US1904702A - Sound reproducing apparatus - Google Patents

Description

April 18, 1933.

A A. THOMAS SOUND REPRODUCING APPARATUS Filed Dec. 16, 1926 2 Sheets-Sheet l INVENTOR 7 April 18, 1933.

A. A. THOMAS I SOUND REPRODUCING APPARATUS Filed Dec 16, 1926 2 Sheets-Sheet 2 llllll INVENTOR Patented Apr. 18, 1933 worn: it. THOMAS, or Yonx..n..$r. g

sounn nnrnonucmc gr nt;

Application filed December 16, 1926." seriain b. 155,116.

The present invention is for sound reproducing mechanism of novel construction and improved operation. As will appear later, certain features of this invention are of V 5 special advantage" inelectric phonographs of the portable or table type, although my. invention is not limited to that particular class of machine. One of the characteristic features of my invention comprises a loud speaking diaphragm in the form of an elastic tensioned sheet of thin metal'or other suitable material. When this diaphrgagm is used in pho-,.,

nographs, it is stretched across a large opening in the outer wall ofthe case or cabinet This diaphragm sheet,

In a preferred form of my inventiomgthe diaphragm sheet" is stretched on a frame which'also carries the electro-magnetic driv- I ingunit for the diaphragm. The frame and all parts carried thereby are insertedas a unitary member into the outer opening of the case or cabinet and readily'secured in position from the outside. -The diaphragm sheet is generally of, rectangular shape,

roughly speaking, and the two longer edges are free to permit bodily vibration of prac- 135 tically the entire sheet across the opening.

Therefore, a diaphragm of comparatively smallarea and of a shape fitting into a com pact carrying case is capable of giving a reproduction of greatvolume.

40 When my invention is embodied in a portable phonograph, the carrying case may have straight sides or it may be cylindrical. The diaphragm sheet referred to is of such a nature that it may be made straight to fit into a rectangular case, or it may be curved p v p brake for starting and stopping'the turn table, or a switch if anelectric motor is used,

to conform to a case of cylindrical shape.

So that my invention may be fully understood by those skilled in the art in order to enable them to practice the same, I shall describe two illustrative embodiments there-j of as shown in the accompanying drawings, in which- 1., Fig. l'shows'in perspectivea portable phonograph 'equipped with mynew' loudi broken away forlack of space; i q

Fig; 2 is a perspective view of the-loud speaking diaphragm, certain parts:

speaking mechanism adapted tobe inserted,

"loud speaking diaphragm;

and

the loud speaking. mec

A handle lOseciired to one Side or the cab; V

as aunit into the phonograph case ofFig. 1,,

a portion oftherear housin l being broken 0' I away to show the parts-fwithm; f p Fig. 3 isafragmentary detail'view showing how theloud speaking diaphragm is see cured along one edge;

' Fig. 4 is a plan view of a modification comprising ;a cylindrical case, the motorboard being partly broken away-to show the Fig. 5 isa front View the construction" ewn in Fi n a somewhat larger scale; 7o

Fig. 6 is a detached erspective jyie 'w, of.

anism adapted .to; r be inserted as a unit in' the-cylindrical case" of Figs4 and 5. "f 1' r I shall first describe "the {construction shown in Figs. 1-3. The'entire' phonograph mechanism is mounted in a cabinet indicated as a whole by C, which is of rectangular shape and is constructed of suitable material, such as wood, fiber', sheet'metal,and the like.

inet permits" the" same tobe easily carried about. A lid or Govern. is hinged at '12 along the rear edge ofthe case and held in open position* by any suitab le -means. Above the motorboard 13 rotates a turntable 14, which is mounted onla vertical shaft 15; in" the ,;usual, way." The shaft 15. I is 'suppos'edto be driven by a motor mounted beneath'the motorboa'rd. As phonograph motors, both mechanical and electrical, are well known in the art,h I need not show ordescribe any motor construction'for operating the turntable. There will, of course, beia'f but'I need notfshow'these parts, since they are obvious. On the motorboard 13 isfixed f need n'ot show or describe any'structural 'detally rotatable post 17 provided on top with a horizontal bearing jl8i A reprodu'cer arm 19,, preferably a lighttube, is pivotedat the rear end on the bearing 18, and at its front.

