US1767657A - Capacity reproducer - Google Patents

Description

GAPAC ITY REPRODUCER 'Filed Aug. 9, v1929 2 sheets-sheet 1 June 24, 1930 P. E. EDELMAN 1,767,657

CAPACITY REPRDUCER' Filed Aug. 9, 1929 Igwe' UM 242;

v 25 4 5 l v "f2 2 Sheets-Sheet 2 Patented .lune 24, 1930 "UNITED isTATs 'PATeNTyoFr-:ICE

PHILIr n.' EDELMAN, or Cuidado, ILLINOIS, Assreiroa'ro EPH'RAIM BANNING. or

f v cmcAGd'ILLINorsg i' Y CAPACITY REPRODUCER Y Application led `August 9,

,I My present invention relates to capacity reproducers, and is` in part a continuation of my applicationV for Letters' Patent of the' United States, Serial No. 352,201, filed April An object of the invention is' to increase the frequency response and amplitude'revsponse of reproducers of this class, while at the same time eliminating objectionable fuzzy or back-lash rustle sounds comn mon to previously known apparatus of this type when operated at maximum volume of response.

Various other objects will presently appear, and the novel features are more particularly pointed out in the appended claims.

.Various vchanges may be made within the spiritof the invention, as defined by the appended claims. y

A capacity reprducer of this type is generally adaptable to any use to which'apparatus of this class' is suitable, such for example, as for operation on the output of a lradio set, a phonographic apparatus, a public Aaddress system, or reversely for sound pick-up service.

By a series of elaborate tests I have discovered that back-lash sounds previously common to such apparatus when operated .near maximum response limits mayv be eliminated by a newdeparture in thisart, namel ly, the introduction of flexible threads to controll the relative space positions of the operative members of the repro'ducer. Gren-A erically, the invention consists in 'placing flexible back-lash preventing .means intermediate lthe operative reproducer members, and more specifically, and preferably, the use of fibrous thread'relativelyv loosely disposed between said members. Thereby the surprisingly new and useful result sought is attained in that the identical operative members of the reproducer, which would otherwise emit back-lash or fuzzy sounds when the reproducer isl operated near its maximum limits, will, when reassembled with the aforesaid thread means therebetween, reproduce. pure tones at maximum` amplitude free lfrom back-lash sounds.

1929. Serial No.A 384,739..

lrelatively low efliciency in order to-keep below the critical input values of impressed electrical energy, which are suliicient to set up'the aforesaid back-lash effect.l

I am illustrating a preferred form of my y invention in detail by -way of exelnplilica` tion of a suitable practical structure therefor typical of a class of equivalent structurescommon to and within the spirit of the aforesaid invention.

Reference is made to the accompanying drawings', in vwhichy Figure 1 is a-perspective view, partially broken away for illustrative purposes to disclose the relation of the working parts ofa reproducer embodying my invention y Fig. 2 is a suitable diagram of an operl ating electrical circuit therefor;

Fig. 3 lis-a diagrammatic sectioned representation explanatoryof the most probable theory of operation afforded by the invention; and Fig. 4f is a sectioned view showing the relation of frames 5 andll of Fig. 1.

The essential elements of areproducer of this type are firstly, a dielectric'diaphragm 1 carrying and supporting an electrically conductive coating or electrode 2; secondly, a co-operating air permeable electrode 3 disposed `closely adjacent thereto; and thirdly, -V

means to control against back-lash effect, preferably threads 4 sandwiched between said dielectric diaphragm 1 and the air permeable electrode 3.

The dielectric diaphragm The dielectric diaphragm 1 mayappropriately be made in any desired size having an area of preferably at least 250 square inches of any desired shape, rectangular or more. The dielectric diaphragm member 1y is preferably made from a fieXible fabric, such as empire cloth or varnished or dielectric impregnated silk or linen or cotton cloth. Silk empire cloth of commerce, for example, in thickness of at least .008 inch, and preferably not more than .006 inch, is a suitable material for the purpose when supported on a frame 5. So is blaek empire cloth of commerce containing asphaltum of at least .004C inch, and not more Vthan .0055 inch thickness satisfactory, for example, for said material. Any other equivalent material of like general properties may be used.

