US3502822A - Electromagnetic transducer having means to optimally position an acoustic reed - Google Patents

Description

March 24, 1970 1 STERNFELD EVAL a 3,502,822

ELECTROMAGNETIC 'IRANSDUCER HAVING MEANS To OPTIMALLY POSITION AN ACOUSTIC REED Filed March 23, 1967 5 Sheets-Sheet 1 F1-G'. Z.. fr E. Z

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ELECTROMAGNETIC TRANSDUCER HAVING MEANS TO OPTIMALLY POSITION AN ACOUSTIC REED 5 Sheets-Sheet 2 Filed March 23, 1967 March 24, 1970 J, sTERNr-ELD EVAL 3,502,822

ELECTROMAGNETIC TRANSDUCER HAVING MEANS TO OPTIMALLY l POSITION AN ACOUSTIC REED Filed March 25, 1967 3 Sheets-Sheet 3 67 4/ 42 ZfZ 235 yz# if United States Patent O 3,502,822 ELECTROMAGNETIC TRANSDUCER HAVING MEANS T OPTIMALLY POSITION AN ACOUSTIC REED vJulius Sternfeld, Tarrytown, and Dimitri Sywyk and William F. Knauert, Yonkers, N.Y., assignors to Sonotone Corporation, Elmsford, N.Y., a corporation of New York Filed Mar. 23, 1967, Ser. No. 625,418 Int. Cl. H04r 13/02 U.S. Cl. 179-114 6 Claims ABSTRACT 0F DISCLOSURE A permanent magnetic ux passes through an integrally formed U-shaped pole core having two parallel core legs with a transverse core junction at one end and an air gap at the opposite core end. A vibratory reed passes through a transducing coil and has a free reed end supported in the pole air gap by a transverse reed support sheet. This reed support sheet has two laterally spaced junctions to the exterior rear surface of the transverse core junction so that at least part of an intermediate support-sheet section is free to vibrate with the reed. An opening or recess in the nearby pole core section enables gripping deformation of the intermediate reedsupport-Sheet section and setting of the optimum reed transducing position in the air gap. The vibratory diaphragm is connected to the reed by a drive rod which passes through an opening of the nearby outwardly deformed core leg which is later returned to its parallel leg position.

This invention relates to reed-type subminiature electromagnetic acoustic transducers small enough for use either as a microphone or a receiver within the thin temple of an eyeglass-hearing aid and also for other analogous applications.

As used herein in the specification and claims the expressions electromagnetic and electromagnetism have the meaning defined in the unabridged Websters Third International Dictation'ary, Copyright 1966. Thus, electromagnetic means of, relating to or produced by electromagnetism; and electromagnetism means magnetism developed by current of electricity physical relations between electricity and magnetism (as the development of magnetism by an electric current or the effect of magnets upon currents).

One widely used reed-type electromagnetic acoustic transducer (U.S. Patents 3,076,062, and 3,163,723, German DAS 1,052,458) operate with a U-shaped pole core structure with a permanent-magnet element held across an air gap along each core-leg pole end of the pole structure and forcing a strong unidirectional flux across the pole `air gap and the two core legs. A thin magneticsheet reed of much smaller cross-section than the pole structure is surrounded by a transducing-winding coil, generally within the hollow coil passage, and with one or front free reed end vibrating in the core-pole air gap. The thin reed sheet material has high permeability to alternating magnetic fluxes and must be annealed after each permanent deformation in order to prevent loss of its high alternating flux permeability. To secure optimum transducer eiiciency, the opposite or rear reed end has to be formed with a support sheet portion arranged to enable its permanent mechanical deformation and adjustment and bring the free reed end into an optimum transducing position within the pole air gap.

Heretofore such reed-type acoustic transducers required complicated or delicate reed supports for enabling permanent deformation of the reed support without loss of the required large alternating-huir reed-permeability.

Among the objects of the present invention is such a reed-type subminiature acoustic transducer which simplies the problems connected with mechanical adjustment of the optimum operative position of the alternating tlux carrying reed both in the partially and also in the fully assembled acoustic transducer device without irnpairing the alternating flux permeability of the reed; and simplification of the manufacture of such acoustic transducer having the desired subminiature dimensions.