end it carries an eleetricreproducer 20. The horizontal bearingflSl'allows thearln 19 t0 move vertically iandthe swivel post 17 'perunits it ;to.- swing'ghorizontally over a;;rec-

0rd. Any Other practical form of mounting for the reproducer arm 19 n1ay' be employed. 7 If desired; asuitable support 19" may be provided for holding-the reproducer arm 19 V in .idle'or rest position. I The electric repr o-" ducer may be of any approved construetion, eitherlof the microphone type o'r'the" e e roiliasneti Wee Since there wer producers o'fihoth types in the vInarket, 1';

' tails oifireproducer jflo, "which "will therefore be regardedl as, y... practical ionnQQf; ,elect ph m ph wepro f-i The c c t 7 connections from reproducer 20 may; conyen iently led th ough the tuhular afm 19.,

aiidfthieee g he e wp w to these we; t missi n; devi s. m unte leiv t e motorboa'rd. J Aslmy present invention 7 nothing to do with. circuit1cOnnections for V electric pickups in: phonographs', I ;ne'ed notshow. 'or' describef'a-ny details thereof,1'par-.

ticularly v since phonographic.fa nplifying rw ts w nn e oei i t 's uf qient that .ingFig. .l, I have. indicatedhdiagram;

V matically a battery. L and an amplifying.

- tra s rmer I o ted l e spac e e. m 'f' fr oard, and a= Ii aPhef1 1 -:b j regulate the Volume jfof reproduction. f All piartsu of the amplifying system,may" b he d ii the bine b ow t mo o board, or they-ymay bei mounted in asepar ater case. 5 To permit ready access to thebattery 44- for: replacement, the motorboard 5 is proyidejd with aniopening 4.9 closed .by a cover. I 50. .The' battery isremo ed-and replaced through opening 49owithout disturbing any he lq h p 'on sr phis echanism-e The electric parts housed within the Leasing. are bf 'Q 1 ',.P Qp y se fimdi p it n;

I do not consider .it' necessary ,to' showon; describe any: securing fmeanS, sinceflany fi' sh diwm i'khbwih t9 fiX i wp iti n. 'ha y, .ran o mer', sta r p i y si tube,' and so on.

1] Practically the entire a t is e and th ar e r p n phragm, which is thus held under constant V strainer tension in the direction of its 7 length. The upper and lower edges of the. V diaphragm are free soithatathe diaphragm .inay vibrate bodily. In Figs. 1 and 2 there is .axspace'28 to indicate that the top and bottom edgesof diaphragm 21 ;are not connected land are ,free t d-Vibrate; "QTh'e diaphragrn sheet 21'is. rigidly' connected atits V s of:a' franie indicated as a Whole by F, j whichjs preferably" constructed "of light; 's'trong materialg such as aluminurn and the g. liken Qn the rear 's ide of the supporting ffra'rn'e' is inounte'd'a'housing 25, which is V provided with a rectangular: flangej -26 a'r- 1 ranged togfit, against frarneFy as best shown opposite ends-to the :verticalfside bars 24 in: Fig vS ew .27 1" other. fast ning vdevices pass through.aligned holesi28 in phr sing nd M s g 2 Q1 th ra e-1: Av P he b ack 115.2 are. pr v de 11 the supporting frame F, arins r na e in. ey ndr celi'si ppaift 0.- for ni l=whic f ew ing-an, ctromag et 1 pe eti l-y"cenneqted to" he d phra m a... ec r magne i vi g n si l peekms diap rag :are we k ,T e

siderpit'necessary to show or describe the yfi m t kdqfh c ns u e p r 'pfimy e eln onalt; i 1s ifii t tqes y. hat the -dririna it 3 is.r per r moun i1 ,v p p r and c nne ted ed iaph J libr- .yib rating. the sarne in accordance withthe ;InFig. r di atei h 'qnr eqtion I e r'fi e d aph gm and t driving vunit. @The rear .face. of unit. 2311.; is:

ieqllev bi ti neqf repred r 1: e P i 8 i suppese i prev de wane Pair of n ing Posts? 33 in ar a, as; 111 later: be explained. The" e ie of. d iv n unit 1 31 fi snu ly nifl y d'r wl pn b 3 1 ndgis "ri idly-h l ingposition by any practical means. InrFig.

f r esir nsfl du ter ?t cdnn gthe u it.

