US2371819A - Sound reproducing unit and method for making the same - Google Patents

Description

March 20, 1945 G. E. GUSTAFSON SOUND HEPRODUCI NG UNIT AND METHOD FOR MAKING THE SAME Filed April 23, 1943 Metal mmvrox.

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0 5W A m w rwB m I Patented M. 20, 1945 scum) amonucmd UNIT AND METHOD 1 non MAKING 'rna sum Gilbert E. Gustafson, River Forest, 211., minorto knith Radio corporation, a corporation of Illinois Application'April 2a, 1943, Serial No. 484,153

, 1's Claims. (c1. 179-107) This invention relates to sound reproducing devices and a method for making the same.

In many sound reproducing systems, and especially in hearing aid app ratus, it is essential that the sound reproducing unit be orsmall size, inexpensive and 01' sturdy construction. Here tofore these desiderata were not always attained,

Figure 5 is a sectional view taken substantially ion line !--5 of base II in Figure 6 in the absence because much skill and time were required to provid the correct air gap distance between ac.- tuating magnets and the associated movable diaphragm, because the parts of the system were of small'dimensions, and because there was a large number of parts making up the composite sound reproducing unit.

It is therefore an object of this invention to provide a small, compact, inexpensive and sturdy sound reproducing unit especially suitable for use in hearing aids.

Another object of this invention is to provide a new and improved sound reproducing unit in which there is provided an air gap between actuating magnets and associated diaphragm of ac curate dimension, which gap is maintained fixed with a high degree of stability.

Another object of this invention is to provide a small, compact, sturdy sound reproducing unit having 9, minimum number or parts.

Another object of this invention is to provide a new and improved method for assembling the parts of a sound reproducing unit which lends itself to mass production and yet insures a constant and stable air gap distance between actuating magnets and diaphragm.

This is the parent of a divisional application, filed March 11, 1944, Serial No. 526,094, in which claims are directed particularly to the process ofmaking sound reproducing units described herein.

The features of my invention which I believe to be novel are set forth with particularity in the a pended claims. My invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which:

Figure 1 is an exploded view of one embodiin practicing the method of my invention to pro duce a unit as illustrated in Figure 1;

of pole pieces HA, HA and yoke II. v

Figur 6 is a perspective view showing apparatus for moulding the base of the unit shown in Figure 1, the section through the base being of a partially assembled unit as produced by the cementing process in Fig. 'l;

Figure I is a view partly in elevation and partly in section showing the assembled jig of Figure 4 mounted with the cooperating base member In illustrated in Figure 1 arranged to practice the method of my invention; the sectional part being taken on a line corresponding to lines 1-! ofboth Figs. 4 and 6.

Referring toFigure 1, the sound reproducing, unit comprisesa base It], pole pieces II and i2, permanent magnet yoke i2, magnet coils l4 and ll, terminals l6. and I1, diaphragm l8 and cover l9. v The base I0 is of insulating material, suchfas Bakelite or the like, and has an inner cir'cular ledge 20 upon which the diaphragm l8 normally rests. The base to has also a second lower inner ledge 2| upon which the terminals IE and H are fastened (preferably by means of screws ISA and "A or the like), and still lower oppositely disposed ledges 22 and 23 (see Fig. 6) uponwhich the magnet coils, It and I! rest. The base In has also a centrally located recess 24 in which the pole pieces H and I2 and yoke i3 are snugly received and in which theyare fastened by means to be described later. The base "I hastwo parallelly extending and integrally formed portions 25 and 26 in each of which is a hole adapted to receive a rod shaped electrical contact member (not shown), so that such electrical contact members, when inserted in the portions 25 and 26, make electrical connection with the terminal portions 21 and 28 of terminals I6 and H, which portions 21 and 28 extend through base holes 29 and 30 (see Fig. 6) into the portions 25 and 26 V v of the base Ill.

The base ill, of Bakelite or other similar material capable o1 being molded in suitable form and shape to form the various ledges and re-v cesses and integrally formed projecting portions, is formed between a pair of cooperating dies and il. in Fig. 5, the inner surface 620i die QB being of the same shape as the outside surface 0 base member I B and the outerfsliifi'ace 63 of GI having the same contour as the i" ofbasememberlfl.

