US1846937A

US1846937A - Diaphragm for loud speakers

Info

Publication number: US1846937A
Application number: US451172A
Authority: US
Inventors: Alda V Bedford
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1930-05-09
Filing date: 1930-05-09
Publication date: 1932-02-23
Anticipated expiration: 1949-02-23
Also published as: GB387995A

Description

Feb. 23, 1932.

A. v. BEDFORD 1,846,937

DIAPHRAGM FOR LOUD SPEAKERS Filed May 9. 1950 Aida Bedford,

a jmwaw His Attorhqg.

Patented Feb. 23, 1932 UNlTED STATES PATENT OFFICE 'ALDA V. BEDFORD, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC OOMPANY, A CORPORATION OF NEW YORK DIAPHRAGM FOR LOUDSPEAKERS Application filed Kay 9, 1980. Serial No. 451,172.

of sound over a wide range of frequency.

Difiiculties have been encountered hereto-v fore in the use of large diameter diaphragms of the cone type arranged to be driven as aunit due to the tendency of portions of the diaphragm to respond to vibrations corresponding to the natural vibration period of such portions and to affect adversely the vibration of portions adjacent thereto. In accordance with the present invention these difficult-ies are avoided by the provision of a multiple diaphragm structure which comprises a plurality of conical sections, adjacent sections being coupled by a member or medium which is essentially dampin in nature. Driving force is applied preferably to that one of the conical sections which is of the smallest effective diameter and the force is thence transmitted to successive sections through coupling members constituted by the damping members or medium and interposed between adjacent sections.

My invention will be better understood by reference to the following description when 'considered in connection with the accompanyiug drawings and its scope will be pointed out in the appended claims.

Referring to the drawings, Figs. 1 and 2 are sectional and plan views respectively of a sound producing device such as a loud speaker comprising a diaphragm embodying the invention, and Fig. 3 is a diagram illustrating the operation of the diaphragm.

In Figs. 1 and 2 is illustrated a sound producing device or loud speaker comprising a cone diaphragm connected at its outer edge to a ring 11 of yielding material such as leather clamped between mounting rings 12 and near its apex to a magnet pole 13- by means of a. spider member'lel and stud 15.

The diaphragm is driven by a coil 16 connected thereto near the apex thereof and arranged to vibrate in the space between the magnet poles 13. The diaphragm is divided into a plurality of sections, as cone 17' and frustrums of

cones

18 and 19. In accordance with the invention these sections are coupled at their adjacent edges by

members

20, 21 which operate as damping elements between the sections. In the present embodiment of the invention.,-20 and 21 are ring shaped members cemented or otherwise fastened to adj acent sections of the diaphragm and formed of or comprising a material of high viscosity or one having a high damping coefficient and which may at the same time be elastic, such as flexible succinate resin.

The operation of the multiple cone diaphragm comprising the coupling members formed of dumping material as above described will best he understood by reference to the electrical diagram illustrated in Fig. 3. In this figure inductances Ms and M1 correspond rcspectively to the mass of adjacent diaphragm sections, for example to that of cone 17 and of" conical section 18, and resistance R to the damping coupling constant of the member 20. whichconnects these sections. Further, the "oltage E corresponds to the force applied to the diaphragm and the resulting current in Ms and M1 corresponds to motion of adjacent diaphragm sections, as 17 and 18. Assuming that the constants of the circuit shown in Fig. 3 are such that at a given intermediate frequency the impedance of M1 is equal to R, then it will be seen that for low frequencies, or frequencies considerably lessthan the given intermediate frequency, substantially the 'same current will flow in Me and M1. Since current in M8 and M1 corresponds to motion of diaphragm sections 17 and 18, therefore, if driving force of low frequency is applied to the diaphragm 10 the adjacent conical sect-ions 17 and 18 partake of thesame motion, or move substantially as one. At high frequencies in' the circuit of Fig. however, R will act as a shunt to M1 due to the greater impedance of this branch of the circuit at high frequencies and therefore the current flowing through Ms will be greater than that flowing through M1. For the corresponding case of the diaphragm, if driving force of high frequency is applied to the diaphragm the motion of the smaller conical section 17 represented by Ms, will be greater'than that of section 18, represented by M1. At high frequencies, therefore, section 17 will vibratestrongly, but owing to the damping action of coupling member 20 the larger conical section 18 will not vibrate appreciably. 7

It will be seen from the above description that the damping members forming the coupling means between the diaphragm sections so operate that at low fre uencies the force impressed on the section 0 smallest mass is transmitted to the Whole diaphragm, and as the frequency of the impressed force rises phragm comprisin a plurality of conical sections of different e ective diameters, coupling means for said sections comprising members having a high damping coefficient, and means connected. to the conical section of smallest effective diameter for actuating said diaphragm. v I e I In Witness whereof, I have hereto hand this 8th day of May, 1930.

ALDA V. BEDFORD.

set my fewer sections respond, until, at high fre quencies, only the section of smallest diameter responds. By reason of this action of the coupling means it is possible to prevent any section of the diaphragm from breaking up and vibrating appreciably at frequencies corresponding to natural vibration periods of portions of the sections, since. the section of smallest area may be constructed of such stiffness as'to vibrate only as a single unit even at high frequencies, and since the successively larger sections may be sufficiently stifl' to vibrate as single units only at those frequencies low enough for each section to receive appreciable driving force through the damping coupling. j

Further, since in the diaphragm described herein, the sound generating areas ma be of relatively small diameter compare to a sound Wave length even at very high frequencies, a loud speaker incorporating a diaphragm in accordance with the invention approximates the condition of a point source of sound, thus tending to generate a spherical sound wave and to simplify the interference pattern.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A diaphragm comprising a plurality of sections of successively larger area, and coupling means for said sections comprising clamping members connected to adjacent sec- 7 tions.

2. In a diaphragm, a plurality ,of conical one of said sections, said coupling means being arranged to transmit said force from one of said sections to'the others thereof in succession.

5. In a sound producing device, a dia-