US2927976A - Acoustic signal transducers - Google Patents

Description

March 8, 1960 H. A. PEARsoN 2,927,976

ACOUSTIC SIGNAL TRANSDUCERS Filed Nov. 17, 1958 2 Sheets-Sheet 1 March 8, 1960 H. A. PEARsoN AcousTIc SIGNAL TRANsDUcERs 2 Sheets-Sheet 2 Filed Nov. 17, 1958 INVENTOR United States Patent ACOUSTIC SIGNAL TRANSDUCERS Harry A. Pearson, White Plains, N.Y., assignor to Sonotone Corporation, Elmsford, N.Y., a corporation of NewYork Application November 11, 195s, serial No. 714,439

8 Claims. (Cl. 179-114) This invention relates to acoustic signal transducers of the type described in U.S. Patent 2,432,424, which transduce acousticV signals into electric signals or electric signals into acoustic signals. More particularly, the invention relatesto miniature size transducers of this type, the volume dimensions of which should not exceed about 3;/16 X 3/e x 1/2, so as to make it possible to combine two such transducers, one operating as a microphone and the other as a receiver, together with all operating components of a multi-stage transistor-amplifier, into a minute volume fitting into a temple of an eyeglass frame or into a -tiny casing iitting behind the outer ear o1' Within the cavity of the outer ear of the user.

In such acoustic signal transducers, an acoustic diaphragm is connected to drive or be driven by a flat ferromagnetic armature or reed which is surrounded by a spool with transducing windings and is arranged to vibrate between one or two pairs of closely-spaced opposite poles of a ferromagnetic core for operation either as a microphone or receiver in transducing vibrationsof an acoustically excited diaphragm into` corresponding electric signals and vice versa. For eicient operation of such miniature transducers, the tiny at reed mustv vibrate within a tiny, flat central spool compartment freev from interference by the closely-spaced adjacent compartment walls; Minia= ture size microphone and receiver transducers of this type suitable for tiny transistor-amplifier hearing aids, present critical operating and space limitations, and they'require careful and-relatively difficult assembly by specially v trained, highly skilled personnel. p

Among the objects of the invention' are miniature transducers of the foregoing type, embodying, features which materially simplify the assembly and assure properly aligned assembly ofthe tiny transducer components into the composite, efficiently operating transducers, Without requiring personnel ofl unusual skillY for ,their assembly. Among the objects ofthe invention areV also miniature acoustic signal transducers of the'foregoing type, which within a given transducer size willprovide superior response characteristics.

The foregoing and other objects of the invention will be best understood from the following description of exemplications thereof, reference being had to the accompanying drawings, showing all parts greatly enlarged, wherein: l

Fig. 1 is a cross-sectional view of an acoustic-diaphragm transducer of the invention, shown with some of the adjacent elements of a complete transistor-amplifier hear- A RCC relationship of the ferromagnetic elements and the windings of the transducer of Figs. 1-3;

Fig. 5 is a perspective View of the spool with the transducer windings of the transducer;

Fig. 6 is a top view of the armature reed of the transducer;

Fig. S-A is an elevational View of the spool member of the transducer winding; n

' Fig.j5'-B is across-sectional view along line 5-B-5i-B of Fig. 5-A;

Fig. 7 is a top view of parts of the magnetici core assembly of the transducer;

Fig. 8 is a cross-sectional View along line 8-8 of Fig. 7; and

Fig. 9 is a top view of a spacing .shim for the transducer reed.

In Fig. Al is shown an end view of a complete transistor hearing aid the over-all dimensions of which are small enough to form a rear portion itl of a temple 11 of an eyeglass frame 12 worn by the user, as seen in Fig. l-A. The over-all dimensions of the casing 10 of 'the hearing aid unit are such that its volume may be given a shape so that it fits in its entirety--together with the transistor circuits, battery and volume control-within the concha cavity of the users ear between the tragus and anti-helix thereof, such as described, for instance, inthe pending application of F. A. Hermann, Serial No. 705,841, tiled December 30, 1957, and assigned to the assignee of the present application. Within the tiny casing 10 of such complete transistor-amplifier hearing aid are mounted both a microphone-transducer which transduces sound propagated in the surrounding space into corresponding electric signals, and a receiver-transducer which transduces the amplified microphone signals into corresponding sound which is delivered to the ear canal of the user. Both the microphone transducer and the receiverV transducer have essentially the' same transducer stmctures, and they wiil' now be described in connection with-.the acoustic microphone transducer 29 which is shown suspended within the hearing-aid casing i@ in Fig. l, and also in Figs. 2-4.

The acoustic transducer 20 comprises a vibrator-y diaphragm 21 which is connected through a drive rod 22 to avibratory armature or reed 25 of an electromagnetic signal transducer structure having a spool 31 with transducer windings 39 wound thereon, and a cooperating ferromagnetic core structure generally designated 40, The armature reed 25 is of lovwretentivity, high-permeability ferromagnetic material, and is shown as being of fiatV cross-section and extending with its flat surface in a plane perpendicular to the surface of Fig. l.

