US1893049A - Sound producing device - Google Patents

Description

Jam. 3, 1933. c. M. BOUDETTE 1,893,049

SOUND PRODUCING DEVICE.

Filed Aug. 30, 1932 2 Sheets-Sheet l Jan. 3 W33 c. M. BOUDETTE 178937949 SOUND PRODUCING DEVICE Filed Aug. 30, 1952 2 Sheets-Sheet 2 lllllll \w I INVENTUR: I

Patented Jan. 3, I933 PTENT' UFFICE CLAYTON MI. BOUDETTE, F REVERE, MASSACHUSETTS SOUND PRODUCING: DEVICE Application filed. August 30, 1932. Serial No. 631,039.

In radio loud speakers of the electrodynamic type where the voice-current coil is disposed in the air gap between the core and pole-piece of a magnet, usually an electromagnet, it is desirable to reduce the radial length of such air gap to a minimum and it is essential that said diaphragm and the actuating coil attached thereto be accurately centered with respect to said core so that said coil 19 may have free and unrestricted longitudinal movement, and no transverse motion, in said gap.

This invention involves a novel coil-supporting means which, while permitting free 35 longitudinal movement of the voice current coil in the air gap, accurately centers said coil and prevents any transverse movement thereof, thereby eliminating all danger of contact between said coil and the magnet ele- 29 ments. By means of this improved centering device a much narrower air gap can be used than is possible with the coil-centering means heretofore employed and the diaphragm and voice coil are permanently and accurately centered and aligned with respect to the magnetic system.

The preferred form of centering device is a washer of thin flexible non-hydroscopic material such as celluloid, qmetal, bakelite, non- 30 porous paper and the like which may be provided with corrugations, either concentric or spiral, or of any other suitable configuration to increase the flexibility thereof longitudinally without unduly reducing the lateral stiffness of the same. The voice-coil supporting-cylinder preferably projects through the central aperture of the centering washer and is cemented to the latter and the apex portion of the diaphragm, if the latter be of the conical type, with the result that the washer acts as a diaphragm-supporting means, as well as a means for centering and aligning the voice coil and diaphragm with respect to the magnetic structure.

In the drawings which accompany and form a part of this specification- Figure 1 is a plan view of a coil-centering washer embodying the present invention;

Fig. 2 is a section taken on the line 22 of Fig. 1;

Fig. 3 is a plan view of another form of centering washer;

Fig. 4 is a section taken on the line 4-4 of Fig. 2;

Fig. 5 is a longitudinal central section of a radio loud speaker provided with the coilcentering diaphragm-supporting washer shown in Fig. 1.

In the particular drawings selected for more fully disclosing the principle of my invention and which are to be considered as illustrative merely and not as restrictive, 10 is a washer formed of thin flexible non-porous material, such for example, as celluloid and provided with concentric corrugations 11 between the peripheral portion 12 and the cen tral aperture 13. The corrugated portion of the apertured disc or washer between the support for the peripheral portion thereof and said central aperture must have such radial to length as will permit of sufficient longitudinal movement of said disc and the parts thereto attached to effect the faithful reproduction of low notes. In the present instance, as shown in the accompanying drawings which are full size, except that the thickness of the washer is greatly exaggerated for clearness of illustration, the ratio of the diameter of the free or vibrating portion of the disc, i. e., the portion thereof within the inner periphery of said support, to the diameter of said central aperture is 2% to 1, approximately, and the ratio of the radial length of the corrugated portion of said disc to the thickness of the disc is approximately 250 to 1. I do not, 55 however, limit myself to such ratios, the requirement being that the amplitude of range of vibration of the disc must be relatively large if low notes are to be reproduced with fidelity. By the loud speaker shown in the drawings, the lowest notes of the musical scale are reproduced faithfully because a range of vibration of 4 inch can be obtained without breaking or cracking the disc. It will be understood of course that I do not limit my- 95 self to a loud speaker of the exact size shown in the drawings and that the principle underlying the speaker herein specifically disclosed is applicable to speakers larger and smaller than the one illustrated in the drawings. 1W

I am aware that diaphragms with corruated peripheral portions have been proposed or loud speakers of the horn type, but in such case the radial length of the corrugated 5 portion thereof must be small compared to the diameter of the diaphragm to ensure the lateral stiffness necessary for preventing the rocking of the diaphragm, with the result that the vibration range of such diaphra ms is much too small for the faithful reproduction of low notes if said diaphragm were used in a speaker of the cone type.

Inasumch as the corrugation of a coil-centering disc reduces the lateral stifl'ness thereof and as such disc must have sufficient lateral stiffness to permit the use of an extremely narrow air gap, it follows that the radial length of the corrugated portion of the disc must necessarily be a compromise between Such radial length must be sufficiently great toimpart to the disc such elasticity as will permit, other things being equal, of a relatively large vibratlon range, and yet not so great as to reduce the lateral stiflness of the disc to the degree that will prevent the use of a narrow air gap with very small clearance between the voice coil and the side of said g It will be obvious that if a voice coil of larger diameter than that shown in the drawings is used, the ratio above-mentioned would be smaller than 2% to 1.

It will be obvious also that the radial length of the corrugated portion of the disc, for a. given range of vibration, is dependent, other things being equal, upon the thickness of the disc, and further, that such radial length for a given range of vibration and given thickness of disc is dependent upon the size and. weight of the cone. For; example, if the thickness of the disc be reduced, the radial length of the corrugated portion thereof also may be diminished, and if the size or weight of the cone be augmented, such radial length may be reduced, and vice versa.