Essential qualities of the material used for the diaphragm 1 are fieXibility, good mechanical and dielectric strength, stabilized chemical composition of long life immune to decomposition effects of oxygen, atmosphere, and particularly of ozone naturally present in the operation of the diaphragm l; high electrical disruptive strength, 4preferably not less than 900 volts, high dielectric constant, preferably not less than 3 as compared to air, and good elasticity, as well as sci'` pliable texture. The diaphragm 1 is preferably stretched at moderate tension of the support member 5. One surface of the membrane 1 is preferably dusted or coated with a non-conducting powder 6, such as mica dust or finely divided talcum powder to minimize the mechanical friction and adhesion property thereof in service by providing a non-sticky surface afforded by said dust 6. This dust surface 6 is normally held by the `natural adhesion effect of the material of diaphragm 1, or by means of a thin coating of varnish thereon, and is of very minute thickness, preferably of the order of value of such a small magnitude as only .00005 inch.

The other'surface of Amembrane 1 is prefera-bly first coated with a thin even layer of insulating varnish 7 such as vgold japan varnish' of commerce, by means of which the thin'fleXible electrode coating 2 is held and supported on diaphragm 1. The preferred mode of applying the electrode coating 2 is tioroll or brush thin aluminum foil 2 on the varnished surface 7 of diaphragm 1 while said varnish 7 is in the process of drying, and of very sticky'or adhesive consistency. The aluminum foil 2 may be of thickness preferably not over .0001 inch, and the variety sold in commerce of less thickness than this and supported for-handling purposes by a paper layer is suitable. A metal foil ribbon 8 is similarly cemented to aluminum foil 2 by varnish 8 and serves as a contact terminal for electrode coating 2 to permit application of electrical potential to the entire surface of electrode 2.

Vcause diaphragm 1 to emit a musicaldrum sound when tap ed vigorouslyvby a work mans finger. Slince material specified for diaphragm 1 is naturallywaterproof and normally oxidized in the process of its manufacture,4it tends to retain its elastic and shape properties indefinitely, and so far as is known, permanently. Also the electrical characteristics of the material specified for diaphragm 1 are known to be of reliable stability and permanence. Should, by chance,

a slight imperfection originally exist in the impregnated cloth 1,`the varnish 7 tends to repair the defect. If said repair is insuf ficlent, however, the operating potential applied thereto in service will merely transiently puncture at the defective spot and burn .away a small hole in the foil coating 2 sufficient to clear the defect. Since this hole becomes visible, the break may be repaired by scraping away a smallamount of the foil surface 2 adjacent to the ruptured spot, and revarnishing same, after which, if desired, a patch of foil may be appliedv to cover the repair. Normally the specified material never punctures in service, as there is a large margin or safety factor between the rated dielectric strength and the largest normally applied peak voltage to which the material of diaphragm 1 is ever subjected'in service.'

lNhen desired the foil 2 `may ybe subsequently coated with varnish or any other suitabley protective or decorative or utility surface 9, such as paint which is non-conducting, or coated fieXible or crepe paper or'fabric 9, or this element 9 may be omitted asv it does not affect the electrical operation -of diaphragm 1. A i

When desired, the diaelectric diaphragm- 1 coated as aforesaid may be allowed to preferably not exceeding 200 F., If the foil 2 1s employed in the variety sold in commerce with numerous perforations or small memes? to diaphraglm- 1, further assistfin the (more rapid dryin'g'lof'the adhesivevarnish 7.