The cooperating ferromagnetic core structure 4@ comprises one pair of pole arms 4l, lcxtending transversely across and sp-aced from the opposite ilat surfaces of the left end portion 26 of the armature reed 25, and another pair of pole arms 43, 53 extending transversely across and `spaced from the opposite flat surfaces of the opposite end portion 29 of the armature reed 25. The pole-arm pair 41 51 has intermediate or central depressed or inwardly olset pole portions 42, 52 of opposite polarity indicated by N and S signs, with the flat pole sur faces overlying and substantially coextensive with the embraced end surfaces of flat reed end 26 and positioned at a slight spacing on opposite sides thereof so that at reed end 26 is spaced from the two overlying oppositepolarity pole portions 42, 52 of the ferromagnetic core structure 40. The other pole- arm pair 43, 53 has similar central depressed pole portions 44, 54 of opposite polarityindicated by N and S signs, with at pole surfaces overlying and substantially coextensive with the embraced end `areas of the other flat reed end 29, and

Y positioned ata slight-air gap spacing on opposite sides thereof so that dat reed eid 29 is free to vibrate in the air-gap space between the two overlying opposite- polarity poles 44, 54 of the ferromagnetic core structure 40. The two pairs of pole arms 41, l and 43, 53 are shown formed of flat sheet stock of low-retentivity, high-permeability ferromagnetic material, and their respective central poles 42, 52 and 44, 54 are given the desired opposite polarity by permanently magnetized core elements of the magnetic core structure 4). Although each of the two pairs of transverse pole arms 4l, 51 and 43, 53, may form a distinct unit, the pole arms 41, 43 form two opposite integral arms of a generally rectangular ferromagnetic pole frame member 45 (Figs. 7 and 8), and the other two pole arms 51 and 53, which are of opposite polarity, form two opposite integral arms of a similarly shaped ferromagnetic pole frame member 55. The two pole frame members 45, 55 form upwardly and downwardly facing opposite frame parts of the magnetic core structure 40, as seen in Figs. l and 2.

The desired permanent magnetic polarization and unidirectional eld is maintained at the pole pair 42, 52 and the pole pair 44, 54 of the magnetic core, by two elongated permanent magnet members or bars 49 (Figs. 2 and 8) having opposite outer faces held clamped between the overlying inward clamping faces of the two side arms of the opposite pole frame members 45, 55 extending generally parallelto the reed 25, as seen in Figs. 1, 2 and 7, 8, and also in diagrammatic Fig. 4. Each of the two permanent magnet bars 49 is magnetically polarized in a direction perpendicular to the flat surfaces of the overlying pole frame members 45, 55, as indicated by the N and S signs applied to the core bars 49 in Fig. 1, and in the diagrammatic view of Fig. 4.

The armature reed may be pivotally supported in any known manner at its central region so that when vibrated as a microphone part in opposite directions on its central pivot support, the two opposite reed ends 26, 29 will approach one set of opposite- polarity core poles 42, 54 in one half-cycle of each vibration cycle, and will approach the other set of opposite-polarity set of core poles 44, 52 in the opposite half-cyle of each vibration cycle. As the two opposite reed ends 26, 29 so approach in opposite vibration half-cyles, opposite- polarity core poles 42, 54 and 44, 52, respectively, the permanently magnetized core will induce in reed 25 oppositelydirected magnetic fluxes, respectively, indicated by singlehead arrow 25-1 and double-head arrow 25-2 (Figs. 1, 4) and thereby generate corresponding oscillating electric signal currents in the surrounding transducer windings 39. When operating as a receiver, opposite half-cycles of oscillating current traversing the transducer windings 39 will induce in the reed 25foppositely directed magnetic polarizing fluxes indicated by the two opposite arrows 25-1, 25-2. As a result, the two alternately polarized reed ends 26, 29 will vibrate between the respective two sets of opposite- polarity core poles 42, 52 and 44, 54, in `accordance with their alternating polarization.

In the lacoustic transducer shown, one reed end, namely reed end 26, is held clamped and xed by central clamping screw 64 at a magnetic center position between the overlying opposite- polarity poles 42, 52 of the permanently magnetized core, so as to pivotally support the reed 25 for vibration with free reed end 29 in the air gap between opposite-polarity core poles 44, 54 (Figs. l and 2). When operating as a microphone, the acoustic diaphragm drive rod 22 vibrates the reed 25 in spool compartment 32, and the free reed end 29 will alternately approach the opposite- polarity core poles 44, 54 and similarly induce oppositely directed magnetic fluxes indicated by opposite arrows 25- and 252 in successive half-cycles of each complete vibration cycle and thereby generate corresponding oscillating electric signal currents in the surrounding transducer windings. When.