In accordance with the invention, a permanent-ux carrying an integrally formed generally U-shaped pole core structure has two parallel core legs joined by a transverse core junction at one end and overlapping a pole air gap at the opposite pole ends. A thin coil surrounded alternating-lluX-carrying vibratory reed has a transversely extending support sheet welded with A.C. flux-transmitting joints to the exterior of the transverse core junction. The support sheet has a reed-adjoining support section accessible from the exterior of the pole structure for bending or deformation and setting the free reed end in the optimum transducing position in the core-pole air gap.

In a desirable form of such reed transducers, a permanent magnet member is joined along a large junction surface to each leg-pole end overlying the pole air gap for forcing therethrough the required large permanent magnet ux. Such core-leg end region should have the maximum permanent ux carrying capacity. It is also desirable that the inner end of the drive rod which transmits vibrations between the reed and the diaphragm should have a pivotal motion-transmitting connection to the reed. In such known desirable transducer devices, the inner driving-rod end is made wider than the reed width and is provided with jaws which grippingly embrace and maintain pivotal junctions with the opposite side edges of the engaged reed portion.

Among the objects of the invention is also a reed-type acoustic transducer device which combines maximum efficiency within the desired minimum overall dimensions of the transducer device. In accordance with the invention, the outer pole-structure core leg adjoining the diaphragm has a small opening in its intermediate length portion, which leg opening is smallenough to provide its core-leg with a cross-section passing the required large permanent-magnet flux. The U-'shaped pole structure is originally formed with its outerl core-leg displaced from its normal parallel-leg position by an angle large enough to enable slipping of the inner wider drive rod end into the reed pivotal driving engagement position over the free reed end of the previously formed and annealed pole-structure and reed subassembly. After annealing this core-reed subassembly, the coil is slipped over the reed toward its supported reed portion, the inward wider end of the drive rod is slipped over the free reed end toward its more inward operative position until its narrow outer drive-rod end passes into the core-leg opening. Thereafter, the outer angularly deformed core leg is deformed and returned to the normal inward parallel leg position. The just described invention takes advantage of the fact that known permanent ux passing magnetic materials suitable for such pole structures will retain the required permeability to permanent unidirectional ux even after being subjected to such just described core leg deformations.

These and other objects of the invention will become apparent from the following description of examples thereof in conjunction with the accompanying drawings in which:

FIG. l is a vertical cross-sectional view of such subminiature acoustic transducer of the invention along line 1 1 of FIG. 2;

FIG. 2 is a cross-sectional view of the same transducer along line 2-2 of FiG. 1;

FIG. 3 is a cross-sectional view of the magnetic core system of the same transducer along line 3-3 of FIG. 4 with the upper core ieg displaced from its normal dashdot line position;

FIG. 4 is Ian elevational View of this core system along line 4-4 of FIG. 3;

FIG. 5 is an elevational end view of the cover wall of the same transducer along line 5 5 of FIG. l;

FIG. 6 and FIG. 6A are an exploded view of the transducer when operating as a microphone or a receiver;

FIGS. 7 and 8 are similar to FIG. 1 showing two further examples of acoustic transducer devices of the invention.

FIGS. 1-6 show one practical example of a subminiature electromagnetic acoustic transducer device operating either as a microphone or a receiver and constituting with an associated transistor amplilier a complete subminiature hearing aid iitting entirely within a narrow temple of an eyeglass frame, or for hidden wear behind the ear, or in its entirety within the outer ear cavity of the user. To simplify the disclosure, it will be assumed that the vertically upward side of the transducer device seen in FIG. l is its upper side and that it has a left and right side as seen. However, in the hearing aid it will be positioned in any of a variety of different other positions.

