US1484471A - Sound recording and reproducing instrument - Google Patents

Description

Feb. 19, 1924.-

W. E. CLIFTON ET AL SOUND RECORDING AND REPRODUCING INSTRUMENT Filed June 21. 1921 a a a Patented F eb, 19, 1924.

UNITED STATES PATENT OFFICE.

WILLIAM ERNEST CLIFTON AND J'QHN STURTON EWART, OF NOTTINGHAM, ENGLAND,

ASSIGNORS TO THE CLIFTOPHONE LIMITED, OF LONDON, ENGLAND.

SOUND RECORDING AND REPRODUCING INSTRUMENT.

Application filed June 21, 1921.

T all Q0/1077), may concern:

Be it known that we, WILLIAM ERNEST CLIFTON and JOHN STURTON EWART, subjects of the King of England, both residing in Nottingham, England, have invented certain new and useful Improvements in Sound Recording and Reproducing Instruments, of which the following is a specification.

This invention consists in improvements in or relating to sound-recording and reproducing instruments for use with gramophones and like machines of the flat discrecord type in which the stylus bar is pivoted intermediate of its two ends in the sound box casing and is directly connected at its inner end to the diaphragm or a part rigidly connected therewith without the interposition of a link, and refers particularly to the construction of a diaphragm or vibratory membrane therefor. The principal object of the invention is to provide a diaphragm by which a purer tone and a better balance between treble and bass regis tiers will be obtained than has been possible 5 heretofore, and to enable the diaphragm, where it is connected to the stylus bar, to move readily through substantially the same are as that through which the end of the stylus bar moves.

In instruments of this type hitherto, hereinafter referred to for brevity by the term sound-box the diaphragm has generally been constituted by a comparatively stiff and elastic disc of material rigidly held around its margin in the casing of the sound-box. To the centre of the diaphragm is firmly connected one end of a stylus-bar or lever pivotally mounted intermediate of its length in the sound-box casing so that it can oscillate in a plane at right-angles to that of the diaphragm. The-other end of the lever fitted with a. needle the point of which serves either to record on a plastic body vibrations imparted to the diaphragm or, in reproducing, to be oscillated by the record to transmit vibrations to the diaphragm. In such a construction the sty lus-bar, which oscillates about a fixed axis, endeavors to mov e that point of the diaphragm to which it is attached in an arc struck from the axis of pivoting but a dia phragm of the nature referred to is not adapted to follow this movement. Moreover, the diaphragm is not adapted to Serial No. 479,379.

be moved to any appreciable extent without stretching or distorting the material of the diaphragm unless the edge of the latter is free to move in its connection with the sound-box.

Diaphragms have been suggested wherein the central portion has been composed of relatively 'stifi material and the portion surrounding it has been of more flexible material. In such a case the stiffened central portion was secured at its centre to the end of the stylus-bar and this again was not found to produce the satisfactory results ob tained with the improved diaphragm of this invention.

According to the present invention a diaphragm is composed of flexible and substantially non-resilient or only sli htly resilient material and has a relatively still portion which is disposed in the middle or partly in the middle of the diaphragm and is formed for connection with the inner end of the stylus-bar at a position which is eccentric in the said relatively stifi' portion. Thus the latter may conveniently be constituted by a radial strip having straight, parallel or tapered sides 01' of lozenge or oval shape, the strip being formed for connection with the inner end of the stylus-bar at or near an edge which is adjacent to the centre of the diaphragm.

The term .non-resilient, as applied to the main portion of the diaphragm, is to be understood to mean that the portion thus denoted is non-resilient as compared with diaphragms in general use, such as mica or metal diaphragms. Thus the relatively stiff portion is included in a readily flexible disc of material which is mainly non-resilient by comparison with the relatively stiit portion or with diaphragms in general use and results in a diaphragm which is totally different in effect to one in which a stiifener is applied to material having the usual de gree of resilience such as is possessed by mica or metal sheet for example. A diaphragm according to the present invention leaves the relatively stiff radial strip free to vibrate readily with but little restraint imposed upon it from the surrounding portion by reason of the comparative non-resil iencc and flexibility of the latter.

Preferably the relatively stiff portion or strip is rendered more rigid in the region that the inner end of the stylus bar and that part of the diaphragm to which it is connected shall both be enabled to move over approximately the same are without material restraint during the oscillation of the stylus bar while sound recording or sound reproducing.

It will be appreciated that the stylus bar will be similarly connected to the diaphragms illustrated in Figures 5 and 6 and 8 to 12, respectively, but, for the sake of clearness, the stylus bar has been omitted from the drawings.

Figure 5 shows a method of constructing a diaphragm having characteristics similar to those above described and in this case a disc of mica or other material 28 is weak ened or rendered more flexible by perforations 29 at all parts of it except the central portion 22. which. constitutes substantially the equivalent of the relatively stifi' portions 22 in the foregoing examples. In this case the disc 28 will be covered on one or on both sides with thin paper as in the first described example, in order to close the perforations.