4 operating as a receiver, with the clamped reed end 26 held ixed in the magnetic center between the overlying opposite- polarity core poles 42, 52, oscillating currents traversing the transducer windings 39 will induce in the armature reed 25, oppositely directed magnetic polarizing fluxes indicated by the opposite arrows 25-1, 25-2, thereby causing the free reed end 29 to vibrate in the air gap between its associated opposite- polarity core poles 44, 54 in accordance with sequence of opposite polarizat-ions imparted to the free reed end 29 during each opposite half-cycle of each complete reed vibration cycle.

In the transducer of Fig. 1, the opposite surfaces of theaclamped, xed reed end 26 are held spaced 'from the two opposite-polarity central pole portions 42, 52 of the core structure 40 by spacers or shim's 61`, 62, 63 so as to maintain the clamped pivot reed end 26 in the magnetic spacing center between the overlying opposite- polarity core poles 42, 52. When the transducer windings 39 of such transducer are not traversed by any direct current of the transistor-amplifier circuit, the magnetic spacing center coincides with the physical spacing center, and the clamped reed end 26 is held in the physical spacing center between the opposite- polarity core poles 42, 52 by nonmagnetic spacer shims of non-magnetic metal, for instance, of the same thickness. When the transducer windings 39 of such transducer amplifier hearing aid are traversed not only by alternating signal currents, but also by a direct-current component of the ampliiier circuits, such direct-current component imparts permanent directcurrent polarization to clamped reed end 26, thereby shifting the magnetic spacing center to a point other than the physical spacing center between the overlying oppositepolarity core poles 42, 52. In order to maintain the clamped reed end 26 clamped in the true magnetic spacing center position between its overlying opposite- polarity core poles 42, 52, the clamped reed end 26 is shown held spaced from core -pole 52 by-a non-magnetic spacer shim 62 and a magnetic spacer shim 63, and the opposite side of the clamped reed end 26 is held spaced from the opposite-polarity core pole 42 by a non-magnetic spacer shim 61 of non-magnetic material the thickness of which is chosen to assure that the clamped reed end 26, which is additionally polarized by direct current through the transducer coil 39, is held clamped and retained in a true magnetic spacing center between the opposite- polarity core poles 42, 52.

As indicated in Fig. l, clamping screw 64 has a head overlying the outer surface of the depressed central core pole portion 42 of core arm 41, and it has a threaded rod or shank which passes through corresponding aligned openings of core pole 42, reed end 26 and spacing shims 61, 62, 63, and the threaded opening in similarly de-V pressed central core pole portion 52 provides for proper, positive mounting and clamping engagement of the clamped reed end 26 at the proper magnetic center position between the core polesv 42, 52. The other screws 65 passing through holes in opposite end portions of the other pairs of pole arms 43 and 53 of the two core frame members 45, 46, respectively, complete the clamping ccnnections between the two pole frames 45, S5 across the two elongated permanent magnet bars 49 and join them into a relatively rigid unitary, self-supporting magnetic core structure 40.

The elongated spool member or spool 31 of the transducer windings 39 (Figs. 1-3 and detail Figs. 5 to S-B) has a at cross-section corresponding to the cross-section of the reed 25 which it surrounds. The spool 31 has two iiat spool walls 32 enclosing between them a dat centra spool compartment 33 within which the major part of the reed 25 is positioned for vibratory motion in the spool compartment 33 in a direction transverse or perpendicular to the major surface of the reed and the spool walls 32. The spool 31 has two end walls 34 of a height corresponding to the height Yof the surrounding core structure 4,6, and side edges which have fitting engagement with innamora .inward :side edges 46 `of 'the-,two pole :frame members 45,

55. Referring to Figs. :l-3 ianddetai'l Figs. 7, a8, the two generally rectangular .core frame .members 45., 55 are identical in shape and .in every other respectyandalo'ng its inward edge each core frame member Y45 55 fhas inward 'side-arm edges 46, four corners with corner edges 47,

.frame corner edges 47 whichfextend perpendicularly to f the side frame edges v46,' corresponds to the longitudinal distance between the outer surfaces, 36 of the spool end walls 34 so as to receive with analigning t and posi-l tively locate the end surfaces 36 of the lspool end walls 34 and `positively locate the longitudinal operative position of the spool 31.

- In miniature acoustic signal invention, where space limits are critical', the distance between the spool compartment walls 32 (Fig. S-B) which define the operative compartment height across :which the armature reed 2.5 vibrates, must be vkept to a minimum. Thus, in a miniature transducer operating with a 4magnetic armature reed having a thickness of .010", it is vdesirable to keep the height of the spool compartment 331er the distance between its at Walls 32 to a minimumat which their inwardly facing surfaces will remain free from the slightest interference with the freely vibrating portions of reed 25 held between them. Asfan example, in vthe specie transducer shown, it is ydesirable -to keep `the'distance between the'facing spool walls 32at about .026i.001' The minute dimension tolerance of .001'inthe height dimension of such spool is neededfor-.enabling production of such spoolson a practical basis, as ,by molding with a resin, without prohibitive shrinkage losses.