The div-permeable alaaf/rode While theair `permeable electrode 3 mayf be supported on'the same frame 5 as is used vfor holding diaphragm 1 inthe manner disclosed in my aforesaid application 'for Letters Patent vof the United States, SerialNo. 352,201, filed April 3, 1929, I prefer to employ another frame member 11 for the purpose. Frame 11 may then bemounted in .operative relation with respect to 'frame 5,

vperiod of vibration response of frame 5 and the elements it directly carries. The possibility of undesired frame resonance effects in service is thereby obviated. While, as

shown, a vsingle frame 11 suffices' vfor supportin' the air permeable member 3 in the case of a capacity reproducer of moderate size, for example, of the order of magnitude not exceeding 1000 square inches of area,

I prefer to employ a plurality of such frames as 11 as illustrated in my application for Letters Patent of the United States, Serial No. 356,894, filed April 22, 1929, in the case of lvery large magnitude capacity reproducers for theatre and like'use which may have a working area as great as 400 square feet or more.

Inasmuch as the exact sizeof the supporting frames, such as supports 5 and 11 respectively, as wellas the shape thereof, does not appear' to materially 'affect the response characteristics of the reproducer other thanv to somewhatextend the amplitude of low frequency response of the reproducerl as the size is increased, persons skilled i-n this art have obvious wide limits in design and shape, as well as structural dimensions and materials suitablefor the supports 5 and 11. Kiln dried wood is a suitable vmaterial for the frame supports 5 and 11 and any suitable/fastening means, such, for example, as tacks 14 may be used to attach the elements respectively carried thereby.

lVhile it is permissible to omit element 1.5, presently to be described, the same is 'preferably used for ymanufacturing convenience, as well asto impart a sound controlling effect on the air permeable electrode 3. Any porous or air permeable fabric having fiexibility and elasticity, such as ordinary muslin of good quality, is suitable for element 15, and this fabric is stretched tightly.v on supporting-"f frame 11. AIn theY case' of a frane 11 of large dimensions, a

. stron er. fabric, such as: linen crash, maybe used orfmember 15.- f

Also over frame l1 there is supported and stretched with 'considerable initial tension la woven metal cloth or screen 16. The material used for element 16 may be ordinary tinsel cloth of commerce ofl either straight tinselor crinkled tinsel lame variety, andv preferably purchased with linen instead of cotton supporting threads therefor, or it .may be vfinely Woven metal screen prepared preferably from soft cpper wires in mesh in the range 60 mesh to 150 mesh, either plainly meshed or in dutchweave type with spaced heavier wires interposed in the weave in one direction, as set forth in my application for Letters Patent of the United States, Serial No. 355,957, filed April 17, 1929. In any case, it is essentialA that this metal cloth or Woven material be flexible and relatively thin,'such, for example, within the range of thickness of .002 to .015.

100 mesh of commerce been found satisfactory. Also a Woven wire screen of 60 mesh having interposed wires of thickness in the rangey 150% to 200% of the thicknessof the -vmain portion of suchI screen material at intervals of 3/4 to 11/2,in one direction along the area of such material, has been found satisfactory for the purpose.

In general, the thinner metal cloth or .screen material is more suited to frames `11 of moderate dimensions up to an area of about 4 square feet, while woven metal material for the element 16 may perinissably be of heavier material in the range preferred as aforesaid in the case of a fralne 11, of larger magnitude having an area, sayof 5 to 25 square feet. yIt `is'desirable in Tinsel cloth of commerce vhas,been found' suitable for VYj the purpose. ,So has copper wire screen of.

any case to have the material or woven metal 16,evenly and smoothly stretched on frame 11 without wrinkles.

