavity; a generally flat vibro-electric transducer element held within said cavity and having a portion mechanically connected to a vibratory portion ofV V-said 'diaphragm to form therewith a transducing system which transduces vibratory forces imparted to said diaphragm into electric Outputor vice versa; a light, substantially limp' metal barrier diaphragm interposed within said cavity between said vibratory diaphragm and said transducer element; said wall structure having a continuous Wall regionY surrounding said transducer element; said lbarrier diaphragm having ya continuous metallic peripheral region hermetically joined to said continuous Wall region of said wall structure and forming therewith a substantially vapor-proof hermetically sealed transducer compartment Within ,which said transducing element is held; the cavity part of said cavity extending outside saidtransducer compartment having vent openingV portions for equalizing the air pressure in the cavity relatively to the outer atmosphere and securing the desired sensitivity of said transducing system.

2. In a sound-transducing device as claimed in claim l, said wall structure having a wall member separable from other parts of said cavity wall structure and having said continuous wall region hermetically joined to the periphery of said barrier diaphragm to form therewith said vapor-proof transducer compartment.

RICHARD W. CARLISLE.

References cited in the me of this patent Massa e Mar. 27, 1951

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