US1434788A - Vibrating system - Google Patents

Description

J. P. MAXFIELD.

VIBRATING SYSTEM.

APPLICATION FILED AuG.2a, 1917.

1,434,788, v Patented Nov. 7, 1922.

\\\IIIII Ff? Patented Nov. 7, 1922.

UNITED STATES PATENT OFFICE.

JOSEPH P. MAXFIELD, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION OF NEW YORK.

VIBRATING SYSTEM.

Application led August 28, 1917. Serial No. 188,582.

7'0 Hui/1.0711 iti/may concern.'

Be it known that I, Josemi P. MAxFI'nLD, a. citizen of the United States, residing at Maplewood, in the county of Essex and State of New Jersey, have invented certain new and useful .Improvements in Vibrating Sys tems, of which the following is a full, clear, concise, and exact description.

This invention relates to i'liapliragms, and more particularly to phonographic diaphragiiis such as those used in phonographic recorders and reproducers.

The object of this invention is to provide ay diaphragm which will be more sensitive to a wider range of fiequeiicy than those hei'etofoi'e employed. A specific object is to' construct a diaphragm having both a low natural frequency and a. higli natural frequency.

Although this invention will'be hereinafter described in connection with a phonographic reproducer or sound box, it is not limited to such an application, but may be employed in connection with any suitable `sound recording, transmitting or receiving device in which a' vibrating member may he included.

It is well know in the art that a diaphragm clamped at its edges,l as in u sound box for a talking machine or in a telephone transmitter, for example, does not respond equally for all frequencies of vibration iinprcssed upon it, but for each diaphragm there is a frequency in the neighborhood of which there will be maximum response, and for other frequencies the response will be much less. The frequency for maximum response is generally known as the natural frequency of the diaphragm. The value. of this natural frequency for a diaphragm depends upon its elasticity or stiffness and mass, increasing with increase in elasticity, and decreasing with increase in mass. The amount of response for any given frequency depends upon the friction, effective mass and the elasticity of the vibrating system.

For frequencies near the natural period the response is governed mainly by the friction, being larger the smaller the friction;

above the natural period the effective. mass is the governing quantity, the response being larger the smaller the mass; while below the other hand, if the diaphragm has a low degree of elasticity and is of appreciable mass the low notes will be reproduced Well, to the detriment of the higher toiles.

rl`his invention embodies a diaphragm of such a character that it will reproduce etliciently notes of both low and high frequency. To accomplish this, the diaphragm is made non-uniform and capable of vibrating in two different ways. In the specific embodiment hereinafter described in detail, the diaphragm consists of a centra-l portion of a highly elastic material 'having a high natural fre( uency and an outer ortion composed of a flexible membrane. en such a diaphragm is clamped between suitable clamping arms and a stylus bar carrying the reproducing or recording needle is fastened to thecentral portion of the diaphragm and vibrations of low frequency are impressed on the diaphragm, the entire diaphragm will undergo displacements on account of the low natural frequency of the outer ortion. Of course, the natural frequency of vibration of the outer portion of the diaphragm is lowered somewhat by the addition of the mass of the central portion, and is also modified to sonic extent by the fact that the central portionis connected to the st lus bar. The central portion on account o its high natural frequency will not vibrate of itself, but will act asa plunger. When, however, the oscillations impressed on the diaphragm are of high frequency, the central portion, on account of its hioh natural fre ueiicy, vibrates readily, whi e there is fectively responds to both low and high frequencies, as well as those intermediate in value.

For the better understanding ofy this invention, reference is made to the accompanying drawings, in which Fig. 1 represents a cross-sectional view of this invention as embodied in a phonographic sound box; Fig; 2 illustrates the top view of a portionY of the same; and Fig. 3 is a cross-sectional view of a diaphragm.

ln the embodimentof this invention illustrated in Fig. '1, 4 is a sounding box suitably fastened to the frame or diaphragm holder 5. A flange 6 of the frame serves to clamp the diaphragm 7 between two rubber gaskets 8 and 9. Upon the frame 5 is mounted a bracket 12, which, by means of the knife edges 13 (see Fig. 2), supports a socket 14 adapted to receive a stylus needle. The stylus bar 17 is fastened at one end to the socket 14 and at the other end is fastened to the central portion df the diaphragm 7. Suitable tension on the stylus and diaphragm is obtained by the springs 18 (see Fig. 2). Diaphragm 7 has an outer portion 19 of flexible material and a central portion `20 of a highly elastic material. rlhe stylus bar 17 is shown attached to said central portion: lf we assume that the stylus needle is impressing vibrations of low frequency upon the diaphragm, the whole diaphragm will undergo displacements on account of the low natural frequency of the flexible material which composes the outer part of the diaphragm. The stiff central portion 20 will not vibrate of itself but will act merely as a plunger attached to the stylus bar 17. When, however, the impressed vibrations are high, the stiff central portion will of itself undergo vibrations on account of its high natural period, while the displacements of the remainder of the diaphra-gm`will be negligible. It has also been found, providing the stylus bar and the diaphragm are of minimum mass, that for vibrations of intermediate frequency 'between the two natural frequencies the diaphragm responds elliciently, although the response is not as great as for frequencies near one of the natural fre uencies.

ig. 2 shows more in detail the of the stylus bar to its supporting structure.