The acoustic transducer in FIGS. l-6 comprises a vibratory acoustic diaphragm 11 which is connected through a drive rod 23 to a thin elongated high-magnetic permeability vibratory reed 31 passing through hollow space 39 or" the surrounding signal-current carrying transducer coil 38. The thin reed 31 forms part of magnetic core system 40 comprising a U-shaped permanent magnetic-iiux carrying core pole structure 41 having two generally iiat core pole legs 42 and 43 extending generally parallel to each other and to the diaphragm 11 and which are integrally formed with a transverse pole core junction 44 of a single core body. he cross-section of the magnetic two core-leg pole structure 41 is many times greater than that of the magnetic reed 31 which has a free reed end 32 held for vibration in a small air gap 51 provided between the pole ends of the U-shaped pole structure 41.

To the relatively large inward faces of the two opposite core pole ends 42-1, 43-1 are suitably aiiixed, as by a strong cement, similarly shaped permanent magnet members 52, 53 having similarly aixed to their inward faces permeable magnetic pole plates 54, 55 which define `and border the air gap 51. The permanent magnets 52, 53 are magnetized in aiding relation, for instance, as indicated by the symbols N and 5, to force a unidirectional permanent iiux serially through the core loop including core structure parts 42, 44 and the air gap portion 51 with the free reed end 32 held therein. The thin highpermeability reed 31 must be held biased with its free reed end 32 in a magnetically neutral position so that in operation it is traversed principally or solely by an alternating flux in signal transducing relation with surrounding coil 38. The thin vibratory reed 31 is formed integrally with a transversely extending rear support sheet 33 which supports the reed 31 with its free reed end 32 in a neutral position within pole air gap 51, in which the reed 31 is traversed principally by alternating magnetic flux when it is set into vibrations relative to the neutrai position. This requires accurate adjustment of the supported rear end of the reed on the rear portion of the pole structure.

In accordance with the invention, the integrally formed two pole-leg structure 41 is given special configuration and combined with a reed 31 having a rear support sheet 33 extending transversely or generally perpendicular to the direction of the major reed length. Furthermore, this transverse reed support sheet 33 has two spaced support sections 34 laterally spaced from centrally positioned reed 31, and these support sections 34 are aiiixled in such central position for permanent iiux passage as by flux weld joints 35 to the exterior of the transverse pole-core junction section 44 so that the central sheet part 36 holds the reed 31 in a magnetically neutral vibratory position within the core system 41 and its pole gap 51. The reed 31 is initiaiiy positioned for welding so as to be centered and parallel to core leg 43. The pole-core junction 44 (FIGS. 3, 4, 6) has cut therefrom a substantial body section leaving therein a large central rear recess or opening 46 wider than the reed 31 and extending over an adjoining portion of the bottom core-pole leg 43. The core recess or opening 46 of the pc-ie core 4i exposes the central downward reed support sheet section 36 to gripping and permanent deformation or bending by an exterior tool for setting the optimum magnetically balanced operative position of the reed 31 and reed end 32 Within the core system 40 and its pole air gap 51.

For the satisfactory operation of such subminiature transducer devices, it is essential that the reed 31 with its reed end 32 be adjusted to a setting in which it is as close as possible to a balanced magnetic position within the air gap of the permanent flux-traversed pole structure and thereby assure to the maximum extent possible that in operation the vibratory reed 31 is traversed principally by alternating magnetic flux. This balanced reed adjustment must be eiected without introducing into the high permeability thin reed 31 any mechanical strains that would materially reduce its required high permeability.

in the transducer system of the invention, such reedbalancing adjustment is readily made by a gripping of the downward edge of the central sheet section 36 of transverse reed support sheet 33 and giving it a minute bend or deformation until the reed 31 with its reed end 32 has been set in the desired magnetic balancing position. It is desirable to make such adjustment after assembling the magnetic core system 40 with its coil 38 supported on the pole structure and the reed end 32 in the narrow air gap 51 and it may also be made after completing the assembly of the acoustic transducer device within its casing `as seen in FIGS. l and 2.

As stated above, the coil 38 is held as by cement connections to the adjacent pole arms 42, 43 in the position shown and it has an interior very narrow coil space 39 just wide enough and high enough to permit the reed portion passing therethrough to vibrate without interference with the adjacent coil portions. The desired minimum air gap 51 between the facing pole plates 54, 55 is secured by aiiixing at both sides or" reed end 32, as seen in FIGS. 2 and 6, two non-magnetic metaliic spacers 57 which are aflixed to the r'acing pole plates 54, 55 in the positions shown by a thin coating of cement such as used for aiiixing the permanent magnets 52, 53 and their pole plates 54, 55 to each other and to the core pole ends 42--1, 43-1.

