US1799162A - Diaphragm especially for the reproduction of sound - Google Patents

Description

April 1931- R. GOLDSCHMIDT 1,799,162

DIAP HRAGM ESPECIALLY FOR THE REPRODUCTION OF SOUND Filed May 22 1928 3 Sheets-Sheet 1 April 7, 1931. R. GOLDSCHMIDT 1,799,162

DIAPHRAGM ESPECIALLY FOR THE REPRODUCTION OF SOUND Filed May 22 192 3 Sheets-Sheet 2 April 1931- R. GOLDSCHMIDT 1 1,799,162

DIAPHRAGM ESPECIALLY FOR THE REPRODUCTION OF SOUND Filed May 22 1923 3 Sheets-Sheet 3 NVSS Patented Apr. 7, 1931 UNITED STATES PATENT OFFICE RUDOLF GOLDSCH MIDT, OF BERLIN, GERMANY DIAPHRAGM ESPECIALLY FOR THE REPRODUCTION OF SOUND Application flled May 22, 1928, Serial No. 279,740, and in Germany September 1, 1927.

This invention relates to an im roved diaphragm especiall for the repro notion of sound. The fo lowing description is based chiefly on the example of an electrob magnetic telephone equipped with the improved diaphragm, but the latter may be equally advantageously applied to any other sound reproducing machine, for instance to an electro-static telephone, a loudspeaker and W a phonograph as well asa regulating, meas uring, and any other device, where power is transmitted through the medium of a diaphragm.

One object of this invention is to increase the elasticity of a given diaphragm.

Another equally important ob 'ect is to give a bend and a considerable radius of curvature to the otherwise only slightly curved practically straight, characteristic curve of elasticity which determines the deflection of the diaphragm under different loads or pulls.

These results are attained by means of certain stresses created artificially in the material of the diaphragm, so asto bring it more or less close to a state of balance (pseudo-astatic e'uilibrium). v

In order that t e invention may be more clearly understood reference is hereinafter made to the accompanying drawings wherein Figure 1 is a plan view of my improved diaphragm; Fig. 2 shows aisectional view of the improved diaphragm shown in Fig. 1

Figs. 3, 4 and 5, are diagrams graphically illustrating the effect of improvements in accordance with my invention;

Figs. 6 and 7 illustrate steps employed in the method of producing the useful stresses in thedia hragm of my invention;

Fi 8 s ows'the form which the im roved diap ragm of Fig. 10 assumes under t e pull of an actuating magnet system;

Fig. 9 illustrates the section of a diaphragm under the pull of the magnet system, 45 the dimensions bein the same as that of Fig.

8, but without the improvements according to my invention;

Figs. 10,11,12 and 13 are modifications of the method for producing an improved diaphragm; and

taking 8 in Fig. 7, is annihilated entirely, or to a large extent, by bending it into the form 1, Fig. 2, the depth of the bowl being reduced from f to This counter-operation, which, for the sa e of reference, may be called the stretching is to be more or less of a nature such that the diaphragm, after havin been stretched into an almost entirely fiat orm 1 or beyond this and held back in the new posia tion, retains some tendency to return towards its fornier shape 8 through latent elastic stresses.

The stresses are spread over the whole dia- V phragm, practically every square millimeter part in the vaulting and stretching. The efi'ect of this preparationis that the diaphragm is made to resist a strong magnetic pull and to adapt its characteristic tot at of the magnet, the meaning of which will be explained with reference to Figs. 3, 4 and 5.

In-diagram Fig. 3, P is the pull upon a diaphragm vertical to its plane, and D is the corresponding deflection. Character I refers to an ordinary diaphragm. If the latter is prepared as described above the characteristic changesto curve II in Fig. 3 or assumes the unsymmetrical sha c Fig. 4.v The characteristic can be shape atiwill and depends entirely upon the vaulting and stretching process.

' For the adaption of the characteristic of the diaphragm to a given purpose, the electro-ma netic tele hone is a good example. I

The pu 1 exercise by the permanent magnet u on the diaphragm de ends on their relative distance, a relation in icated by the characteristic of the magnet, curve III in Fig. 5. If the distance is zero the pull is 0A. If there was no magnetic pull it all, tho position zero or at least extremal;

of the diaphra would be at C. The dis-' tance 00 must such that, if the diaphragm is deflected until it touches the magnet, its elastic force OB exceeds the attractive force OA of the magnet by an amount of safety AB, so that the diaphragm cannot stick to the magnet. An ordinary diaphragm with a strai ht characterimic (IV in Fig. 5) would efle'ct into position F (distanoe OF), a ,1 point where the magnetic and elastic forces are equal. The position which an improved characteristic (curve V) would assume in'the magnetic field, would correspond to the point of intersection G (distance OG) of the curves III and Y. The angle of intersection ought to be very near acute. The charmay be so losely acteristic of elasticity Tadapted or assimilated to the characteristic III of the m etic force that through the differential action of both forces in the areanear -G the resultant elasticity of the diaphragm becomes almost infinite. The diaetic phragm practically floats in the ma field, this result being achieved under t e espronounce'd curvature of its characteristicthere is no danger of the diaphragm sticking to the ma et. Extreme'elasticity is combined with stability. Naturally the diaphragm connot be quite astatic over a wide range, but is very close to a state which in steam engineering and physics is called pseudo-astatic, a term which mi ht be used to designate such a condition 0 sensitiveness.

