US2297218A - Loud-speaker - Google Patents

Description

SCP 29, 1942- l H. E. HENRxcH ETAL 2,297,218

LOUDSPEAKER Y Filed April 22, 19,58

Zda:

i claims.

Patented Sept. 29, 1942 um; E. nennen ma omliviernng, nerim, t Germany; vested ln-,the Alien'lroperty Custo- V Application April z2,

In Germany 1938, serial Nu. 203,632

April-24, 1937 1s claim.L (ci. lai-sz) This invention relates to loudspeakers, and more particularly to the diaphragms an immediately associated components thereof. While the v invention is not hunted thereto, it has been particularly illustrated and described in connection with a loudspeaker of the electro-dynamic type.

A problem' in the design of loudspeakers is the attainment of a satisfactory response over a large .frequency range, from very low to very high frequencies, with a single loudspeaker. The electro-acoustic translating unit proper-e. g., the voice coil of the electro-dynamic speaker-can readily be made to respond over a wide frequency range, but it is diiilcult to make the diaphragm radiate properly over such a range. The diaphragm ordinarily has many modes of vibration;

is nnfavorably variable in its effective stiffness at the several frequencies; has (for example at the usual junction oi the cone diaphragm and its peripheral attaching means) abrupt and appreciable discontinuities in its stillness between they exciting region and the peripheral support, givl I I a thickness tapered in an especially favorable manner from the exciting region to the peripheral Y support.

It is an object to provide a. tapered diaphragm oi' a material permitting a large thickness at' the exciting region without entailing excessive mass of the diaphragm.

Itis an object to` provide a proper peripheral supporting of the diaphragm while minimizing tendencies toward reflections and standing waves. It is an object to provide a generally improved Idiaphragm for a wide-rangeloudspeaker.

It is an object `to provide improved com-binatlons of the diaphragm and its peripheral attaching means.

Itis a general object tol provide an improved wide-range loudspeaker. 1

Other and allied objects will more fully appear from the following description and the appended In the description reference is had to the accompanying drawing, of which:

Figure 1 is a vertical, central cross-sectional view of a loudspeaker oi' the electro-dynamic type wherein the invention has been embodied in a simple form;

Figure 2 is a partial similar view of a loudspeaker in which the inventionhas been embodied in a somewhat modiiied form: I

Figure 3 is a fragmentary front elevational view of the diaphragm and peripheral attaching means of the loudspeaker of Figure 2;

Figure i is a fragmentary, enlarged 'view generally similar to a portion of-Figure l, but illustrating the embodiment of the invention in a vfurther modiiled form; v

Figure 5 is a fragmentary, enlarged view of the nature of Figure 4', but illustrating the embodi- -ment of the invention in a still further modied form; and i Figure 6 is a fragmentary iront elevational view of the loudspeaker of Figure 5. e

Referencey being had to Figure 1, there will be seen a conventional dynamic loudspeaker magnetic structure comprising the cup-shaped :member or pot I, the cylindrical core 2 extending forwardly from the closed end or rear of the pot I and co-axial therewith, and the iront plate 3 closing the pot and centrally apertured to pass the core 2 with an annular gap 4, co-axial with I and 2, between it andthe core. A field coil 5 is schematically shown surrounding Lthe core 2 within the pot, it beingunderstood that the excitation of the ileld coil by direct current will produce a eld of high intensity across the gap 4.

Within the gap 4 is locatedan annular voice coil B; and it will be understood that 'when sound-representing electric oscillations are supplied thereto the voice coil 6, and the components with which it is secured and which are next described, will execute a sound-representing vibration in an axial direction.