. The stylus bar 17 is shown to'have two arms 25 and 26, which are pivoted on two knife edges 13, 13. The two tensioning springs 18, 18 extend from the bracket 12 to the arms 25, 26. Since the stylus bar and its supporting arms are also part of the moving system, it is preferable that the eective mass of the stylus should be as small as possible, for otherwise, as stated previously, the response for frequencies on either side of the natural frequency would be inefficient. Itis, therefore, preferable that the stylus rel ation mames bar should be made of some light material such as aluminum.

All of the above structure, except that of the diaphragm and the light mass stylus bar, is well-known in the art and is described merely to enable the application of this invention to be more. readily presented.

Fig. 3 is a cross-sectional view of the diaphragm showing in detail its structure. 3() and 31 are two thin sheets of a flexible material, such as paper, cemented together near their outer edges. Between the two sheets, and suitably cemented together and to the paper sheets, are three discs 32, 33 and 34, of some suitable highly elastic material such as wood or steel, for example. lt is preferable that the dia-meter of these discs should be from one-third to five-sixths of the diameter of the sheets of paper, although the ratio may have any suitable value, depending upon the material composing the discs and the other vibrating parts. The discs shown are made of wood and have their grains crossed in such a manner that warping is prevented. Any number of discs may be used in order to obtain the desired stiffness; in the case of metallic discs only one would be necessary. It has been found convenient to use two sheets of paper and to cement the discs in between the sheets, but such an arrangement is not essential, as the discs may be cemented on the outside, in which case only one sheet of paper could be used. The membranes between which the discs are suspended may be of any suitable flexible material such as paper, oiled silk, or parchment. It is readily seen that such a diaphragm is not limited to lthe supporting structure illustrated in Fig. 1, as it may be used in connection with any sound box desired, or in connection with any suitable structure in which a vibrating.- member is employed.

What is claimed is:

1. A diaphragm. comprising a plurality of wooden discs of approximately the same diameter and cemented together, a thin sheet of paper cemented to each side of said discs, said sheets extending beyond the edges of said discs and having their extending portions cemented together, the part of said diaphragm within the perimeter of said discs having a natural frequency of vibration corresponding to a high musical note.

2. A diaphragm comprising two flexible membranes cemented together, a disc of small mass suspended between said membranes, a part of said membranes extending beyond the perimeter of said disc and having a natural period corresponding to a low musical note and the portion of said diaphragm lying within the perimeter of said d isc having a natural frequency of vibration corresponding to a high musical note,

whereby said portion is adapted to vibrate within itself enbeenntieuy independent ef the remainder of Said diaphragm for vibrations of the natural frequency of said portion.

3. A diaphragm comprising two thin `sheets of paper cemented together, and a plurality of wooden discs between said sheets at their centralfportion adapted to act as a plunger when the whole diaphragm is vibrating, the part of said diaphragm within the perimeter of said discs having a natural frequency of vibration corresponding toa high musical note,

4. A diaphragm having a natural period corresponding to a. low musical note and comprising a central portion of small mass and a flexible portion, said central portion having a natural period corresponding to a higher musical note and comprising a disc of stili', highly elastic material, and saidk flexible portion being of larger diameter than said disc and forming a flexible mounting for said disc, 3

5. A vibratory system comprising a stylus bar and a diaphragm, the stylus bar and the diaphragm as a whole having a natural period corresponding to a low musical frequency, said diaphragm comprisingacentral portion of small mass and a exible portion, said central portion having a'natural period corresponding to a higher musical frequency and com risin a disc of stiff, highly elastic materlal, said flexible portion being of larger diameter than said disc and forming a flexible mounting for said disc, the effective mass of the stylus bar and of the diaphragm each being small, whereby the system is highly responsive to musical frequencies other than saidtwo musical frequencies.

. 6. A vibratory system comprising a dia-- phragm and having a natural period corresponding to a low musical fre uency, said diaphragm comprising a centra portion of small mass and a exible portion, said central portion having a natural4 period corresponding to a higher musical frequency and comprising a dlsc of stiff, highly elastic -material, said flexible portion being of J OSEPH P. MAXFIELD.

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