have shown strip secured Ito the I ba k 3 i ifi 313 as by c ew 35 f Qth Wise. The ends. of stripfi iproject' into-con mama; the circular flange 36 of support. 30, and are secured thereto; screws 37. T lt will he .ob seryed lfrornlligfltthat therear, I wall of housing 25 LfitS snugly v around the cylindrical support-'30 withoutcovering the I reargfiange 36 thereo'fl: sp that the driving unit 31 may be fitted into place after the housing has heenzmounted'on framework jlt will" beclear 'fromylthelpreceding de-f V ser p en afih the a el a d a Pa tscarried; thereby constituteajunitary struc-j ture adaptedito be inserted as a single insinher zin to the front, opening 3 of the phonegraph case. This. permits the' correct adj use; merit of the;--,driying unit 31 ,andiitscone; n on wi I the a dia hragm 2 befo e thestructural details fof' such a un t, part cular frame F is mounted inthe cabinet of the machine. The frame F is secured in the cabinet by screws 38 passing-through holes 39 into a pair of posts or angle-bars 40 fasf.

tened to the side walls of casing O, as'shown' in Fig. 3. Any other practical means may be employed, for mounting the frame and. its parts in the phonograph cabinet. sides of the cabinet extend forwardly at 41 to support one or two 5 doors 42 hinged at 13. 'When the doors 42 are closed, they completely cover the-frame F. The front edge of top lid 11 may be provided with su1tablemeans forholdingthe closed door or doors 42 locked when the lid is closed, as will be understood without additional illustration. The doors 42 are not necessary if the machine is intended forhome use only. and isnot to be carried on trips, but they are useful in protecting the diaphragm against accidental injurywhen the machine is not used. Also, a pair of hinged doors at opposite sides of the diaphragm may be used as panels to direct or deflect sound waves into the desired direction I The loud speaking diaphragm 21 is preferably constructed of aqsingle sheet of resilient material capable of giving goodacoustic. reproduction. Such material may be metallic or non-metallic, and by way of example I may mention aluminum, brass, steel, impregnated linen, paper, celluloid, and the like. The diaphragm. shown in Figs. 1 and 2 consists of a flat rectangular sheet having a length equal to at least twice its width. Although I have shown the corrugations 22 as integral with the body portion of the diaphragm, they may be formed as separate sections secured to the central portion of the diaphragm. .The corrugated portions 22 perform the double function of holding the central acoustic surface of the diaphragm constantly under tension and resiliently supporting the diaphragm in such a waythat it vibrates with substantially equal amplitude over the entire central area. I do not mean to say that the corrugations 22 are necessary in all cases, but they make it easier to hold the diaphragm stretched,

. and at the same time provide an elastic supfrom passing into the dead space below the l motorboard. At the same time, this housing serves to deflect sound waves outwardly through the narrow openings 23 along the The top and bottom edges of the diaphragm. In this way, the full acoustic effect of the diaphragmis impressed upon the outer; air.

the-outer carrying case :0". of the machine 64 to provide a straight hinge edge for the cov er 65, and also aflat'base onwhich toset thevma'chine when necessary. The outer case "may be constructed o-fusheet metal, fiber, or other serviceable material; The cylindrical wallbf casing C 5 is provided with. an opening.66. adapted to be closed by one or two doors 67 hinged f at 68. .The edges of thelopening 66 maybe re-enforced on the inside by strips 69,:Which may be in the form of a one-piece; rectangular-frame bent to conform to the cylindricalwall of the outer case. Across the-opening 66 is stretched a loud speaking diaphragm D car-- In =the construction of Figs. 4, 5 and 6,

C70 is cylindrical, except that it iscut away at ried :by arectangular'frame 70.: As shown; 7

in Figs landxo, diaphragm D consists of a main centralsection'7 1 andja pairof'end sections 72. The central section 71 is curved i to conform to the cylindrical shape of the outer case, and-the'end sections 72 are suitably secured at their edgesitothe frame 70,

as by means of strips 73, which are held in place by screws 74 or otherwise." The up per and 'loweredges d of the diaphragm are free to vibrate and are therefore slightly spaced from the adjacent portions oi'zcase C, as will beseenin iFigg-yo. The loudspeaking diaphragm D is constructedof "a single sheet of resilient material, which may be of metal I or non-metallic, aspreviously mentioned in connection with diaphragm v 21. Theend portions 72 of diaphragm D hold thecentral acoustic section71 under.