The elements 17 nextv and presently to lli) be described mayy permissibly be, omitted, i

more particularly in the case where a screen material 16 is employed in which heavier wires are interwoven at intervals therein as aforestated is used. But even in such case, theresult is better 'when the elements 17 are employed, and in this event said elements 17 are preferably cemented directly oven the aforesaid heavier spaced wires of the said i screen material 16. l

The elements 17 consist preferably of thin soft metal ribbons, or.relatively thick metal foil, such as lead or tinfoil, of thickness within the range .001 to .003, and width within the range 1A, to 1/2. A lead foil ribbon l3/8 wide and .0015 thick has been found suitable. Also in some instances it is desirable to employ material for elements 17 of varying thicknesses, 4that is to say, alternate strips 17, or every third or fourth such strip 17 may appropriately vbe of double thickness to the thickness of the remainder of the strips 17. The last named detail of lstructural combination may be 'eX- fended to any other desired relative'differingrange of thicknesses for successively disposed .'strips 17 carried by Woven metal element16, but substantially as good results may also be had when the thickness, as well 'as the width of members 17 is uniformly The strips 17 are appropriately and permanently cemented to Woven metal mem` ber l16 by means of sodium silicate cement 18 or ordinary waterglass of commerce. The strips A17 may suitably be applied to member 16: in spacedrelation by drawing `each strip over a small supply ofthe aforesaid cement, and promptly and smoothly applying each said strip 17 and rubbing `same gently down on the material 16. The said cement sets rapidly and holds the strips 17 i tenaciously to the material 16.` At the same` time, the cement 18 normally penetrates through the woven metal material 16, and

causes the materiall6 to adhere to the fabric at a plurality of small areas correspond- ,ing to the position of the strips 17 on member 16. Cement 18 is sufficiently electrically conductive even after it has set into crystal-like fornito electrically interconnect the strips 17 and metal material 16.

A terminal 19 may be brought out so that electrical potential can be applied te the entire air permeable electrode. thus constructed. The air permeable electrode 3 thus is prepared as a laminated porous structure having a plurality of soft metal areas afforded by strips `17, and is essen- I tially iieXible and capable of acting in the function of a sound emitting member analogous to the similar property of the Vdielectric diaphragm 1 aforedescribed. The

vibrations of the air permeable member 3 Yare observable in normal servicel thereof.

Asregards the relative area andispacing of the strips 17, considerable latitude is afforded anyone skilled in this art Without greatly affecting the result. It is preferred, however, in view of numerous tests,

and inorder to obtain 'the best range of' may be as-muoh as 1% or 1 inch. y The more wide spacing 1s more appropriate in the case of vmaterial for woven metal member 16, comprised by wire screen having inter-` Woven therewith spaced wires in one direction as aforesaid at intervals of yi inch or more.

I am describing the observedlimits of dimensions 'found' suitable for such reproducers, because the results obtainable by departures from' such .ranges are definitely proven to be less pleasing and to restrict the range of frequency response to limits narrower than such as are deemed tobe suitable for que lity response range.

Obviously, 'somel of the strips 17 may be made Wider than others, but no advantage is obtainable by such modification which c'annot be :more conveniently obtained by coordinated spacing. and selection of the dimensions of the strips 17 of uniform size. In'the case of tinsel cloth for member 16, thestripsy 17 should be applied crosswise over member 16 so as to interconnect electrically the individual spaced tinsel metal strands of said tinsel cloth. The most suitable width for strips 17 is preferred in the range l@ inch to 5);/8 inch, not only for convenience of construction, but because a better air permeable electrode with better operating characteristics thereby results.-

By the term air permeable77 is meant that characteristic of the laminated struc ture described for flexible member 3 whereby air can freely flow through the muslin or fabric member 15, and the woven metal member 16 at portions not covered by strips 17. At the same time, when member 3 is operated or flexed the movement of the strips 17, as well as the solid portion ofA member 16 thereof, and the solid portion of member 15 thereof is able to distribute force to a considerable amount of air and cause sound waves to be emitted by member 43.

As will presently bc set forth, both memspect to the members 1 and 3. The energy transmitted to the air medium at each such transient instant largely propagates straight from the members'l and 8 for a considerable distance, and does not attenuate as rapidlyl as in the case of other -types vof sound emitters. Furthermore, the sound energy so setup when members 1 and 3 are stressed by vapplying varying electrical potential thereto strikes the surrounding air1 over a relatively large distributed area. It is an observed Afact that a listener at a distance ofsay tive feet from such a reproducer appears to hear the emitted sound'at substantially the same intensity as when positioned fortyl feet awaytherefrom. v

It may be here remarked that :a laminated lstructure as aforedescribed for member 3 is relatively dead lto sound, per se, and has substantially no forced vibration characteristic when. stressed.`

' The initial tension at which member 3 issupported on .frame 11 is not critical, but

greater -should in any case preferably be .than the tension, at which member 1 1s supported on frame 5, but not so large that member 3 cannot freely vibrate in operation.