Although other drive rod connections between the diaphragm 11 and the reed 31 may be used, the device shown has a thin flat drive rod having the shape shown in FIGS.

l-6 made, for instance, of Phosphor bronze, berylliumcopper, epoxy-tiber glass. This drive rod 23 has a thin upper end passing through a thin correspondingly shaped slot of the diaphragm 11 and is secured to the diaphragm in a conventional way as `by a suitable adhering wax junction. The inward end of the drive rod 23 has pivotal engagement with the adjoining portion of the reed 31. To secure high e'iciency, the lower drive rod end 24 has a pivotal connection with the reed edges. In the device shown, the inward rod end has two arms which embrace and pivotally engage the side edges of the adjacent reed portion so that as the reed 31 vibrates the rod arms 24 will maintain a pivotal engagement with the edges of reed 31 and provide a motion transmitting connection between the reed 31 and the diaphragm 11.

After assembling the pole structure 41 with its reed 31, coil 38, drive rod 23, magnets 52, 53, pole plates 54, 55 and gap spacers 57, it is positioned within a metallic cas,-

ing 61 generally conforming in shape to that of the magnetic transducer system 40, but suiciently large to support at its upper edge 63 the rim of the larger diaphragm 11 which is suitably affixed thereto, as by a heretofore used cement. Previously, the not shown insulated conductor leads of the coil 38 have been passed through minute openings of the casing 61 and sealed thereto.

As seen in FIGS. 1-4, the drive rod 23 is longer than the narrow spacing between its inward junction to reed 31 and the overlying pole leg 42 which has an opening surrounding the upper rod portion joined to the diaphragm. The lower rod end 24 is wider than the pole leg opening 42-2 through which the rod 23 has to pass. It would thus be impossible to place or slide the wide inward rod arms 24 on or over the reed 31 and pass the upper rod end through the core leg opening 42-2 when positioning the drive rod 23 on the reed 31.

The invention overcomes these difficulties in the way described below. Initially, the upper core leg 42 (FIGS. 1-4) is angularly displaced by a substantial angle seen in FIG. 3 from its normal parallel dash-line position 42-4 (FIG. 3).

After welding the reed support-section 34 in the centered reed-position to core junction 44, and annealing this subassembly, the coil 38 is slipped leftward over the reed 31 (FIGS. 1 and 2). Thereupon the inward wider end of drive rod 23 is slipped with wider inward rQd arms 24 over the free reed end 32 to an inward reed position such as indicated by dash-line rod 23 in FIG. 3 until the upper rod end reaches upper pole-leg opening 42-2. The drive rod `23 may be tilted on the reed 31 at the reed pivotal engagement of its inward rod arms 24 to a laterally inclined position so that the upper rod arm will reach the leg opening 42-2 even though the reed-support sheet sections 34 have already been aflixed to pole core junction 44. After so placing thed rive rod 23 0n the reed 31 along upper pole leg opening 42-2, the upper leg 42 is brought or returned from the inclined position seen in FIG. 3 to the desired parallel leg position of FIGS. 1 and 2. After the initial shaping, followed by annealing, the known permanent-flux-passing magnetic core materials may readily be subjected to such deformations without impairing their ability to pass the desired large permanent magnetic flux and the much smaller alternating flux. Because of the subminiature size, the leg opening 42-2 should not be too large so as to leave sufiicient adjacent leg cross-section for passing magnetic flux of the required magnitude.