The pseudo-astatic state may be verified by holding the telephone to the ear and exercisin a small pressure upon the case of the telep one, thereby-compressing slightly the air enclosed between the tympanum and the diaphragm and noting the clickin noise due to the extreme sensitiveness of the diaphragm upon the slightest change of pressure.

The method of vaultin and stretching may be varied considerab y. I prefer the mode as illustrated by Figs. 6 and 7. The diaphragm 1 is pressed (vaulted) into the form. Fig. 6 and afterwards by pres re from below asindicated by the arrows, tra sfor-med (stretched) into that of Fig. 'l. The bevelhng (9) of the diaphragm along its circumference (like a mirror) is important. It

gives way and adapts itself automatically and permanently to the shape of the diaphragm, when the latter undergoes its transformation. This helps to secure the bending momentums and is essential in producing din.- phragms with practically equal properties.

t forms a buffer between the frame or rim and the diaphragm proper, thus protecting the latter against natural as well as accidental changes.

The unsymmetrical shape Fig. 4, which is very useful in electromagnetic telephones, is

obtained by stretching the diaphragm so that it bulges but somewhat beyond the flat form a1 measurements. Fig. 8 refers to a diaphragm in accordance with this invention, assuming the shape. X under the influence of the magnet. This shape changes to Y, if a small direct current is passedthrough the telephone coils upon the magnet. For an ordinary diaphragm with the identical general dimensions but without the artificial stresses the corresponding forms are those of F ig. 9. Figs. 8 and 9 are directly comparable, the

cross-hatched areas illustrating the larger volume of air displaced under influence of the same current by the diaphragm Fig. 8 in accordance with this invention.

Figs. 10-13 illustrate a mode of stretching carried'out at the same time as the diaphragm 1) is'insered into its frame (2), the

vaulting having been done beforehand.

The permanent maintenance of the stresses in the diaphragm is of fundamental importance. Before providing proper means ,to se- 1 curethem, I have had the experience that a number of. originally excellent diaphragms had become perfectly useless within 24 hours, others within a week. One ofthe protecting means is the bevelling (Fig. 7). Others are indicated in Figs. 1,2,6 and 8, where the diaphragm is secured in a strong frame by corrugating the rim during, the process of fixing it in the frame.

In order to guard against extension and contraction through the influence of temperature changes, the material of the frame ought to be chosen so that ithas practically the same coeflicient of extension as that of the diaphragm itself. An iron diaphragm ought to have an iron .frame, if possible. If, however, the latter .is firmly screwed against a different material, a bi-metallic action may again make the diaphragm alive to the temperature of its' surroundings, destroying its qualities through warping. This influence has been borne out my early experiments with a telephone equipped with the new diaphragm, the latter becoming useful only after warming it up by holding the tele-.

phoneto the ear for several minutes.

To make the diaphragm independent of its neighbourhood flexible insertions (10) Figs. 14-15, for instance paper or rubber rings are provided which insulate the diaphragm mechanically.

If such insertions are'made very flexible and the shape of the diaphragm and its rim such that it becomes in itself resistant against alteration of the interior stresses, the frame (2) may be reduced to plain rings which are pressed against the rim (11) provided that the metal is not too thin.

With a very thin diaphragm of large diameter, however, it is necessary, not only to insert it securely, into a strong frame, but to doso before the vaulting or anyway before the stretching operation is carried out, as otherwise there is a chance that the diaphragm has become an absolutely different one, after having been placed into the apparatus of which it forms a part.

Claims:

1. The method of creating artificial stresses in a diaphragm which consists in forming the diaphragm into a vaulted shape and subsequently applying permanently bending forces to the diaphragm in the direction from the convex to the concave side of the original vaulting for shifting said diaphragm in a direction opposite to the vaulted positlon thereof.

2. The method of creating artificial stresses in a diaphragm upon which a perm'anent pull is exercised which comprises forcin the material of the diaphragm into a vaulte shape and thereafter deforming said diaphragm to a position wherein the combined action of the external and internal forces are such that the diaphragm operates near a point of fiexure of its characteristic curve.

3. A sound reproducing diaphragm comprising a sheet of material which is subjected to artificial stresses, a clamping device, the rim of said diaphragm being rigidly secured in said clampingdevice, said diaphragm having an annular beveled portion pressed therein intermediate the clamped portion and-the central portion thereof, said central P01131011 having the material thereof compressed for establishing permanent internal forces in said diaphragm.

4. A diaphragm comprising a sheet of magnetic material, a clamping device for securlng a rim portion of said diaphragm at its periphery, said diaphragm having a central portion and an annular bevelled ortion pressed therein intermediate the o amped 'portion and said central (portion, said cen tral portion being stampe with dies having the shapes of continuous curves first in one direction and then in the opposite direction, and said central portion having the material thereof compressed for establishing permanent internal forces in said diaphragm.