In view of the various factors entering into the determination of the radial length of the corrugated portion of the washer or disc, it is to be understood that I do not limit myself to any particular ratio of diameter of the free portion of the discto diameter of the central aperture thereof, or to any particular ratio of radial length to thickness of disc, and that 55 I desire to cover by the appended claims a loud speaker of the cone type in which the radial length of the-corrugated portion of the centering disc is sufiiciently great to permit of the range of vibration required, other 60 things being equal, for the faithful reproduction of low notes without sacrificing the lateral stiffness necessary to permit the use of an extremely narrow air gap. If celluloid is employed for the washer, the corrugations conveniently may be formed by heating the longitudinal flexibility and lateral stiflness.

disc and pressing the corrugations thereinto by a die.

In Fig. 3 the disc is provided with concentric corrugations 14. It will be understood that as the purpose of the corrugations is to increase the flexibility of the washer longitudinally without unduly reducing the lateral stiffness thereof, such corrugations may be of any sha e or configuration that will effect the desi 'result.

Referring to Fig. 5, the electromagnet 15 is provided with a core 16 and pole-piece 17, apertured to receive said core. The voicecurrent coil 18 is wound on the coil-supporting cylinder 19 and is disposed in the air gap between the core and pole-piece. The outer flange 20 of the diaphragm 21, herein shown as a cone, is flexibly supported by the flange 22 of the pan 23 secured to the magnet structure by bolts 24. The lower portion of said pan forms an annular support 25 for the outer peripheral portion of the centering washer which preferably is cemented to said annular support. Preferably a thin coating of cement is placed on the coil-supporting cylinder and the latter is then passed through the apex portion of the cone in order to secure these two elements together. The central aperture of the centering washer may be provided w1th a flange 26 inorder to facilitate the cementmg of said washer to the coil-supporting cylinder, which preferably is secured both to the diaphragm and washer. It will be understood of course that this invention is not limited to the particular means disclosed for securing the aforesaid elements together, inasmuch as many alternative means will readily occur to those skilled in the art for accomplishing this purpose.

It has been found'in practice that the use of a centering washer of the character described herein permits the permanent and accurate centering and aligning of the diaphragm and voice coil with respect to the magnet structure and makes possible a substantial reduction in the radial length of the air gap. The flexibility of the centering washer eflected by the corrugations is such that the voice coil has free and unimpeded movement longitudinally with respect to the air gap while lateral stiffness thereof is not reduced sufficiently to permit any transverse movement of said coil in said gap.

It will be obvious that various changes in structure and relationship may be made by those skilled in the art without departing from the scope of the invention as defined by the appended claims.-

I claim:'

1. A sound-producing device comprising in combination, a cone diaphragm flexibly supported at its base, an actuating coil secured to said diaphragm, a corrugated imperforate coil-centering diaphragm-supporting llt) thereof without unduly reducing the lateral stiffness of the same.

3. A sound-producing device comprising in combination, a cone diaphragm flexibly supported at its base, an actuating coil secured to said diaphragm, a coil-centering diaphragm-supporting disc of thin flexible ma- Lerial provided with concentric corrugations and a support for the peripheral portion of said disc, the corrugated portion of said disc having-sufficient radial length to permit of free longitudinal movement thereof withou unduly reducing the lateral stifl'ness of the same.

4. A sound-producing device com rising in combination, a cone diaphragm exibly supported at its base, an actuating coil secured to said diaphragm, a coil-centering diaphragm-supportlng disc of thin flexible material provided with spiral corrugations, and. a support for the peripheral ortionof said disc, the corrugated portion 0 said disc having sufficient radial length to permit of free longitudinal movement thereof without unduly reducing the lateral stiffness of the same.

5. In a sound-producing device having a diaphragm flexibly supported at its base and an actuating coil secured thereto, a corrugated imperforate coil-centering diaphra supporting disc of thin flexible non-hydi' scopic material, and a support for the peripheral portion of said disc, the corrugated ment thereof without unduly reducing the lateral stiflness of the same.

' 7. A sound-producing device com rising in combination, a cone diaphragm flexibly supported at its base, a magnet having a core and a pole-piece, a coil support, an actuating coil carried by said support, said coii bein disposed in the air gap pole-piece and c said core an ort being se cured to said diaphragm, a thin corrugated disc for centering said coil, said disc being of thin flexible material and having a central aperture for receiving said coil support, and a support for the peripheral ortion of said disc, the corrugated portion 0 said disc having suflicient radial length to permit of free longitudinal movement thereof without unduly reducing the lateral stiffness of the same.

8. A sound-producing device com rising in combination, a cone diaphragm exibly supported at its base, a coil support, an actuating coil carried by said support, a corrugated coil-centering disc formed of thin flexible material and provided with a central aperture, a support for the outer peripheral portion of said disc, said coil support passmg through said aperture and being secured to said diaphragm and to said disc, and a magnet having a core and a pole-piece, said coil being disposed in the air-gap between said core and pole-piece and the corrugated portion of said disc having sufiicient radial length to permit of free longitudinal movement thereof without unduly reducing the lateral stiffness of the same.

In testimony whereof I aflix my signature.

CLAYTON M. BOUDETTE.

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