As disclosed above, the proper minimum air gap space 51 is assured by two non-magnetic metallic spacers 57 (FIGS. 1 and 2) which are aflixed to the pole plates 54, 55 along and slightly spaced from both side edges of the reed end 32 (FIGS. 1, 2 and 6). This feature simplifies the assembly of and accurate positioning of all minute elements of the transducer core system 40 in their proper operative spacing positions. This may be done as follows:

The two not yet magnetized magnets 52, 53 with their respective pole plates 54, 55 and their associated two nonmagnetic air gap spacers 57 are affixed in proper positions to each other, as by a strong cement, into a common magnet and air-gap-spacer unit of the shape seen in FIGS. 1 and 2. To the pole-core 41 of the shape shown in FIG- 3, the support sheet 33 of reed 31 has been welded as described above and this core-reed assembly was thereafter annealed. The coil 38 and inward end 24 of drive rod 23 are thereafter slipped over the reed 31 to the positions seen in FIG. 3. Thereafter, the upper core leg is bent toward and slightly beyond its dash-dot line parallelleg position 42-4 of FIG. 3 so that after deformation, its upper core leg 42 will be somewhat closer than parallel to lower leg 43 by a minute angle. Thereupon cement is applied to inward faces of the core leg ends 42-1, 43-1 and the outward junction faces of the separately assembled still unmagnetized permanent-magnet air-gap unit of elements 52, 53, 54, 55, 57-which is thereupon slipped into and secured in its operative position shown between the two core-leg ends as shown in FIGS. 1, 2 and 6. The soassembled core-coil system 40 is thereupon magnetized in a conventional way for imparting to the two permanent magnets the required permanent magnetization. Thereafter the reed 31 is adjusted to its magnetically balanced setting.

The left side wall of the casing 61, as seen in FIGS. 1 and 6 has an opening 64 conforming to the opening 46 in the left lower part of the pole structure 41 for exposing through casing opening 64 the central support sheet section 36 to gripping engagement by a tool from outside the casing 61 and requires deformation or bending thereof for adjusting the -balanced operation position of the reed 31 and its reed end 32 in the pole structure 41 and its air gap 51. After the reed balancing adjustment, the casing opening 64 is sealed, as by a strip 68 of aluminum which is cemented to the adjacent portions of the casing.

To the casing 61 is secured a metallic casing cover wall 65 having side rims 66 overlying and affixed, as by cement, to the engaged casing side walls as seen, for instance, in FIGS. l and 2. The cover wall 65 is solid and forms with the underlying diaphragm 11 a diaphragm compartment 67 into which `sound from the exterior is propagated for exciting diaphragm vibrations in case of a microphone or for transmitting sound to the users ear in case of a receiver. When used as a microphone, the cover rim wall 66 may be provided with a microphone opening 69 such as seen in FIGS. 1, 5 and 6 through which sound from the exterior space is propagated into the diaphragm chamber 67 for exciting corresponding vibrations of the diaphragm 11 and the reed 31. When used as a receiver, the left side rim 66 of the cover wall 65 is provided along its right region, as seen in FIGS. 1 and 5, with a receiver outlet opening 71 for transmitting sound through a sound outlet nozzle 72 having a wider rim 73 which is aflixed and sealed as by strong cement to the facing rim wall section 66 of the cover wall 65 (FIG. 1). When used as a receiver, a flexible narrow tubing is slipped over the outlet nozzle 72 with the opposite tubing end held coupled by a known-type suitably shaped nipple to the ear canal of the user.

As stated above, after completion of the core assembly 40 with its reed 31, coil 38, drive-rod 23 and its still unmagnetized magnets 52, 53 with their pole plates 54, 55 and air-gap spacers 57, the two magnets 52, 53 are permanently rnagnetized. Thereupon, transverse reed sheet portion 36 is adjustably deformed to set the reed 31 in the required magnetically Ibalanced position within pole air-gap 51, so that it may thereafter be mounted within the casing 61, 65 with reed 31 joined by driverod 23 to the diaphragm. The balanced magnetic setting of the reed 31 is determined by any known procedure.

As an example, audio-frequency electric signal cur- ,rerits of predetermined constant amplitude level are passed through coil 38 and the voltage across the coil is observed on an oscilloscope for frequencies including the resonant frequency of the reed 31. In such reed transducing system, the reed vibrations are reflected on the oscilloscope as the motional impedance of the reed coil 38. Good results are obtained by adjusting the reed position through minute bending of central reed-support sheet section 36 until the oscilloscope shows that this motional impedance is a maximum. This adjusted reed condition corresponds to the lowest resonant frequency and maximum compliance of the reed. If the reed is unstable and tends to freeze to one of the air- gap pole plates 54, 55 in such adj-usted reed position, the permanent magnets 52, 53 are slightly demagnetized until the reed freezing is eliminated. There is thus secured the primary magnetically 4balanced setting of the reed 31 within the small air gap 51 of the core system 40.