In the manufacture of base'memb or similar material is placed in die 0, the die I is then placed in cooperating relationship with die 80 with the Bakelite or similar moldable material therebetween, and the Bakelite is caused to solidify by applying heat thereto in well-known manner, with the result that when the dies II and 6| are separated from each other and 1mm the solid Bakelite, "base member Iii is produced. Terminal holes are then drilled by conventional means in base ortions 25' and 26 for a purpose described later. r

The yoke I3 is of magnetic material, preferably Alnico, an alloy 01' iron, aluminum, nickel and cobaltdn such proportions that the alloy has great permanence and coercive force. It

abuts against and holds the pole pieces H and I2 1 in spaced relationship.

The magnet coils it and I are wound on bob- .bins HA and ISA which have rectangularly shaped hollow cores MB and I53 which maybe pressed over the smaller portions HA and [2A 01' pole pieces H and I2 which extend therethrough.

The diaphragm l8 comprises a thin disk having concentrically mounted thereon a smaller disk IBA sufllcient to increase the central thickness of the diaphragm l8 so that it can carry the magnetic flux from yoke l3 and coils II and I 5 without undesirable saturation.

The cover l9 has a circular shoulder ISA (see Fig. 8) adapted to engage tightly against the inner wall of base In but not or suiiicient vertical extent to bottom against diaphragm l8. It also has an extending tubular projection 19B adapted to receive a. sound transmitting-.element.*- In op-:

eration, the cover I! is substantially stationary and the sound impulses generated by movement oi diaphragm I 8 are transmitted through cover opening I90.

The pole pieces II and I2 and yoke II are cemented in and to the base III by a suitable material such as an alloy as shown in Fig. 3. One

heated, preferably by induction heating (see coil 42 in Fig. '7), and, when the alloy cools, the yoke l3 and pole pieces H and I2 are'held firmly in place in and on the insulating base Hi. The bobbins HA and HA supporting coils II and I! are then pressed onto pole tips' HA and "A, and terminals l6 and I! are then fastened on ledge 2|, preferably by screws or rivets. with the terminal projecting portions 21 and 28 extending into the base portions and 28, whereby electrical contact may be made with them when rod shaped electrical conducting members (not shown)- are inserted into the holes in base portions 25 and 28. The diaphragm I8 is then placed on bas ledge 20 and is held thereon due to the action of the magnetized pole pieces H and I2. The cover I8 is then laced on the base and is frictionally The parts cemented preferably have prepared surfaces thereon so as to increase the area of the cemented surface and so as to provide a finished structure, having increased strength. That is for this purpose. the pole pieces II and I2 are provided with notches B and HE respectively,

the yoke II is provided with surfaces ISA hav-' ing indentations IIB therein, and the base III is provided with indentations IDA therein which may partake of a grooved surface.

In order to make the sound reproducing unit heretofore described in. mass production and with a predetermined constant distance between pole pieces II and I2 and diaphragm i8, the jig shown in Figure 4 is utilized. It is important to realize that in small hearing aid reproducing units the pole pieces II and II are mounted approximately .01 inch below base ledge 20 upon which diaphragm l8 rides; and, the diaphragm and outer pole piece surface must be substantially parallel with their separation tolerance in the order of a few percent.

The jig of Figure 4 comprises a circular base plate ll of such outer diameter as to be trictionally held by the upper inner curved wall of the .basei ll. Shoulder 32 on base plate 3| serves to limit'the movement of base plate 3| into base II. In the exploded view, Figure 4, the rectangular shaped collar 38 is adapted to contain snugly within its hollow portion the wedge 34, the pair of channel shaped wedge members 35 and I, and parts HA and I2A of the pair of pole pieces H and I2.

In order to assemble the parts on the Jig, the

channel shaped wedge members Iii and 36 and parts" HA and HA of pole pieces ii and I! are mounted on the base plate 3| within the rectangular ring 23. with channel shaped wedge memhers I! and 38 in abutting relationship to the 40 downwardly extending portions HA and I2A of a suitable lowmelting point alloy includes bismuth pole pieces II and I2. -Then the screw 40 (Fig. '7),

having wedge shaped head 3|, i drawn against the cooperating channel shaped wedge members 35 and 38 by turning the nut Al. As nut H is tightened on screw Ill wedge shaped head 34 is ing as in Figure 2.

drawn into engagement with cooperating wedge surfaces on channel members 35 and 38, and the resulting outward movement "of channel members 35 and It causes parts IA and HA of pole pieces H and I2 to be firmly held in the encircling rectangular'shaped ring 33. Magnetic yoke I3 is then placed on ring 33 betwen the downwardly extending portions HA and Hit of pole pieces H and i2 its magnetism holding it securely between pole pieces II and I2. v

The assembled jig is of such dimensions that I when it is inserted in the base Ill, containing the elements of the sound reproducing unit (such assembly being shown in Fig. '7), the shoulder 32 abuts the upper ledg 20 of base ll (Fig. 6) with the pole pieces II and I2 and yoke l3 inserted in base recess 2| in predetermined spaced relationship to the base ledge 20 after the alloy material disposed between the base I0 and yoke I3 and pole pieces II and I2 melts.