The voice coil 6 may be wound and secured around the extremity of a light, thin-walled and nonqmetallic cylinder 1'; this cylinder is support- Y ed, coaxially with the gap 4, for vibratory axial. movement. A front support for the cylinder is provided through the intermediary oi' the diaphragm, as will hereinafter appear. A rear support for the cylinder may be provided just a little forward of the voice coil 6; it may comprise three or more light, flexible ngers 8 having first extremities secured to the cylinder 1 and extending preferably radially-therefrom, and having second extremities secured to front plate 3' as through spacing pillars 8. The lingers I, taken together,

55 may be considered a "spider for the support of embodiment of the invention is of very appreciable thickness in the exciting or central region, the cylinder 1 may` extend from the rear into the diaphragm for a considerable distance, insuring a particularly firm union of the diaphragm and cylinder. It will be apparent in the structure so described that the voice coil 6, and cylinder i rigidly coupling it to the diaphragm It, are the immediate exciting means for .the diaphragm;

but it will be understood that in its broader aspects the invention is not limited to this particular form of exciting means, nor to the electrodynamic operation thereof, these having been chosen for illustrative and explanatory purposes.

According tothe preferred embodiment of the invention the diaphragm Iii has a thickness which tapers from the exciting region to the diaphragm periphery.` Preferably the diaphragm is in the form of a solid conoid--L e., a solid body having the approximate though not necessarily the exact shape of a cone-coaxial with the cylinder l, rearwardly convergent to be excited in its apical region, and having its base Ia facing forwardly. In Figure 1 the diaphragm has been illustrated as a solid conoid whose altitude (or thickness measured parallel tothe axis) tapersor decreases, with increasing distance from the axis, in a smooth concave curve. While the curvature of the thickness may be according to any of a variety of mathematical laws, an exponential curvature has proven peculiarly effective in providing proper relative stiffness characteristics, and uniformity of response, at the various frequencies throughout a particularly wide range. While the exponentialcurvature may be reckoned from either the axis or the surface of the cylinder i or from therebetween, a reckoning approximately from the cylinder surface has been assumed in Figure l.

It is desirable that the thickness of .the diaphragm in the exciting region (or maximum altitude of the conoid) be relatively largefor exampie, a major fraction of the radius or even of the diameter of the front of the diaphragm (or base of the conoid). This not merely' facilitates the firm "nien of the diaphragm with the cylinder l or its equivalent as abovementioned, but in general provides `a rm central diaphragm portion, permits the greatest ease andvaccuracy in `Af the tapering of the'thickness, and takes fullest advantage of the tapered formation-' Such a cenmaterial of the light, aeriferous character is the pith of certain plants, typically the pith of the elder. Artificial material of similar physical nature is preferably employed, however-such, by way of non-limitative example, as might be successfully used for heat insulation purposes. `Particularly in the artificial materials, the air cells may be substantially uniform and uniformly dispersed, and the materials may be considered homogeneous.

The base substance of the diaphragm material may be for example a uriatic-formaldehyde condensation product, an artificial resin, a phenolic plastic, a cellulose or latex derivative, a caesingelatin product, or the like; such a substance may be processed mechanically or chemically to produce minute air cells therethrough-a typical chemical processing for the purpose comprising the production and dispersion of a gas through the substance in process, as bythe interaction of certain materials being mixed into the substance.

These aeriferous materials may have a weight per cubic foot of the order of less than 10 pounds, and typical ones a Weight per cubic foot of less than 3 pounds-e. g., of 21/2'pounds or even less. A particular articial material whose characteristics have been found good for the instant purpose may be mentioned, wholly non-limitatively, as the caesin-gelatin product commercialized for other purposes under the trade name of Cellglue; this has a weight per cubic foot of the order of 21/2 pounds.

It may be pointed out that, over and above their lightness, these homogeneous, aeriferous materials, with their cellular structure, are inherently characterized by appreciable internal damping; this by itself, and independently of other features of the invention, appears beneficially to reduce the effective transmission of waves through, and the reflection thereof at the periphery of the diaphragm.