Owing to various sizes and operating circumstances, the exacttension maybe widely` varied within limits easily determined by brief trial inany particular case anyone skilledfin the art, so that the moet pleasing result is readily arrived at by one or two observations. The minimum tension in bled without the use of means, such threads 4 interposed, the reproducer of Fi l would still be operative and suitable ina l respects if the amplitude of. vibration is kept below the point at which rustle or back-lash noises begin. However,for large amplitudes and in order to obtain a relatively high eiiiciency of response, I find that means such as elements 4 are essential to avoid" rustle noise. The means employed are, for eXample,-shown as fabric threads 4,

but any equivalent material of like general properties may be used'for the purpose.

It will be noticed that the threads 4 are preferably of non-conducting material, such as silk, linen or cotton in the common form, sold as thread or twisted thread or floss 1n the market. Strips or thin ribbons of in-` sulating material may also be used for elements 4. I have determined that various sizes of such threads are suitable for elements 4, provided that the spacing between successive threads 4 is proportioned according to the thickness. A few examples of thread sizes and spacing between threads 4' found suitable are listed herewith in order of merit. If wires or' insulated wires are substituted for the threads 4, an operative result may be had, but at much reduced efciency and with incomplete mitigation of rustle noises. Also if the threads 4 vare continuously fastened to either memberl" or member 3, the result .is notas good as when they are not :so fastened, but permitted merely to lie against the portions of members 1 and 3, free to move-or roll or twist in service.

The following table indicates an 'exempliicationof thread size and spacing betweenV threads suitable for the purpose:

i Approxi- Thread material Size mate Spacing diameter v Inch Spool'cotton 90 003 y2 to 1 inch. Spool cotton 70 004 M to 1% inches. Spool cotton. 60 .005 1 to 1% inches. Spool cotton. -i 8 01 21/2 to 3% inches. Spool si1k A 0035 to 1% inches. Spool linen 013 3 to 4% inches.

thread used, the closer same may be spaced for elementsv '4, and that the thicker the threads are, the further they must be spaced. Also as lthe thickness of the threads increases, such increase is accompanied by some loss of eiiciency. For the stated reasons, a'thin thread relatively closely spaced is preferred.

It may be remarked that the thinner the The thickness of the thread for elements 4 also depends on the thickness of the material of diaphragm 1 in the ratio that the thinner the material of diaphragnrl is, the i' thicker 'the material of threads 4v may be without loss of operating efficiency.'

The preferred structure, as shown in Fig. 1, may,l for example, have threads 4 of No. spoolcotton spaced 9/4 inch apart, `and tensioned sufficiently to lie against member 3. 'Lhen upon completion of assembly such threads 4 lie sandwiched between members 1 and 3 in the form of substantially spaced rows of twisted fabric free to move or alter .their positions under the action of stresses.

llO

Under normal use, the polarizing potential applied to electrode 2 and member 3 causes member 1 and member 3 to be attracted towards'each other with suiiic'ient force to draw portions of elements 1 and 3 adjacent to.

threads 4 closely against members 4.

In the case of a thin silk diaphragm material for membrane 1, this normal effect is s uiicient to make ridges visible -on the foil surface 2 corresponding to points of contact of membrane 1 against threads 4. An important new result is, however, attained in that the threads v4 are substantially non? conductive, so that the electrostatic force of attraction holding member 1 against threads 4 is relatively less at such points of contact. As a matter of fact, the residual force due to adhesion, friction, retentionof dielectric diaphragm 1.

strain in material 1 and/or vacuum suction effect is easily broken downas rapidly as necessary, due to the presence of the thin non-conductor threads 4. Such threads 4 are further able to roll or twist, as well as flex, with respect to members 1 and 3, so that adhering friction effects are substantially minimized, thereby permitting manimumresponse of members 1 land 3 to the applied electrical stresses.