It is noted that the alloy material initially placed in base In prior to inserting the jig therein is usually in powdered form thus causing shoulder 32 to be separated a small distance from the upper ledge 20 of base l0 when such jig is inserted into the base. But, when and as such powdered alloy melts, shoulder 32 approaches its position on the upper ledge 2|! of base l0 either due to gravity forces acting on the composite jig due to other torces applied between base Ill and the lie. Ultimately shoulder" rests on the upper ledge 20 of base II and is held in that position when and asthe alloy later solidifies due to gravity iorces, acting on the-composite jig or due to an external force applied between i the Jig and base member ll.

When high frequency current is applied to the coil .42. (Fig. 7) the low melting point alloy material (or another suitable material), which was initially placed in base member ll around pole pieces II and I2 and yoke it. melts. Then, as the alloy material cools and solidifies after coil 42 is deenergized, the alloy material expands slightly while shoulder 32 is firmly held on the upper ledge 2| of base member l and when the alloy material solidifies entirely, it firmly holds the pole pieces II and I2 and yoke I! to the base II with the races of pole pieces H and II in a predetermined spaced relationship with respect to the -'base ledge 20 upon which the diaphragm I8 is subsequently placed. It is also noted that when the expansible metal .alloy is heated by high frequency currents fiowing in coil 42, eddy currents flowing in such expansible metal produce a magnetic shielding eii'ect on pole pieces I I and I2 and magnetic yoke l3 whereby less heat is generated in pole pieces II stud l2 and yoke ll due to high frequency currents in coil 42 than that produced when the expansible metal is absent. This fe ire is of particul'ar importance since the magnetic state of pole pieces H and I2 and yoke I3 is disturbed much less when eddy currents flow in the expansible metal than is the case when such-expansible metal is absent. After the pole pieces H and I land yoke I 3 are thus cemented to the base l0, they are disengaged from the jig by loosening nut 4| on screw ll.

In the, preferred embodiment of this invention, the P01 pieces are cemented to the insulating frequency induction heating apparatus. It is also apparent that the alloy material may be heated by means other than by the preferred use of electrical induction heating apparatus and base Ill by alloy material which is heated by highasvae a of the pole pieces II and I2 with respect to base ledge 2|. It is noted that since the base recess 24' snugly receives the pole pieces II and I2 and Yoke II. a small clearance exists between the walls defining recess 24 through which the material may pass with appreciable resistance'as it solidifies and consequently a relativelylarge force is. exerted by the expanding material between base l. and pole pieces II and I2. This expanding force is utilized in accordance with the present invention to avoid voids and to establish an accurate air gap distance.

in the insulating base.

In the assembled jig the parts HA and I2A of pole pieces "and I2 abut the base plate 3i and are of predetermined height, so as to assure their correct spacing in the fabricated sound reproducing device, the height of shoulder 32 on base plate ll of the jig beingjust right to assure such correct spacing. V I

The cementing process described herein is accomplished by making use of the adhesive or binding properties of materials which set in cem'enting relation between the parts toi be cemented whereby those parts can be placed in predetermined space relationship, as in a jig, and held in such relation when the cement sets. The cementing process is preferably carried out by using a low melting point material having the property of expanding as it cools, and in which the material adheres to the Furthermore, it is noted that since pressure is applied to the expansible alloy when and as it solidifies it is reasonable to believe that such alloy is in a somewhat stressed condition after the complete solidification process.

While I have shown and described particular embodlments'oi my invention. it will beobvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects, and I, therethis invention is not necessarily limited to they preferred heating apparatus.