In assembling the components of such miniature transducer, critical problems are Vencountered in .the proper positioning of the spool 31 in relation to thecore 40, for assuring that the spool compartment walls 32v are at the proper critical distance from the opposite surfaces of the transducers of the present I spool .end :wall 34 is provided along its outward end wall surface '36 with two spaced outwardly projecting spool aligning shoulders or projections 37 extending parallel to the direction of the vibratory motion of the -reed 25. Each of the four spool aligning projections 37 has a pair of accurately positioned transverse spool aligning surfaces 38 which define the height at which the vassembled corev pole frames 45, 55 are engaged by them so as to assure that they are placed in the accurate operative position wherein the central spool compartment walls 32 remain free from interfering engagement with the vibratory reed passing therethrough. The space ing of each pair of spool aligning surfaces 33 is identical with the spacing of the facing upper andlower surfaces of the permanent magnet core bars 49 (as seen in Figs. l

and 3) which are held clamped bet-Ween the two core placed outward portions 'of the-spool structure 31, thereby assuring that the four aligning vshoulders 37 will engage four .peripherally displaced cooperating aligning surfacesat thev four corners of each ofthe two outer core pole`framesv'45, 55, and enable accurate aligned positioning and assembly -gof the core elements 45, 55, 49, the spool 3-1 vand the reed 25 into the composite, operative transducer unit '40 shown. By providing the tiny spool 31 with .the four peripherally displaced aligning shoulders V37 lalong the outward surfaces of the -spool end Walls 34, the assembly and accurate positioning of the -spool with theV other elements of the -composite transducer structure is thus greatly simplified. By Way of example, such assembly may be performed as follows:

In a suitable jig, there is iirst positioned the lower core pole frame 55. Ifter placing on the transverse corel properfpositions with the spool end Walls 34 fitting bevibratory reed 25. Even with skilled operators, excessive production shrinkage is caused byfailures in the required accurate positioning of the spool 31 with respect to the magnetic core 40, that would eliminate interference with `the free reed vibrations inthe assembled transducer, and avoid prohibitive shrinkage losses. K

In accordance with the present invention, the critical difficulties encountered in lthe accurateV positioning of the spool compartment walls 32 relatively to the major surfaces of the vibratory reed 25 when assembling such miniature transducers,v are substantially overcome by providing the spool end walls 34 at a plurality of pc-V ripherally spaced regions thereof with outwardly extendi ing aligning projections` or members of a .height corresponding exactly to the operative spacing of the two opposite pole frame members45, 55, and arranged for aligning engagement with peripherally displaced portions of the assembled core frame members 45, 55. Since the spacing .of the two pole frame members 45, de-

ines the spacing of their two sets of opposite-polarity pole pairs42, 52 and 44, 54 and the magnetically centered operative position of the reed 25, such peripherally displaced aligning projections of the spool 31 make it possible to assure that in the assembly of the transducer components, the two spool compartment walls 32 are automatically positioned in the yrequired critical spacing relation relatively to the vibratory reed Z5 extending therethrough.

Referring to `Figs. 1 3, and detail Figs. 5-5"l3',1each tween .the twoinward side edges'46 and the four 'corner edges 47 of the lower core frame 55. This brings the four downward spool aligning surfaces 3S of the spool 31 (as seen in Figs. l, 2, 5) in Yaligning contact engagement with four peripherally `spaced valigning corners 47 of the lower pole frame 55. 'Thereupon the upperV shim,

such .as shim `61, .is lplaced over the to-be clamped reed .end26 and the two permanent magnet cores 49 are placed along the side arms-of the lower pole frame `member 55 within the assembly jig. Thereafter, the

upper pole frame mem-ber 45 is placed in the jig wherein 1t 1s automatically aligned over the component assembly,

Vin which position the inwardly `facing surfaces of the .four inner corners4'7 of the upper frame 45 automatically come intoaligning engagement with the peripherally dis 'placed upwardly .facing spool aligning-surfaces 38 of the four spool aligning projections 37, thereby automatically assuringthat the spool 31 with its Yclosely spaced compartment walls 32 willbe properly aligned with respace to the two core pole frame members 45, 55 and therethrough with respect to the vibratory transducer reed 25.A The assemblyis completed by screwing in position lthe three clamping screws 64, which 'join the assembly into the operative transducer unit.