5. A sound re roducing diaphragm comprising a sheet 0 material having an annular rimportionand a central portion, said annular rim portion being fixed in a retaining restoring saidv diaphragm to a position ;ap-

proximating the original position of the diaphragm with internal forces established therein and maintained by said retaining frame.

6. The method of forming a sound reproducing diaphragm which consists in applying forces to the diaphragm to press the dlaphra'gm into an arched shape and subsequently applying forces to the diaphragm in the opposite direction to flatten the arched sha e diaphragm into a substantially plane sur ace for establishing permanent internal forces within the material of the diaphragm.

7. A sound reproducing diaphragm comprising a sheet of material having an annular rim portion and a central sound reproducing surface, means for gripping said sheet of material at its rim portion, said diaphragm being vaulted in the central portion thereof in one direction and flattened substantially throughout the vaulted portion by forces applied in the opposite direction for establishing permanent internal forces within the material of the diaphragm.

8. A sound re roducing diaphragm comprising a sheet 0 material having a rim portion, means for gripping said rim portion, the central portion of said diaphragm being 'vaulted in shape in one direction and thereafter deformed from the vaulted shape in the opposite direction to a position in which the internal structure of said diaphragm is maintained under a state of permanent internal stress.

9. In a sound reproducing diaphragm, a sheet of material having a rim portion and a central portion, a frame for gripping said mm portion, said frame having substantially the same coefficient of expansion under conditions of rising temperature as the materlal of the diaphragm, the central portion of said diaphragm being vaulted first in one dlrection and subsequently deformed in the opposite direction for maintaining said diaphragm in a condition of permanent internal stress.

A sound reproducing diaphragm comprising a sheet of material having a rim portion and a central portion, a frame structure surrounding said rim portion, thermal insulation means disposed between said frame structure and said rim portion, said central portion being vaulted first in one direction and subsequently deformed in the opposite direction to maintain the internal structure of said diaphragm in a condition of internal stress.

11. The method of forming an accoustic diaphragm to be actuated by the force of an external field which varies at different points in a gap, which consists in vaulting said diaphragm in one direction by stamping with a curvilinear die, and counter-vaulting by stamping in the opposite direction in such manner that the restoringforce of said diaphragm is approximately equal to said external field force over a substantial part of the working portionof said gap. r

12. The method of forming an acoustic stamping with a curvilinear die, and countervaulting by stamping in the opposite direction, in such manner that the restoring force of said diaphragm is approximately equal to said external field force over a substantial part of the working portion of said gap.

14. The method of forming an acoustic diaphragm to be actuated by the forceof an external field which varies atdifierent points in a gap which consists in clamping said diahra m in a mountin rin stam in said U 7 portion bent from the diaphragm withdie and counter-die to form,

a central arched portiogf,l and an annular rim rection opposite tothedirection of such vaulting, and then applying pressure from the convex side of said vaulted portion to cause said vaulted portion to assume a substantially flattened form, whereby the restoring force of said diaphragm is approximately equal to the said external field force over a substantial frequency of an acoustic diaphragm which 3 points in a gap, a mounting frame of a matepart of the working portion of said gap.

, 15. The method of lowering the resonance consists in vaulting said diaphragm by stamp ing with a' curvilinear die, and.counter-vaultposite direction.

"ing said diaphragm by stamping in the opat position in a diof an external field which varies at difierent points'in a gap, a mounting frame in which said diaphragm is clamped, heat insulating pieces insulating said diaphragm from said frame, said diaphragm being vaulted and counter-vaulted by stamping operations in opposite directions whereby said diaphragm possesses a restoring force approximately equal to said external field force over a substantial part of the working portion of said phragm to be actuated by the force of an external field which varies at diflerent points in a gap, which consists in clamping said diaphragm tightly in a mounting frame, andapplying permanent compressive forces in said diaphragm by vaulting said diaphragm in one direction by stamping with a curvilinear die, and counter-vaulting by stamping in the opposite direction.

18. The method of forming an acoustic dia- 19. The method of forming an acoustic diaphragm to be actuated by the force of an external field which varies at different points in a gap which consists in clamping said dia phragm in a mounting ring, stamping said diaphragm with die and counter-die to form a centralarched portion and a frusto-conical annular zone, and then applying pressure .from the convex side of said vaulted portion to cause said-vaulted portion to assume a subta'ntially flattened form, whereby the restoring force of said diaphragm is approximately equal to the said external field force over a substantial part of the working portion of said gap.

In testimony whereof I afix my signature. RUDOLF GOLDSGHMIDT.

I 16. In an acoustic device,an acoustic diaphragm adapted to be actuated by the force of an external field which varies at diflerent rial having the same temperature-coefficient as said diaphragm in which said diaphragm 1 is clamped, said diaphragm being vaulted and counter-yaulted by stamping operations in opposite directions whereby said diaphragm possesses a restoring force approximately 1 equal to said externalfield'force over a substantial part of the working portion of said 17..In a acousticj'device, an acoustic dia- I phragm adapted to be actuated by theforce

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