A further fact is that upon returning from any particular 'transient force which separates member-i1' from member 3, the elasticity .Causes members 1 and 3 to tend to strike together. Such back-lash effect normally would produce undesired rustle noise, but due to means 4 the return shock is first absorbed by having the return force compress against threads 4 so that most of the area of members 1 and 3 does not contact until substantially all of the return force due to elasticity is so broken and dissipated. The operation is identical in either case, whether threads 4 are wound in spaced relation around member 3 carried on frame 11 or similarly supported by frame 5 adjacent to member 1.

In the other operating case, where member- 1 and member 3 have been transiently drawn as close as possible together by electrical stress due to the application of op erating potential to electrode surface I2 and air permeable electrodev diaphragm 3, elastic forces and/or' assisting forces due to applied electrical stresses normally compel the memrial 16, and since further the small diameter4 of the threads 4 leaves a thin line of contact with respect to members 1 and 3', airis freely admitted to break any vacuumsuction effect between strip members 17 and This desired effect is assisted by twisting action of the threads 4 influenced by the vibratory stresses applied to members 1 and 3. Any particular section or portion of membrane 1 is thereby permitted to flex and/or roll about threads 4 as a fulcrum with respect to member 3, and similarly each thread 4 acts as a fulcrum vfor. the free motion kof element 3. The actual result of this novel structure is that back-lash noises or fuzzy rustle sounds are eliminated at even the maximum amplitude of vibration of members 1 and 3.

The operating circuit Any suitable operating circuit may be,

employed to actuate the capacity reproducer set forth. Thus,` in Fig. .2` essentially, a

source of polarizing potential 20 normally causes electrode surface 2 to be attracted toward air permeable electrode 3, and press membrane 1 against threads 4. ThenA when fluctuating or. alternating currents or lvoice or sound varying potentials are applied to electrode 2 and electrode 3, members 1 and 3 arecaused tomove exactly in response thereto. The polarizing voltage supplied by source 2() may be afforded by small series connected batteries or a small transformer rectifier resistance capacity unit in customary manner. Its value should be well below the`breakdown limit ofmaterial used for diaphragm 1, and also higher than the largest peak voltage of the impressed voice or audio frequency currents. A practical value for the polarizing voltage, for eX- ample, is volts, direct current.

AThe reservoir condenser 21 should have a,

capacity of at least 1/2 'mfd. to keep the capacity reproducer charged when same is operated by a temporary electrical fluctuation of considerable magnitude, as when a percussion instrument is 3.11m; ueproduced In some cases, as for example, when the operatingpaudio current is obtained from a phonograph pick-up apparatus, a filter circuit 22 may appropriately be connected vbetween the-customary vacuum Vtube amplifier unit 23 and the capacity reproducer 24 to eliminate scratch sounds or other undesired noises. The use of terminal `resistance 25 in combination with capacity 26 permits reproducer 24 to be used with an amplifier unitv 23 which .need not of itself be constructed to match the impedance of reproducer 24. Such an arrangement permits reproducer 24 response free from disturbing noises. Due to the improved construction set forth, even the reproduction of loud sounds set up bv percussion instruments does not permit back-l lash effects to interfere with true response thereto free from buzzing soundspreviously found when threads or equivalent means 4 were not used.