The outwardly extending aligning spool projections 37 do vnot increase the over-all dimensions of the transducer assembly because the spool-aligning projections 37 merely occupy space available at the four inner corner regions of the generally rectangular core assembly 40 of the transducer. The aligning spool projections 37 also make it possible to provide the spool body 31 around which the transducer windings are wound, with the required rigidity while reducing to a minimum the lateral vspace occupied bythe Vwalls of the spool compartment 33,as seen'in Figs. l-S and S-B. The reduction of the Jlateral 'space occupied 'by the walls :of the spool compartment 33 of the winding spool 31 is secured by eliminating the side walls of the spool compartment and utilizing as Winding support only the two at spool. compartment walls 32 bordering the upper and lower sides of the minute spool compartment 33, as seen in Figs. land 5B. The required additional rigidity that `would be supplied by compartment side walls, is provided by the four aligning projections 37 which serve as four reinforcing members extending transversely to the two spool compartment side walls 32 and give them the rigidity for providing the proper support for thc transducer windings 39, and assure that the two spool compartment walls 32 are not deformed under strain and are maintained at the correct spacing of the spool compartment 33 free of interfering engagement with vibrating portions of the armature reed 25.

In miniature transducers of the foregoing type, it is desirable to utilize highly permeable ferromagnetic material, for instance the material known as Hymn 80, for the resilient, vibratory reed 25. The limitations on the minimum required cross-section and on the length of the vibratory reed 25, make it diicult to obtain a reed of such highly permeable magnetic material which will op erate with the compliance required for optimum transducer sensitivity. In accordance with the invention, the vibrator-y ferromagnetic reed is given the desired greater compliance within the required minimum length and thickness dimensions, by arranging the clamping connection of the clamped reed end 26 in such manner as to permit free vibration of a part ofthe clamped reed end 26 which would normally be held clamped and restrained against Vibration. The novel arrangement of the clamped reed end 26 which increases the free vibrating length of the reed, while assuring that the clamped reed end is properly maintained in its clamped operative position, will now be described (Figs. 1, 2, 6 and 9).

In the accepted prior-art practice, the spacing shims 61, 62, 63 with which the reed was held clamped between the facing pole portions 42, 52 of the two pole frames 45, 55, l

normally extended over the entire area of the reed end 26, which is embraced by the two pole portions 42, 52, of core frames 45, 55. In accordance with the invention, the dimensions of the spacing shims, and particularly of the non-magnetic shims 61, 62 overlying the clamped reed end 26, are limited along the longitudinal direction of the reed 25 only up to at most three-quarters of the reed area embraced by the core poles 42, 52. In the arrangement shown, the two spacer shims 61, 62 have the shape shown in Fig. 9. Each shim, such as shim 61, has two arms extending from its outer edge along both sides of the fastening member or clamping screw or rod 64 to the inward edge of the screw opening 61-2 through which the clamping screw 64 passes. The so-ormed shims 61, 62

i of the clamped reed end 26 conne the clamping engagement to the outward edge region of the clamped reed end and two rear portions of the adjoining reed mounting portion embracing the clamping screw 64 which are in clamping engagement with the inner edge 61-2 of the adjacent overlying spacing shims 61, 62. In addition, the part of the clamped reed end 26 with the reed opening 26-1 (Fig. 6) through which the screw 64 extends, is enlarged in the adjoining inward reed region extending beyond the overlying inner spacer shim edges 61-2, thereby providing the free inward reed portions adjoining the clamped reed end 26 with two llexible resilient reed junction arms 2543 having a radial dimension shorter than the radial dimension of the adjoining reed portions which are held clamped between the shirns 61, 62. This makes it possible to give the reed 25 the desired greater compliance and secure operation thereof with the desired resonant mode at which the acoustic transducer will operate with desired over-all response.

CII

ing-aid, the connections to the windings 39 are provided by two flexible wire conductor leads 56 which are covered by an insulating coating layer and pass through an opening in a rim side wall of transducer casing 71, with the opening being sealed as by cement so as to retain therein the conductors 56 and keep the lead opening sealed. The internal ends of the two insulated conductor leads 56 are stripped of their insulation and are electrically aixed, as by solder, to two spaced metallic transducer terminals 57, to which the transducer windings 39 are connected. The transducer terminals 57 are mounted on an underlying insulating terminal support which is mounted on the transducer unit 40. The insulating support for the trans- `ducer terminals 57 may be formed of overlapping layers `of insulating sheet material, for instance resin-impregnated cloth, holding between them one leg of two tiny U- shaped terminals 57, leaving one terminal leg 57 exposed for connection to the stripped conductor lead ends 56.

Miniature acoustic transducers of the type decribed herein, usually also have a casing or cup 71 of suitable metal, for instance, brass or aluminum, within which the transducer assembly is mounted. The transducer structure is suitably affixed to the casing 71, for instance, as by placing four drops 73 of cement along spaced peripheral regions of the upwardly facing core frame member 4S where it adjoins the casing side walls 72 (Fig. 3). The casing 71 has side walls or a rim 72 with a rim edge to which the edge of diaphragm 21 is secured, as by cement. The casing 71` may be of magnetic shield material, where it is desired to magnetically shield the electromagnetic elements of the transducer against magnetic interlinkage with disturbing magnetic fields of another similar transducer, for instance, for suppressing magnetic feedback interlinkage between the electromagnetic elements of'a microphone transducer and receiver transducer forming parts of a transistor hearing aid. The casing 71 may be made of a non-magnetic metal, and where a shield enclosure is desired, an outer magnetic shield casing or cup 74 is l placed in contact with and over the interiori housing cup '71. A cover wall 75 of metal, overlying the exterior side of the Vibratory diaphragm 21, has a rim which is'joined, as by cement, to the casing l72. Acoustic excitation of the diaphragm 21 or deliveryof generated sound, may be obtained by providing the casing cover 75 with one or more acoustic openings.