In general, the diaphragm may be cut, machined or 'otherwise formed from the material already prepared; or the material may-in its original preparation, for example-be directly molded into the desired diaphragm form. While many of the preferred materials may be moisture- (as well as fire) resistant, it may frequently be desirable to lacquer or otherwise seal the surface of the prepared diaphragm. y

Attention now being directed to the support` ing of the diaphragm at its periphery, it will be seen that in Figure l the periphery` im) of the diaphragm is directly secured to the stationary support-i. e., to a supporting ring it secure with 'respect to the pot l, to which ring the diaphragm periphery may be clamped as by .a clamping ring i?. The rate of curvature at which the thickness of the diaphragm is reduced is made great enough to result in a very thinperiphery Elib; the resulting flexibility at and near the periphery may be relied on to permit the proper piston-like movement of the central portion. To approximate the effect of an extremely thin periphery, while actuvally employing the minimum thickness. necessary for sufficient mechanical ruggedness, it is helpful locally to soften the diaphragm at and adjacent the periphery, for example by treatment of-this region, during or after the formation of the diaphragm, with suitable plasticizing agents.

In Figures 2 and 3 there is illustrated aI modified form of the invention. Herein the diaphragm, designated as 20, is similarly excited to the diaphragm iii of Figure 1, and may be of the same material. It again has the exponentially tapering thickness, but its bas'e or front surface l20a by way of example has been shown as dished or slightly concave, which formation is frequently helpful acoustically for the minimization of tendencies toward rectification at very high frey i 9,297,218 quencis. Like that of the diaphragml In, the' peripheryl 2lb of the diaphragm Il is reduced t0 a very small thickness, but it is not in itself used as an attaching means. Instead there is secured on or formed in .the front surface 20a of the diaphragm a iiexible web or mesh 2 I, this being continued outwardly beyond the diaphragm periphery; this web may for example be a pre-formed web, as of strong thread fibres. `This web is used as the attaching means, being glued to the supporting ring 2,6; this ring may be similar to ring ls of Figure 1, excepting that 1t is df slightly larger diameter than the diaphragm periphery,

in stiffness. Any residual` discontinuity, however,

with this or' any of the other webs above described, may be still further reduced by treating the extending web appropriately, as with suitthe web 2i' crossing the annular gap 25 therebetween and being active in that 'gap to provide the requisite flexibility. Figure 3 illustrates in elevation a fragment of the combined diaphragm 20 and web 2|. i

The structure of Figure 1 completely obviates discontinuities in stiffness of the movable system from the exciting region to the peripheral support; and while the structure of Figures 2-3 inplurality of webs 3i', 3i" are secured between the laminations; while the webs may extend any desired distance toward the center of the diaphragm, they have been illustrated as extending only a short distance inwardly from the very periphery h. The several webs extend outwardly as does the web 2| of Figure 2, and are together secured tothe ring v26, which may be arranged as in Figure 2, as by gluing.

While pre-formed webs, attached to alreadyformed diaphragms or diaphragm laminations, have been shown in Figures 2-3 and 4, the invention also contemplates the use of a web formed in the diaphragm during the `formation of ythe latter; in this case it is not necessary that the web be pre-formed. This has been illustrated in Figures 5 and 6, in connection with the dlaphragm 40, which in configuration and disposition may for example be similar t`o diaphragm 20 of Figure. 2. In the diaphragm 40 there arey riphery 0b. Manyof these strands are caused to extend beyond the periphery 4Gb, and these extending strands are used as the peripheral attaching means for the diaphragm. Preferably the arrangementof the strands inside and out- `side the diaphragm is largely non-radialv and ner, for example by a clamping ring I1 as inA Figure l; In view of the integral formation of diaphragmA l0 and web Il, the diaphragm peripheral thickness may be run down to approximately the mere thickness of 'the web Il, prac-A tically eliminating altogether any discontinuity able varnishes, lacquers or the like, to alter its stiffness.