constant tension and act as a resilient supits port for the same. In this way the main portion 71 of-the diaphragm vibrates with substantially equal amplitudeoverits entire area. 7 V

The supporting frame 70 also carriesan electromagnetic unit 75 for operating the diaphragm. Any approved form of driving unitmay be usedyas explained in connection with driving unit 31. The sup orting frame 70 is provided with a'pair 0? cross? arms 76. which terminate in an annular-enlargement 77- adaptedto receive the casing of driving unit'75. A set-screw 7 8 or any other practical means holds the unit 75 rigidly in proper position within the annular support" 77. The'driving unit is operatively connected with the diaphragm D, as

by means of a rod79 If the diaphragmD is made oft-magnetic material, or is otherwise provided"with an armature,-no mechanical connection between the driving unit.7 5 and the diaphragm is necessary; It will therefore be understood that the link or rod 79"of Fig. 4; is intended to represent.-

anyoperative, connection, whether mechani-g iio cal 1 or electromagnetic, between I diaphragm frame 69, whereby the fra1f1'e70, andall its parts are insertable into the-cabinet and removable therefrom as: ai unitary 7. structure. The arms 80 andilugs 8 1 allow' closinglof the doors 67. "InQthe-p'articuIar construe: .tion shownin Fig.7 5; the lugs 81 are Visible:

when*-. the doors 67: are closed,=fbut these 7 doors may be sufficiently wide to conceal all. parts ofthefsupporting frame '70.

:[The construction and mounting of the 'electricfreproducer' of Fig.4 may be the ,same-asithose of re'roducer'20 in I ig ;1,

and I-need not therefore repeat that part Jot V the specification. It will be suflicient it I indicatethe; reproducer'mountin'g of Fig.4

with the: samereference numerals asthe; cor-y respondingfpartsin Fig. 1. WhatI have previously said about the amplifying-trans mission connections between reproducer 20 and driving unit 31 of Figs; 1; and 2, may be :regarded as fullyapplicablelto the reproducer and driving unit of Figs.146.; In Fig.1; 4,, I; have indicated in dotted; outline some "of the-electrical'lparts to begus'edin the amplifying system. Thus, thereeis a; battery 85,.1two V amplifying transformers r86 aand twoamplifying-Vacuum tubes-87,

sujchgas would be lused in a two-stage. am-v plification system. Themotorboard 8,8, of

I .case;zO';..may' have liopeningsj 89 over the Elli:

2 tubes; lThese variouselectricalparts" are motorboard,;and access to theme is attained i properly mounted in the space below; the

in any; convenient way, either byY 'haVing openings in the 'motorboard itself, or by 7 means ofdoors in the outer'wallof the case.

Ito-the machine is to be carried about like a piece 0f hand luggage, it is V preferable tohaxz'e access to the electrical parts through openings-in; the-.motorboard so as not to? weaken the carrying case bytoomany open;

ings in'its outer wall. The battery 85, being.

the heaviest partof the equipment, isprefx erably arranged. opposite the carrying. handle'90, so as to be at thebottom of the Case when the later isstood on'its fiat base.

The 'cylindrioal case'C of Figss l -and 5 needLnot-be much larger than a twelve-inch 7 record; The turntable 91: shown-in Fig; v4cv is supposed tobe twelve inches aerossand the record "92 is'aten-inch record; The di',

ameter of the casing needYnot be m'ore thanabout sixteen inches,' a'nd may" even be 'lessl [From what I'have said above,-litwill"be" clearfthat I have providedan electric 'phono graph iof simple constructio nf. compact ar-Q ran-gement r and capable v of ;;=-g'iying out 'Igre'at voluirie without a horns "The loud i speakingjdiap'hragms are soconstructed and 7 arranged as to require no additionalspace; V they'are practically apart of theouter cabinet" wa-ll.' The small box or cabinet that houses the entire apparatus may be placed 7 upon a-table orl chair for-- playing, and when the machine is not use, it' is easily hidden ina closet, or otherwise disposed of in a small space; A phonograph o'fthat kind is particularly-useful inthe apartments of city dwellers where the rooms aresmall and;

space for furniture is scarce; The ,loud-' V speaking diaphragm fll on vD,-if properly V constructed; and operated," will give ajre production 'equal (or at least oomparable) in volume and tone; quality to that oflarge f a cabinet 7 phonographs, which many apart-f {ment dwellers haveto Vforego on account o't lack of space. When in the description and claims I refer tothe diaphragm'beingfree,,