After assembling the so set reed core transducer system 40, it is assembled with the diaphragm 11 within the casing walls 61, 65 as described above. Thereupon, the

magnetically balanced reed setting in the core air gap is again checked. The left casing bottom opening 64 is aligned with the corresponding pole-structure recess 46 to expose the central reed sheet su-pport section 36 through the casing opening 64. This enables placing a small setting tool through casing opening 64 to check by a similar test procedure the proper balanced setting of reed 31 within air gap 51 and make any required further minute adjustments of the balanced optimum reed setting. After such final reed setting adjustment, the casing opening 64 is sealed by closure sheet 68.

Below are given data of an example of practical construction of an acoustic reed transducer device of the invention described above having overall dimensions of 0.160 x 0.375 x 0.262 inch.

The reed was of what is known as High Mu 80 metal having high permeability for alternating magnetic ilux. It was 0.007 thick, 0.090" wide and 0.275" horizontal length (FIG. l).

The pole structure 41 was of what is known as Allegheny 4750 metal 0.014" thick having good permeability for permanent magnetic flux. It was 0.250 wide, leg length 0.270, leg spacing 0.090".

Each permanent magnet 52, 53 was rectangular with 0.027 thickness and 0.090" by 0.165 side dimensions. Each soft magnetic pole plate 54, S was 0.006 thick.

The coil 38 was 0.130 long, 0.220 wide and 0.087" high and the cross-section of its interior space was 0.100" by 0.022".

To raise their low-frequency sensitivity or response, it is conventional to embody in such subminiature acoustic transducers a Thuras acoustic tubing connection between the diaphragm separated acoustic space 67 and the underlying acoustic casing space in which the electromagnetic transducer assembly 40 is enclosed (FIGS. 1, 2 and 6). For this purpose, the acoustic transducer device of FIGS. 1 to 6 may be provided with a diaphragm mounting or support rim 11-3 as seen in FIG. 6-A underlying the rim region of the vibratory diaphragm 11 and interposed between the rim of the diaphragm 11 and the upper edge 63 of casing side Walls 62.

It is assumed that the diaphragm-support rim 11-3 is part of the exploded view of the transducer device shown in FIG. 6 and is assembled below the rim of the diaphragm 11 into the compl-ete transducer unit of FIGS. l to 4. The diaphragm support rim 11-3 has the required strength and is made of non-magnetic material, such as aluminum or brass of the required thickness. The downward edge face of diaphragm-support rim 11-3 is afxed, as by cement to the upper edge of the casing side walls 62. One corner region of this diaphragm-support rim 11-3, such as its right-forward corner 11-4 seen in FIG. 6-A, extends radially inward under the overlying portion of the diaphragm 11 and has an opening 11-5 within which the upper open end of a known type of Thuras tubing 11-6 is aflixed.

The Thuras tubing 11-6 of a non-magnetic material, such as aluminum or brass, extends into the diaphragmunderlying space of casing 61 and has an open inward tubing end. The downward side of the rim of diaphragm 11 overlying the facing ilat surface of its support rim 11-3 is affixed thereto, as by cement. The right-forward corner portion of the diaphragm 11 is so affixed to the underlying large corner region 11-4 of its support rim 11-3 carrying the Thuras tubing 11-6. Thereafter, the por-tion of the diaphragm 11 overlying the upper Thuras tubing opening 11-5 seen in FIG. 6-A is removed or cut away to provide the desired acoustic passage connection between the upper acoustic diaphragm space 67 and the inward acoustic space of the casing 61 which are separated from each other by the diaphragm 11. The length and cross-section of the acoustic passage connection through the Thuras tubing 11-6 is proportioned in a conventional way in relation to the connected acoustic spaces to secure the desired response increase over the low frequency audio signal range.