With loudspeakers constructed in accordance with the invention and properly baiiied in well understood manner, extremely favorable results have been obtained over such wide frequency ranges as 30 to 10,000 cycles. Reflections ancl standing waves are greatly minimized or substantially eliminated; vibration of the bulk of the diaphragm as a unit is very closely approximated; and practically the entire diaphragm mass is effective to establish a very low fre- .quency of resonancefof the vibratory system.-

While the invention has been described in terms of specific embodiments thereof, it will be vunderstood that no unnecessary limitations are pose- The following is claimed:

1. In a loudspeaker having an annular air gap adapted for magnetic energization, and a voice coil disposed within said gap: the combination of a hollow cylinder extending'axially into said gap and carrying said voice coil and supported for axial vibratory movement, and a solid diaphragm secured on said cylinder, said cylinder f penetrating into said diaphragm for a substantial distance. l

2. In a loudspeaker: a diaphragm having a portion adapted for connection with vibratory exciting means and having in the vibratory direction a thickness which is reduced exponentially with increasing distance, normal to said direction, from said portion.

3. In a loudspeaker: a diaphragm having a rear portion adapted .for connection with vibratory exciting means, having a concave forward face,

.and having in the vibratory direction a thickness which is reduced exponentially with increasing distance, normal to said direction, from said portion.

4. In a loudspeaker: a vibratile .diaphragm system at least substantially wholly composed of a solid conoidal diaphragm having a thin periphery -and having an apical portion adapted for connection with vibratory exciting means, of thick- .ness which is at least a major portion-of the diaphragm radius. f

5. In a loudspeaker: a solid diaphragmshaving a portion of substantial thickness adapted for connection with vibratory exciting means, said diaphragm tapering approximately exponentially in thickness from said portion to a thin peripheryA and being formed of a light, highly aeriferous material.

6. In a loudspeaker: a solid diaphragm having a portion of substantial thickness adapted for connection with-vibratory exciting means, said diaphragm tapering approximately exponentially in thickness from said portion to a thin periphery adapted for connection with vibratory exciting means and formed of a homogeneous, light and highly aeriferous material.

V9. In a loudspeaker: a solid diaphragm oi approximately exponentially tapering thicknesstv adapted for connection with vibratory exciting means and formed of a homogeneous, highly f aeriferous material characterized by appreciable internal damping.

10. In a loudspeaker including a peripheral diaphragm support: a solid diaphragm having a portion of substantial thickness adapted for conl nection with vibratory exciting means, said diaphragm tapering in thickness from said portion to a thin periphery and being formed of a light, highly aeriferous material, and said material being locally softened in the region adjacent said periphery and being peripherally secured to said support.

11. In a loudspeaker including a peripheralv diaphragm support: the combination of a solid, laminated diaphragm having aportion of substantial thickness adapted for connection with vibratory exciting means, said diaphragm tapering in thickness from said portion to a thin periphery and being formed of a light, highly laeriferous material: and brous web means secured between the laminations of said diaphragm and flexibly attaching said diaphragm periphery to said support.

12. In a loudspeaker including a peripheral l diaphragm support: the combination of a solid diaphragm having a portion of substantial thickness adapted for connection with vibratory exciting means, said diaphragm tapering in thickness from said portion to a thin vperiphery and being formed of a light, highly aeriferous material; and fibrous web means intimately imbedded in said diaphragm material adiacent said diaphragm periphery, extending outwardly from said periphery, and ilexibly" attaching said diaphragm periphery to said support. I

13. In a loudspeaker including a peripheral diaphragm support: vthe combination of a solid diaphragm havinga portion of substantial thickness adapted for connection with vibratory exciting means, said diaphragm tapering in thickness from said portion to a thin periphery and being formed-of a light,v highly aeriferous material; anda plurality of fibrous strands intimately vimbedded in said diaphragm material adjacent said diaphragm periphery, extending outwardly therefrom, and flexibly attaching said diaphragm periphery to saidf'support.

14. In a loudspeaker including aperipheral diaphragm support: the combination of a solid, tapered diaphragm centrally adapted for connection with vibratory exciting means; Vand brour` web means intimately imbedded in :the material of said diaphragm adjacent the diaphragm periphery only, extending outwardly from said periphery, and exibly attaching said periphery 'to said support.

15. Inv a loudspeaker including a peripheral diaphragm support: the combination of a solid,

.tapered diaphragm centrally adapted for connec- -wardly from said periphery, and flexibly attaching said periphery to said support.

, osKAR VIERLING. .HANS E.HENRICH.

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