at two otits'Iedges,-"I .mean that it not rigidly attached at-Vthoseedg'es, and I do'not exclude the idea vofusingdamping means at the free edges, as heretofore employed in' freeedged'cone diaphragms." l f 'In'the' broader aspect of my invention,;it

is not necessarythat all the" electrical "parts constituting "the transmission system shall lee-concealed Within the cabinet itself; If the machine is to; be used as a portable phonograplritobe taken on trips, then ofcourse it Will-"beself=contained; but iffthel-instru-I mentis to be, designed as afsocalled table machine, which isforuseinthe homeonly andnot to be carriedabout like apiece of luggage, th some of the ivarious arts of the electric amplifying fsy'stemjfmay be V f V mountedoutside of the machine "cabinet.

'r-llthough I have shown and described ;my

nvention in the 'form 'o'fa ph'onogr'aph, "it' 1s eyidentfthat my new diaphragm may be its used in other types of "sound-reproducing mechanisms.

I do not herein elaim'per se the particular form of curved diaphragm shown inFigs.

4-6, because a tli r hragrrlv of that kind is claimed in my copending application Serial" Number- 141,692',jfiled October 15', 1926;

I claim as my ,inventio'nz 1 1. In sound-reproduclng ap'paratus,acab.-

i ior inet haying anopening 1n anflouterwalha V loudspeaking 'diaphragm'consistin g of a one: piece tensloned ingy fiat fi /the center, d drlvlng' unit in'said cabinet for o ti said diaphragm;

In sound-reproducing apparatus, a cab-j elastic sheet of 'metal' V stretched across said opening and forming efiecta continiiation' of said wall. and a cover forfsaid'openin'g, said tensioned sheet inethaving an openlng in an outer wall, a

lloudspeaking' diaphragm consisting of a substantiallyrectangular thin elastic sheet ostretched across said opening an'd'forming in effect a cover therefor, means for so mounting said diaphragm sheet that two of its opposite edges are unsecured, resilient means at the other two edges of said sheet for constantly holding the central portion thereof in a state of tension, and a driving unit in said cabinet for operating said di aphragm. r 3. In sound-reproducing apparatus, a cabinet having an opening in an outer wall, a frame secured to said cabinet in said opening, a loudspeaking diaphragm consisting of a flexible elastic sheet having end portions secured to said frame so that said diaphragm sheet is stretched across said opening and practically covers the same, said tensioned diaphragm sheet being unattached to said frame between said end portions, and a driving unit carried by said frame for operating said diaphragm, said frame and the parts carried thereby being insertable into and removable from said. opening as a single member.

4. In sound-reproducing apparatus, a cabinet having a substantially rectangular opening of greater length than width, a

loudspeaking diaphragm covering said opening, said diaphragm consisting of a substantially rectangular elastic sheet having its longer edges unsecured for free vibration of the diaphragm, the central portion of said sheet lying in a plane substantially parallel with the plane of said opening and means for operating said diaphragm. I

5. In sound-reproducing apparatus, a

case having a substantially rectangular opening of greater length than width, a frame fitting into said opening fromthe outside case, a loudspeaking diaphragm consist,- ing of a substantially rectangular sheet attached only at its shorter side edges to said frame and unsecured at its upper and lower edges, said rectangular sheet being held under tension and being unattached to said frame between said attached edges, a support car-' ried by said frame at the rear ofsaid diaphragm, and a driving unit mounted on said support for operating said diaphragm, said frame and the parts carried thereby being insertable into said opening asa unitary structure. 7 p

6. In sound-reproducing apparatus, a loudspeaking diaphragm consisting of a substantially rectangular sheet of stiff elastic material provided with corrugated end portions which act like a resilient support.

for the stiff central portion of the sheet and said end portions running substantially parallel with the attached edges of said sheet,