Acoustic electromagnetic reed transducers of the invention embodying the new combination of a permanentflux passing U-shaped pole-core with an alternating-flux passing reed characterized by a transverse reed support with the reed setting features described above are also of value when combined with other known drive-rod connections between the diaphragm and reed.

FIG. 7 shows another example of an acoustic electromagnetic reed transducer devices similar to that described above in connection with FIGS. 1 to 2 but having a different known reed-diaphragm driving connection. The reed transducer of FIG. 7 embodies essentially the same elements and features described above in connection with the transducer device of FIGS. 1-6 except for the differences explained below.

It has substantially the same U-shaped pole structure 41 having two parallel core legs 42 and 43 with core leg pole ends 42-1, 43-1 overlapping a pole air gap 51. To the two core pole ends 42-1, 43-1 are secured the faces of the same pole-end spacing unit coupling the two permanent magnets 52, 53 with their pole- face plates 54, 55 and their two air-gap spacers 57. A similar reed 31 has a transverse reed support sheet 33 secured in the same manner to the transverse core junction 44 for adjustably setting the optimum reed-transducing position as in FIGS. 1 4. However, the core structure 41 is originally formed with two generally parallel core legs without the upper core leg 42 initially inclined under an angle to core leg 43 as seen in FIG. 3. The transducer of FIG. 7 operates with a modied known type of drive rod 23-3 having a narrow inward rod end 24-3 which is inserted into its operative position within an opening 31-3 of the vibratory reed 31 for pivotal connection with the adjacent reed portion `by a suitable junction, as by a known cement. The drive rod 23-3 may be formed of a suitable conventional material, such as aluminum, ber glass reinforced epoxy material, or the like. A portion of the drive rod 23-3 adjoining the reed opening 31-3 may be provided with a circular or ball-shaped rod section 23-4 adjoining its reed junction opening 31-3. The drive rod 23-3 may be inserted into its reed junction opening 31-3 through the upper core leg opening 42-2 after the coil 38 has been previously slipped into the position shown along the reed 31. A small quantity of suitable plastic cement may be placed along the circular portion of drive rod section 23-4 adjoining the reed opening 31-3 so as to form an elastic-ally yieldable pivotal junction with the reed portion adjoining the reed opening 31-3. The lower core leg 43 of the embodiment shown in FIG. 7 may also be provided with a leg opening 43-2 aligned with the leg opening 42-2 of the upper core leg. Instead of applying the junction cement to the circular drive rod portion 23-4 above the reed opening 31-3, the junction cement may be applied to the reed opening section 31-3 and the downwardly projecting narrow inward drive rod end 24-3 through the opening 43-2 of the lower core leg 43 as seen in FIG. 7.

FIG. 8 shows a further example of an acoustic reed transducer of the invention. It is in every respect similar to the device of FIGS. l to 6, except for the distinguishing features described below.

It has the identical transducer core system 40-3 with a U-shaped core structure 41 formed with parallel upper and lower core legs 42, 43, such as shown in FIGS. l and '2. The reed 31 has a transverse reed support sheet 33 secured to the transverse core junction 44 in the device of FIGS. 1-6. However, in the device of FIG. 8, the casing 61-5 is somewhat longer in the direction of reed length 31 than that of FIG. l, and the reed 31 has a free reed portion 31-4 which extends slightly beyond the rightward ends of the two core legs 42, 43 seen in FIG. 8. The portion of the upper core leg 42 adjoining the left-side casing wall 62 has aixed thereto a separation or barrier wall 81 extending along the entire width and sealingly secured to the surrounding inner surface of the surrounding casing side wall section 62. The rim of the diaphragm 11 may be of the same dimensions as diaphragm 11 of FIGS. l-6, except that the diaphragm center is aligned with the diaphragm drive rod 23 which is identical with that of FIGS. l to 6 and embraces with pivotal engagement the side edges of the rightward projecting reed end portion 31-4 and connection to diaphragm 11. The rim of the diaphragm 11 may be cemented to edges of casing side wall 68-5 and the rightward edge of the separation wall 81 which is affixed as by cement. Alternatively, the separation wall 81 may be omitted and the periphery of the diaphragm 11 may extend to and be secured to the rim edges of casing side wall 68-5.