In Figures 10-12 is illustrated a still further modification of diaphragm construction in which a disc 30, conveniently of thin celluloid, is corrugated with the circular marginal corrugation 31 and cross corrugations 32 and 33 in order to render it as yieldable as possible. The relatively stifi' portion is formed by cementing one or more pieces of paper or other suitable material on one or both sides of the diaphragm as shown at 22, and in order to render that edge of the stiffened portion, where the stylus-bar is connected to it, more rigid than the remainder of it, a cross-strip of paper or celluloid or other material 34 is cemented over one of the strips 22. The diaphragm may obviously be corrugated in. other manners than that shown in the drawings in order to give it the desired additional flexibility.

In this, and in the other constructions in which celluloid is employed as the flexible portion of the diaphragm and paper is used as the sti'fljcncr it is found to be advantageous to utilize a solution of celluloid in amylacetate or other celluloid solvent as the adhesive for securing the paper strips to the celluloid ot' the diaphragm. The paper should be a IllOOlll surfaced paper, )articu larly that e of it which is to adhere to the celluloid diaphragm.

It is preferred to construct the stiflj'ened portion 22 oi the diaphragm of such stiltness that, with rapid Vibrations such. as are associated with. treble notes, vibration is imparted mainly to the region in which the stylus-bar is connected but with the less rapid vibrations, for example, of the bass notes, the Whole of the relatively stiff portion may be vibrated and possibly moved bodily. The flexibility of the portion of the diaphragm surrounding the stiffer portion should be such as to permit these vibrations with as little tendency to resist or interfere with them as possible.

It will be obvious that whereas the stylusbar oscillates about an axis generally outside the sound-box casing, the stiffer 901'- tion 2- will tend to vibrate or oscillate a .iout an axis nearer to the point of connection of the stylus-bar with the diaphragm. Thus, at this point of connection, the inner end of the stylus-bar tends to move along an arc of greater radius than does the equivalent pointof the stiffer portion of the diaphragm, with the result that in course of time the connection between the stylus-bar and the diaphragm runs the risk of be coming damaged or loosened. In Figures 8 and 9 a construction is illustrated which tends to mitigate this objection and for this purpose the flexible portion or disc 27, for example of celluloid, has secured, on one face of it, a stiifening portion 22, for example of paper, as in the example shown in Figure 6. On the other face of the disc 27 is a second strip 35, conveniently also of paper, whose inner end overlaps the inner end of the portion 22. The stiffness of the parts 22 and 35 is so chosen that under the influence of the vibration from the stylusbar the two portions mutually foo-act in such a manner as to cause the point 26 of the composite diaphragm to move naturally along the same, or approximately the same, are as that along which the inner end of the stylus-bar will move. At the same time the overlapping portions of the parts 22 and afford the equivalent of the cross-strip 34 in Figure 12, which not only tends to strengthen the diaphragm in the region of its connection with the stylus-bar, but also tends to prevent buckling of the stiffened portions 22 and 35. The effect of this is to assist the strip to flex about lines at rightangles to the stylus-bar and parallel with the plane of the diaphragm and to tend to limit buckling to a bending only about the centre line indicated, for example. by the section-line 9 9 of Figure 8 and about an axis at right-angles thereto.

In the constructions illustrated in Figures (3 to 11. materials of the following dimensions are found to give good results.

The diameter of the diaphragm disc exposed within the opening of the sound-box is ap 'iroximately 1 5; inches and the celluloid from which the portion 27 or 30 is formed is a 'iproximately fifteen tl'iousandths of an inch thick.

The strip 22, of tough paper, is approximately nine thousandths of an inch, thick and the thickness of the strip (also of tough paper) Figures 8 and 9, is approximately eight thousandths ofan inch.

9. For a sound box of the type described, a diaphragm comprising a sheet of flexible, substantially non-resilient material formed with a relatively stifl' portion constituting a radial strip extending approximately from one margin of the diaphragm to the center thereof and formed for connection with a stylus bar without the interposition of a swinging link, the connection between the stylus bar and the relatively stilt portion bein at or near an edge of the latter which is a jacent to the center of the diaphragm, substantially as described.

10. For a sound box of the type described, a diaphragm comprising a sheet of flexible and having a relatively stifi' portion constituting a substantially radial strip extending ap proximately from the margin of the diaphragm to the center thereof and formed to connect With a stylus bar at or near an edge of said strip which is adjacent to the center of the diaphragm, and a second radial stiffening strip applied to the dia- 25 plu'agm and overlapping at least a portion substantially nonresilient material,

of the first mentioned strip, substantially as described.

11. For a sound box of the type described,

a diaphragm comprising a sheet of flexible and substantially non-resilicnt material having a relatively stitl' portion constituting a substantially radial strip which extends ai iproximately from the margin of the diaphragm to the center thereof and formed to connect with a stylus bar at or near an d strip which is adjacent to the center of the di iragm, and a second radial. stiffening st ip applied to the dia phragm and forming with said first portion a relatively stiii portion eccentrically positioned with respect to the center of the diaphragm, substantially as described.

In testimony whereof we have si ned our names to this specification in the presence of two subscribing Witnesses.

WILLIAMZ ERNEST CLIFTON.

JOHN STURTON ElVAR-T. Witnesses:

CHAS. L. NoRnoN,

ALFRED HoRNnR.

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