.on said "support: for operating said diaphragm." I a i8. A .1 loudspeaking. diaphragm consisting of a I single elastic sheet having. a rigid 'central "portion and a, pair of transversely cor- -:rugated*end portions of substantially, the same width as" said -centraljportion, and means for supporting said end portions at tion is held .under tension by i end t1on-s. w I

and having means for securing it to said hold the same under constant tension, supporting means engagingthe edges of said corrugated end portions,the corrugations of 7. In sound-reproducing appamtus, a

substantiallyrectangular frame, a? loudspeakingdiaphragm consisting of Q3. rectangular sheet of stiif'elastio-material provided withcorrugated' end portions which act like a resilient support for'the stiff centralportion'of the; sheet and hold-the same under constanttension, means for I attaching the edgesof said end portions to the sides of said frame, the other pair ofvopposite edges of said sheet being freeto permi'tbodily vibration of- 'said central portion, the corrugationsof said end portions; running subst-antially parallel with the attached edges of the sheet, asupportcarried centrally by. said frame,i'and'fa dniving unit mounted rst their outeredges so that said central por- 9. A loud speaking consist ingof a substantially rectangular" elastic I sheethaving a rigid central porti fi a d a j pair of corrugated iend'portions, means-for supportingsaidendportions at their outer 'Fioo I edges so that said central ypj'ortion held under tension by I said {end 3 portions, and means ioperativ-ely i associated with said central portion for actuating fs'aiddiaphragm. 4

10. In sound-reproducing apparatug a? cabinet having an opening in an outer wall,

a loudspeaking diaphragmconsisting of ga tensioned elastic sheet stretched across said opening and forming in efl"ect acontinuae 1 tion-lof said wall and a cover'for' said opening, said elastic sheet being free at two- Y opposite edges and havingtransverselycorrugated end' portions which hold the central portion constantlyunder tension, and means for operating said diaphragm. 7 11. A loud speaking diaphragm consisting of a flat rectangular sheet plaited transversely and supported under tension at two opposite ends only.

12. .A loud speaking diaphragm consisting of a flat rectangular sheet having a length at least twice its width, and means for securing the two shorter edges of said sheet to hold the same tensioned in the direction of its length, said diaphragm being 1 unsecured at the two longer edgesandpro r videdv with corrugations running substan-' the sheet.

tially parallelwith the supported edgesof 13. An acousticdevicecomprising a rec- I-30 Q6 f j v 7 51,904,702

I tanglf lar frame, a, direct actin diaphragm z 'i 7' ,in the form gfa substantially atrectangu; v

lar sheet suppgrtedipn said 'frame,- means. i '7 carried ,byisaidi frame for-operating said" 1,. 1' diaphragm, and means for ,tensioning said leratingim'eans'.

diaphragm n e direction of it s.fllengighv 5 thml SubStantially Varying the normal v 1 distalnce .between'the. diaphragm and its o'pya loudspeaking. idiaphra, cbmprisingfi "a.

v "2 cabinetwhavi'figiziinppeninginianoutr. wall,

:calbinetiha ving an opening inan outer wall,

substantially fiat elastic s ethsupportedat saidlopefiing and forming a cover therefor, 7 i a. V V 1 'means'foroperatingsaid diaphragxmand a I i f -11: 7' f housing arranged backof said diaphragm r 6 r j to prevent soundfl wz tves from uipassingiinto 'the'gdead'spaceiof ,said cabinetz-w-r .l r f 15.? I so mdareprddueing apparatus, 'a'

' I a 'fia't'rectan'gular frame mouhted a t said .2 ing a' c'oveffoisaid opening throughiwhich' 'fiopening;a loudspeaking diaphragm com- 7 V, 7 Q prisi'ngga substantially flat zrelasti'c sheet 'sup- 1 7 V i A V i i :pol ted Unsaid frame,said diaPhragmform T C v E f Lthe spundpaisses diiectl intothe outer a'ir, i 7 j 1 meanscarrid by sgaid mine-for operating isaid diaphragm, and-a housing carried, by

said frame -;ba; ;k of said diaphragm to pre- T 0 {Vent sound aves from passing into the dead a coustiq idevice,cdmprisingmdi met-acting; diaphragm unif oimly tensiond 130 a high degree and having eans, therein pr viding:li gionsE'of'gpecialExtensibility. I i1 7 40 iphi'agmgintermediate its ends. 7

' phragmf having;corrugationsiransvrse to 517. An acoustic;devicicomprising auni -form1y an'dghighly *tensioned diaphragm g y havingregionsjof specialr extensibility, said i regions comprising}cgnrugationsLinsaid dia- 1 18.7.An acoustiqdevlce comprisingaa diaj- Tone ens on thereofi andQstretched to V V :7 V I V N

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