After the internal transducer unit 40 is assembled in th casing 71 and before the diaphragm 2l is affixed thereto and to the casing, the operative position of the vibrator;l reed 25 is checked toassure that it is in the magnetic center between the adjacent poles 42, 52 of thecore structure. Although proper choice of the magnetic shim in ,relation to the magnitude of the direct-current traversing The optimum operating position may be checked by connecting the transducer windings to an instrument, for instance an oscilloscope, and observing the response of the transducer unit 40 over a critical frequency range thereof. In the transducer shown, such setting tool may be applied to the portion of the reed 25 which is exposed in the transducer unit 44) between the inward edge of the corepole pair 42, 52 and the adjacent spool end walls 34, as seen to the Ileft in Figs. l and 3, the tool being applied in the direction oi' one of the arrows 66. `In order to make it possible for such setting tool to be applied to the reed in the direction of arrows 66 while assembled in casing .'71, this casing and also the shielding casing 74, if used,'are

provided'with an opening 712, thereby exposing at' the i propagated from the exteriorspace through sound the setting of the reed is completed, the opening 71-2 may be closed as by applying thereto, as with cement, a cover plate 71-3. v

The acoustic transducer 20, 'which may be almicrof phone, is shown suspended in the interior of thefhea-ringaid casing so as to suppress transmission of vibrations between the transducer and the outer casing 10 and the other similarly suspended acoustic transducer, such as the receiver mounted in the hearing-aid casing' 10.v Such vibration-suppressing suspension may be provided by generally Zshaped suspension members 10-2 of vibrationdamping sheet material, such as elastomer material, having opposite end tongue portions secured to the outer surface portions of the transducer casing 71 and the hearing-aid casing il'respectively, in which it is carried.

The acoustic responses of a transducer of the type described above, are controlled by the acoustic characteristics of the interior transducer compartment 69 bounded by the inner side of diaphragm 21 and casing 71, and of the outer diaphragm compartment 76u bounded by the outer side of diaphragm 21 and the outer casing cover 75. ln the transducer shown, the acoustic connection from the outer diaphragm compartment 76 lto the exterior space E (in the case of a microphonel'or to the ear canal (in the 10,l specic form of transducer shown, the acoustic passage connection 77 from the outer diaphragm compartment 7 6 to theexterior space is dimensioned to provide an acoustic mass impedance which lowers the resonant frequency 'of the transducer system from about 2000 c.p.s. (cycles per second) to 1400 c.p.s. or in general, to a resonant frequency in the range between 1300 c.p.s. and 1500 c.p.s. Such acoustic passage connection to the exterior space maybe readily designed, as by restricting its cross-section over a specied length thereof, for raising its acoustic resistance and` thereby damp the peaked transducer respense at its resonant frequency.

By forming the acoustic passage connection from the' Vouter diaphragm compartment to the exterior space with a recessed casing Wall channel of the transducer casing rim, the sound connection to the surrounding space is provided along a side wall or rim of the transducer casv ing. Such acoustic connection along the relatively short side wall of the transducer casing eliminates the problems encountered in miniature all-in-one hearing aids when making an acoustic connection to the diaphragm compartment openings of an acoustic transducer through an opening in a casing such as casing wall 75 overlying the recessed channel-shaped wall portion 81 of casing rim 72 Y to form the desired sound channel 77 between the outer diaphragm compartment 76 and the exterior space. vA

cover wall opening 83 connectsthe sound channel 77 to the exterior space. The vibratory diaphragm 21 overlying the upper end of the sound channel 77. (as seen in Fig. 1) has an opening 23g-1 through which the channel passage 77 is connected to the diaphragm front compartment 76, thereby completing an acoustic connection from the exterior space to the outer diaphragm compartment space '76. yIn the case of a hearing aid, the channel opening 33 of the sound channel 77` is 'suitablyprconnected either to the exterior space when operating as a microphone for exciting the diaphragm by exterior sound, or to the ear canal of the user for delivering or propagating the'sound generated in the front diaphragm compartment 76 to the ear canal or the user. in vEig. 1, the transducer is shown operating as a microphone which is excited by sound channel 7,7.