In F ig. 3, the diagram illustrates the most probable theory of operation whereby rustle noises due to back-lash are avoided. sidering a small sectioned portion of the membrane 1 adjacent to one thread 4 and the co-operating portion of air permeable electrode 3, it will be evident that thread 4 may serve as a shock absorbing roller or fulcrum to break the return force normally tending to cause member 3 and member 1 to strike together. Also element 4, by its small area of contact and ability to rollv or twist, permits air to rapidly break vacuum suction causing adherence 'of element 17 to membranel when stresses draw these parts tol gether with rapid acceleration. In general, the two diaphragms l and 3 may operate in` opposed pbase,lthat is to say, with both unit portions of member l and 3 pushing the surrounding .air outwardly at a particular instant. I'lowever, if thread or like means el are not employed, there may be sufficient temporary adhesion ofv member l to member 3 to cause same to temporarily combine as a single laminated diaphragm, thereby introducing distortion and loss of efficiency. The means i prevent this undesired possibility, previously observed to be a fact in operation, when large values of operating electrical stresses were employed.

IVhile I have endeavored toset forth the most probable theory'of the operation, and to explain the function of the back-lash preventing means 4, my invention is not to be understood as depending` upon such theory because the structure exemplified yfor the purpose is demonstrated to be fully operative to attainithe objects sought, regardless of the exact nature of operating characteristic causing'the desired action. The result too is attained without loss of efficiency or volume of response. So too, where I have specified exemplifications of suitable dimensions and proportions, same are to be considered as desirable and not necessarily limiting proportions because in many cases nearly as good results can nevertheless be obtained by wide departures from the exact values indicated 'as demonstrated to be suitable. l

In general, however, close attention to details of structure specified will afford most pleasing and efficient results. I believe that I have now fully set forth my invention and the step forward in this art which it teaches, so that various changes may be made within the spirit of the invention and the scope of the appended claims. .f

I claim:

l. Av capacity reproduce'r consisting of operating members comprising tWo electrodes with a dielectric between and a vplurality of separately spaced flexible means interposed between said electrodes to mitigate vthe back-lash effect thereof.

2. A capacity reproducer consisting of operating sounding electrode members and unwoven threads interposed therebetween.

3. A capacity reproducer consistingy of' sounding electrode members an`d spaced unwoven threads sandwiched therebetween.

4,. In an acoustic condenser employing sounding members, means to preventrustle -noises at large amplitudes of response of said members consisting of loosely disposed spaced insulatihg elements `interposed between said members.

5. A capacity reproducer consisting of an air permeable electrode, a co-operating dielectric diaphragm therefor, an electrode coating carried byI said dielectric dia-y pbragm, and flexible spaced insulator elements loosely stretchedbetween said dielectric diaphragm and said air permeable electrode.

(5. A.A reproducer consisting of a plurality of co-operating sounding members, means to actuate said members, and spaced thread shaped elements interposed between said members.

v7. A capacity reproducer consisting of an air per'meable'electrode, a co-operating dielectric diaphragm therefor, an electrode carried by said diaphragm, and spaced sounding members, means to actuate said sounding members, and a plurality of spaced linearly disposed insulator elements sandwiched between said sounding members.

l0. In an acoustic condenser, structure for an air permeable electrode therefor consisting of an electrically conductive flexible woven material, a plurality of spacedmetal strips fastened thereto, and a plurality of spaced thread-like elements movably supported with respect to said metal strips.

11. In an acoustic condenser, structure for a dielectric diaphragm and its conductive coating consisting of a dielectric impregnated fabric, a coating of finely divided powder on one surface of said impregnated fabric, a perforated thin metal foilcoating on the other surface of said impregnated fabric, and an insulating adhesive disposed to hold said perforated foil on said fabric.

12. An acoustic condenser consisting of two flexible stretched sounding-members, means to actuate said members, spaced flexible 'elements disposed between said members, and means to maintain one/of said sounding members under less tension than the other.

13. A capacity reproducer consisting of a dielectric diaphragm, a conductive-coating on said diaphragm, a (1o-operating air permeable'electrode held adjacent to said diaphragm, and thin spaced flexible elements disposed between said diaphragm and said air permeable electrode.

In testimony whereof, I have hereunto set my hand' this 30th day of July, 1929.

' ,PHILIP E. EDELMAN.

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