The fact that the preferred alloy material has a low melting point,-is metallic and expands as it solidifies makes it a desirable cementing agent in this application. The fact that the material is metallic in nature allows the use of induction heating apparatus and the surrounding parts necessary to place a sufllcient quantity of such alloy material between the base ill and pole pieces I I and I2 in the assembling operations, such sufiicient quantity being of a thickness greater than the thickness present in the finished product, heating such material above its melting point and constraining the flow of such material to a degree as it solidifies such that the pole pieces II and I 2 are firmly pressed and tend to move outwardly against the force of gravity or other external forces which act to maintain shoulder 32 in abutting relationship to the upper edge of 1 base l0, thus assuring predetermined spacing tore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit andscope of my invention.

I claim l 1. In a sound reproducingunit, a base member of insulating material, and a pole piece fixedly mounted on said base in predetermined spaced relationship thereto by metallic cement having the property of expanding as it solidifies.

2'. In a sound reproducing unit, a base member of insulating material having a ledge, and a pole piece fixedly mounted by cement on said base in predetermined spacedgelationship to said ledge. said cement being a-metal having the property of expanding as it solidifies.

3. In a' sound reproducing unit, a base memher having a recess and a ledge, a pair of pole pieces, a magnetic yoke abutting against said pole pieces and holding said pole pieces in spaced relationship, said pole pieces and yoke being disposed in said recess and fixedly mounted by cementon the base member with the faces of said .pole pieces lying in predetermined spaced relationship to the ledge, said cement being of metal having th property of expanding as it solidifies.

4; In a sound reproducing unit, a base member of insulating material having a circular ledge and a recessed portion, a pair of pole pieces. a magnetieyoke' abutting against said pole pieces, said recess being arranged to snugly receive said pole pieces and yoke, a magnetic coil for each One 'of said pole pieces. said base member having a pair of oppositely disposed ledges each supporting one of the magnet'coils, a thin layer of metal parts being cemented I v metal cement having low portions, a

net coils, said base member having a pair of opcement having the property ofcxpa'nding as it solidifies in said recess between said pole pieces,

yoke andbase member, said layer of metal ce-- pair of oppositely d po ed led es and each supporting one of the magnet coils, a thin layer of the property of expanding as it solidifies in said recess and disposed between said pole pieces, yoke and magnet coils and providing the sole means for fastening the pole pieces in predetermined spaced relationship to the first mentioned ledge, said metal cement being of predetermined thickness for accurately spacing said pole pieces insaid base, said base member having a pair of parallel extending holterminal for each one of the magpositely disposed ledges each adapted to support one of the terminal members, said base member having a channel extending from each of the last mentioned ledges to each one of'the hollow por-.

tions, and said terminals each having a projection extending through each channel and into the corresponding base hollow portion.

.6. In a sound reproducing unit, a base member having a recess, a pair of pole pieces, a magnetic yoke abutting said pole pieces and holding said pole pieces in spaced relationship, said pole pieces and yoke disposed in said recess and fixedly mounted by cement on the base member in preagainst said polepieces, ranged to' snugly receive said 10. In a sound reproducing unit. a base member of insulating material, a pole piece in said base in predetermined spaced relationship therein, a thin layer of metal cement having the property of expanding as it solidifies and in a stressed condition disposed between the (pole piece and base and providing the sole means for fastening the pole piece to the-base, said metal cementbeing of predetermined thickness for accurately spacing said pole piece in said base, said thin layer of metal cement being heatable by induction.-heating to its melting point, I

11. Ina sound reproducing unit, a base member of insulating material having a ledge, a pole piece in predetermined spaced relationship to said ledge, a thin layer of metal cement having the property of expanding as it solidifies disposed.

between the pole piece and base and providing the sole means for fastening the pole piece to the base in predetermined spaced relationship to said ledge, said metal cement being heatable to l 7 its melting point by induction heating and said metal cement being so disposed that eddy currents flowing therein when inductively heated reduce the heating of said p'ole piece, said cement being of predetermined thickness for accurately spacing said pole piece with respect to said ledge.

determined spaced relationship in said base, said cement being a metaLhaving the property of ex panding as it solidifies.

7. In a sound reproducing unit, a base mem-.

her having a recess, a pair of pole pieces, a magnetic yoke abutting against said pole pieces and holding said pole pieces in spaced relationship,

said pole pieces and yoke being fixedly mounted by cement in said recess, .and said pole pieces, yoke and base member having cooperating surfaces thereon adapted 'to readily hold said ce ment, said cement being a metal having the property of expanding as it solidifies.

8. In a sound reproducing unit, a base member of insulating material, a pole piece in said base in predetermined spaced relationship therein, a thin layer of metal cement having the property of expanding as it solidifies and in a stressed condition disposed between the pole piece and base and providing the sole means for fastening the pole piece to the base, said metal cement be ing of predetermined thickness for accurately spacing said pole piece in said base.