The sound channel opening 33 of the sound passage 77 is connected to a' .casing opening 10-1 of the hearing-'aid casing through'a coupling channel 85 (-Fig. 1) for the transmission of sound propagated in the surrounding space through casing opening lil-1, sound passage 86 of coupling channel `85, sound channel opening 83, and through sound channel 77, into the outer diaphragm compartment 76 for exciting the diaphragm 21 and cause it to generate corresponding signals in the transducer windings 39. The coupling channel 8S may be made of elastemer material, and has one end surface sealingly engaging the surface of the casing 10 surroundingcasing opening 104. The opposite end surface of coupling channel S5 sealingly engagesithe facing opening 83 of sound-passage 77 of casing 'rim 72.

The acoustic passage 73 ,formed by the recessed casing wall portion S1 through which the outer transducer diaphragm compartment 76l is connected to the exterior space, is dimensioned so that it provides 'an vacoustic mass 'impedance which lowers theresonant.frequency'of the diaphragm 21.

ln accordancewith a phase of the invention, such inwardly recessed channel-shaped wall portion of the transducer casing, such as transducer casing 71, is utilized in conjunction with an outer cover portion such as cover wall 82 to provide a sound passage of predetermined acoustic characteristics through which one of the transducer compartments is connected either to the exterior space or to another transducer compartment and thereby modify or control the acoustic response of the transducer over a predetermined frequency range. In addition, such acoustic channelpassage or restricted cross-section may be used, for instance, in the manner described in Knauert Patent 2,820,107, for raisingthe frequency response of a microphoneV between 200 and 600 c.p.s. In the transducer shown, the inner transducer compartment 69 has' Va microphone in the low-frequency range, for instance between 400 and 600 c.p.s., or in general, between 200 and 600 c.p.s.

In the transducer shown, the recessed portion of rim side wall`72 of the transducer which forms with casing cover wall 82 the lrecessed sound channel 77, has further recessed channel wall portions 91 and 92 which form with casing cover wall 82 an additional sound passage `93 which connects sound channel 77 tothe interior transducer compartment 619. The recessed wall portion 92 ofthe additional acoustic channel or passagev93 has an acoustic opening 94 below the levelof the diaphragm 2&1, through which the space of additional sound passage-.96

is' acousticallyconnected to the inner transducer corri-A partment `69. The acoustic impedance of the additional channel passage 93 and its opening connection 94 to the inner transducer compartment 69, is designed to have a predetermined impedance which will form in conjunction with the acoustic space of the inner transducer compartment '69 an acoustic system'which resonates, for instance, at 400 or 500 c.p.s. (cycles per second), for thereby raising the yfrequency response of the microphone in this frequency range, in a manner similar to that explained in vided with recessed channels for forming acoustic .pas-

sages connected to an acoustic compartmentof the trans-` ducer for modifying orV controlling the response of the transducer in a vselected part of its frequency range. 1

. The cover wall 82 which forms with the recessed channel-shaped portions of casing rim wall 72, the sound channels 77 and `93, described above, may be of a dimension just suicient to slightly overlap the width 'of the passage, the cover wall portion 82 being secured to the j.

underlying wall portion of the rim wall 72, as by cement or solder. In the arrangement shown, a single cover wall member 82 is secured Vto the recessed channel-shaped wall portions 81, 92, of the casing side wall, for forming therewith the two sound passages 77 and 93. Where the microphone casing 71 is provided with a magnetic shield, cover wall 82 may be formed of ferromagnetic highpermeability material and may form part of the magnetic shield 74 seated over the inner casing wall `811 and forming a magnetic shield enclosure around it.

' By way of example, there are given below, construction data yof a practical embodiment of the invention in the form of a miniature microphone transducer of a hearing aid:

Reed.-Hymu 80 magnetic material; .010 thick; .300 long; .100" wide, with mounting end .135" wide. Diameter of reed opening .021" to .047; width of two reed arms beyond reed opening .037 to .050" depending on desired response.

Cut-015l spacer shim for reed.-Brass; thickness either 0.002; 0.003, 0.0035"; 0.004", depending on desired response. Distance from opening center to rear edge, .040, and to shorter front edge .010.

Permanent magnet cores-Amico 2; .330" long; .070" in height; .067'l width.

Pole arm framed-Alloy of 50% N, 50% Fe; .025" thickness; .080" pole arm width; .055 side arm width; .215" spacing of inner side arm edges; .218 spacing of inner pole arm edges.

Spook-Nylon; .150" total length; .009 thickness; .115 height; .188 width of reed compartment; .009 thickness of compartment side walls; .026" height and .l18 width of reed compartment; .009" thickness of compartment side walls. Y

Spool-aligning projections.--.070 height transverse to reed; .016 projection length and end area width.

Main casing.-.008" wall thickness; .170 inside height;

.436 by .336 inside area;v .021 channel-recess depth, and .042 channel recess width.

Aluminum foil diaphragm- 0005" foil thickness of receiver; .0007 thickness of microphone.