The space available in the casing 61-5 under the rightward portion of the diaphragm 11 as seen in FIG. 8 may be used for housing a transistor amplifier 84 with all or most of its components. The transistor amplifier 84 may serve to amplify the output of the microphone coil 38 `and supply it to a similar coil of the receiver. The casing 61-5 may have partition walls for housing in another mechanically isolated compartment a similar transducer assembly or a transducer assembly shown in FIGS. l to 6 and operating in conjunction with the microphone transducer assembly seen in FIG. 8 and its transistor amplifer 84 as a complete miniature hearing aid shaped for wear behind the ear or embodied within the hollow casing space of an eyeglass temple.

What is claimed is:

1. In an electromagnetic reed-type acoustic transducer device,

an acoustic diaphragm maintained for vibratory motion 1n alr,

a generally U-shaped integrally formed pole core structure of magnetic material permeable to permanent and alternating magnetic flux and having two core legs extending generally parallel to said diaphragm with one pole end of each of the two core legs separated by a pole air gap and with the opposite ends of the two core legs joined by a transverse core junction having an exterior core junction-surface,

magnetizing elements held along at least one interior surface of at least one of said leg pole ends and forcing a permanent unidirectional magnetic -tlux across said air gap and through said core legs,

an elongated elastic reed of smaller-cross-section area than said core legs having high permeability to alternating magnetic iux and a vibratory driving connection to said diaphragm,

coil windings surrounding said reed,

said reed being formed at one end in substantially central position with a wider transversely extending support sheet having a flux-transmitting junction to said exterior core junction-surface and carrying the opposite free reed end in optimum transducing vibratory position in said pole air gap,

said wider support sheet having two side regions laterally spaced from said centrally positioned reed, with said side regions having over-lapping portions aixed to exterior regions of said transverse core junction, and with said support sheet having an intermediate deformable sheet section exposed to gripping and permanent deformation from outside said pole structure for adjustably setting said optimum free-reed-end transducing position. 2. In a reed-type acoustic transducer device as claimed in claim 1,

the region of said transverse core junction adjoining said deformable reed-sheet section and more remote from said diaphragm having an aperture exposing said deformable sheet section to gripping and permanent deformation from the exterior of said pole structure for adjustably setting said optimum freereed-end position in said air gap, said magnetizing elements comprising a permanent magnet overlying with one face the inward face of each of said two pole-leg-ends and with the opposite face said air gap and conjointly forcing said permanent ilux through said pole air gap and said pole structure. 3. In a reed-type acoustic transducer device as claimed in claim 2,

each of said magnets and the adjoining core pole-legends having a pole face overlying said air gap with a larger pole-face area than the facing area of the said reed end portion held in said air gap. 4. In a reed-type acoustic transducer device as claimed in claim 2,

said pole structure having a recess in the structure region adjoining said deformable sheet region and said sheet structure being grippingly engageable for desired deformation through said structure recess. 5. In a reed-type acoustic transducer device as claimed in claim 2,

said pole structure having an aperture in the structure region adjoining said deformable sheet region and said sheet structure being grippingly engageable for desired deformation through said structure aperture. `6. In a reed-type acoustic transducer device as claimed in claim 2,

said pole structure having a recess in the pole structure region adjoining said deformable sheet region and said sheet structure being grippingly engageable for deformation through said structure recess, said pole structure having a casing enclosure with a rim carrying the periphery of said diaphragm, said enclosure having a casing aperture exposing said deformable sheet region to said gripping and permanent deformation.

References Cited UNITED STATES PATENTS 3,076,062. 1/ 1963 Fener 179-114 FOREIGN PATENTS 53 1,1431` 8/1931 Germany. 1,119,336 12/ 1961 Germany. 1,146,542 2/1961 Germany.

392,318 3/ 1932 Great Britain. 396,165 8/1933 Great Britain.

KATHLEEN H. CLAFFY, Primary Examiner J. S. BLACK, Assistant Examiner

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