9. In a sound reproducing unit, a base member of insulating material having a, ledge, a pole piece in predetermined spaced relationship to said ledge, a thin layer of metal cement having the property of expanding as it solidifies disposed.

between the pole piece and base and providing the sole means for fastening the pole piece to the base in predetermined spaced relationship to said ledge, said metal cement being heatable to its melting point by induction heating and 12. In a sound reproducing unit, a base member of insulating material, a pole piece in'said base in predetermined spaced relationship there' in, a thin layer of metal cement having. the property ofexpanding as it solidifies and in a stressed condition disposed between the pole piece and base and providing the sole means for fastening the pole piece to the base, said metal cement be-' ing of predetermined thickness for accurately spacing said pole piece in said base; said thin layer of metal cement being heatable by induction heating to its melting point, said metal cement-being so disposed that eddy currents flow-' ing in said cement when heated produce a substantial magnetic shielding effect on .said' pole piece whereby the heating of said pole piece is reduced substantially when said'metal cement is inductively heated.

13. In a sound'reproducing unit, a base'mem- I per, a pole piece, and metallic cementing material therebetween having the property of expanding asit solidifies to assure a correct spacing of said pole piece with respect to a point on said base. ,1

14. In combination, in a'sound reproducing vunit, a base member, a pole piece, means for producing variable flux in said pole piece, a diaphragm actuated in response to said flux variations and .carried by said base member, and means including metallic cementing material having the property of expanding as it solidifies interposed between said pole piece and diaphragm carrying member to assure a correct spacing of said pole piece with respect to a point on said being of predetermined thickness for accurately spacing said pole piece with respect to said ledge.

15. A sound reproducing unit comprising resillent means composed at least in part of magnetic material for actuating the air to produce sound waves, electromagnetic means responsive to elec trlc currents of voice frequency for producing a magnetic field to drive said resilient means, a

base member supporting said resilient means and unit adiacent thereto being shaped so as to be locked together against relative movement when said alloy is in a solid condition, thereby to maintain said predetermined space relationship.

16. A sound reproducing unit comprising resilient means composed at least in part of magnetic material for actuating the air to produce sound waves, electromagnetic means responsive to electric currents of voice frequency for producing a magnetic field to drive said resilient means, a base member of insulating material supporting said resilient and electromagnetic means,

electromagnetically shielded thereby from heating when said spacer is inductively-heated.

GILBERT E. GUSTAFSON.

CERTIFICATE OF CORRECTION;

Patent No 2 571 819.

It is hereby certified that error appears in the. printed specification of the above numbered patent requiring correction as follows: Page 1, second column, lines 14. to 6 inclus ive", strike out "showing apparatus for moulding the'ba se of the unit shown in Figure 1, the section through the base being" and insert the same after "view" in line 1, same pageand column, and

.that the said Letters Patent should be read with this correction therein that the same-may conform to the record of the case in the Patent Office.

March 20, 1914.5.-

GILBERT E GUSTAFSON.

Signed and sealed this 19th day or June, A. 12.1915.

(Seal) Leslie Frazer Acting Commissionerof Patents.

locked together against relative movement when said alloy is in a solid condition, thereby to maintain said predetermined space relationship.

16. A sound reproducing unit comprising resilient means composed at least in part of magnetic material for actuating the air to produce sound waves, electromagnetic means responsive to electric currents of voice frequency for producing a magnetic field to drive said resilient means, a base member of insulating material supporting said resilient and electromagnetic means,

electromagnetically shielded thereby from heating when said spacer is inductively-heated.

GILBERT E. GUSTAFSON.

CERTIFICATE OF CORRECTION;

Patent No 2 571 819.

It is hereby certified that error appears in the. printed specification of the above numbered patent requiring correction as follows: Page 1, second column, lines 14. to 6 inclus ive", strike out "showing apparatus for moulding the'ba se of the unit shown in Figure 1, the section through the base being" and insert the same after "view" in line 1, same pageand column, and

.that the said Letters Patent should be read with this correction therein that the same-may conform to the record of the case in the Patent Office.

March 20, 1914.5.-

GILBERT E GUSTAFSON.

Signed and sealed this 19th day or June, A. 12.1915.

(Seal) Leslie Frazer Acting Commissionerof Patents.

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