The claims of the present application are directed to a miniature-size electromagnetic transducer device operating with an elongated vibratory magnetic reed, wherein only a portion of the clamped reed extending only to the clamping screw or rod is restrained against motion, thereby providing a vibratory reed of greater length and better output characteristics than would otherwise be possible with a transducer unit of miniature over-all dimensions of the type disclosed herein. Other features of invention disclosed herein constitute the subject-matter of the co-pending applications Serial Nos. 774,437 and 774,438, tiled by W. F; Knauert on November 17, 1958, and assigned to the assignee of the present application.

lt will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in con-y nection with specific exemplications thereof will suggest various other modifications and applications of the same. It is accordingly desired that in constnling the breadth of the appended claims, they shall not be limited to the specic exempliications of the invention described above.

Vl claim:

l. In an electromagnetic acoustic transducer device, an elongated ilat ferromagnetic reed arranged to vibrate transversely to its dat areas between two opposite end positions and having a mounting reed end and a relatively free `'vibratory reed'en'd, ahollow spool member having an elongated interior space of a cross-section slightly `larger than that of thereed in which the major length of said reedis held for vibration therein in 'a direction transverse to the at reed area, transducing windings Asurrounding and held by said spool member, a ferromagnetic core structure comprising two elongated core bodies extending parallel along opposite sides and conning between them said spool member and one pair of ferromagnetic pole-arms extending transversely to and on opposite sides of each of the two flat reed ends between said two elongated core members and forming therewith two substantially closed ferromagnetic core return paths of opposite polarity in the opposite end positions of said reed and thereby causing vibratory motion of said reed to generate corresponding electric oscillations in said windings and vice versa, two spacer shims interposed along opposite surfaces of said mounting reed end, and an integral clamping rod passing through aligned openings in said mounting reed end and in said shims and en gaging and holding the two pole-arms in clamping engagement against the opposite surfaces of the mounting reed end, at least one of said shims having an inward shim region extending towards the -free end which is at a materially smaller distance from the center of said rod than the outer shim region extending toward the adjacent end edge of the mounting reed end for thereby providing a greater free vibratory length for said reed.

2. In a transducer device as claimed in claim l, the inward region of the mounting reed end bordering the reed opening through which said clamping rod passes being connected to its adjoining reed end by two junction arms, the root portions of said two junction arms where they adjoin the adjacent reed end being spaced from each other by a spacing materially larger than the spacing of the reed arm portions bordering said reed opening which are under clamping engagement with the overlying polearm portions.

3. In a transducer device as claimed in claim l, the inward region of the mounting reed end bordering the reed opening through which said clamping rod passes being connected to its adjoining reed end by two junction arms, the root portions of said two junction arms where they adjoin the adjacent reed end being spaced from each other by a spacing that is at least three-halves of the spacing of the reed arm Vportions bordering said reed opening which are under clamping engagement with the overlying pole-arm portions, both of said shims having an inward shim region extending toward the free reed end which is at a materially smaller distance from the center of said rod than the outer shim region extending toward the adjacent end edge of the mounting reed end.

4. In an electromagnetic acoustic transducer device, an elongated flat ferromagnetic reed arranged to vibrate transversely to its at areas betwen two opposite end positions and having a mounting reed end and a relatively free vibratory reed end, a hollow spool member having an elongated interior space of a cross-section Vslightly* larger than that of the reed in which said reed is held for vibration in a direction transverse to the at reed area, transducing windings surrounding and held by said spool member, a ferromagnetic core structure comprising one pair offerromagnetic pole members extending on opposite sides of each of the two at reed ends, means for causing said vibratory reed end to vibrate relatively to said mounting reed end, two spacer shims interposed along opposite surfaces of said mounting reed end and the overlying pole members, and an integral clamping rod passing through aligned openings in said mounting reed end and in said shims and engaging and holding the two pole members in clamping engagement against the opposite surfaces of the mounting reed end, at least one of said shims having an inward shim region extending towards the free reed end which is at a materially smaller distance from the center of said rod than the outer shim region extending toward the adjacent end edge of the mounting reed end for thereby providing a greater free vibratory length fory said reed. Y Y

5. 1n a'transducer device as claimed in claim 4, the

' 13 inward region of the mounting reed end bordering the reed opening through which said clamping rod passes being connected to its adjoining reed end by two kjuncv tion arms, the root portions ofsaid two junction arms Where they adjoin the adjacent reed end being spaced from each other by a spacing materially larger than the spacing of the reed arm portions bordering said reed Vspacing of the reedarm portions bordering saidy reed opening which are under clamping engagement with the overlying pole-arm portions, both of said shims having an inward shim region extending toward the free reed end which is at a materially smaller distance from the center of saidv rod than the outer shim region extending toward the adjacent end edge of the mounting reed end.

7. In a transducer device as claimed in claim 1, each of thel pole arms of said two pairs of pole arms which extend on the same side of said flat reed forming portions of an integral core structure.

8. In a transducer device as claimed in claim 4, each of the pole arms of said two pairs of pole arms which extend on the same side of said tlat reed forming portions of an integral core structure.

No references cited.

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