US1747952A

US1747952A - Electrostatic loud-speaker

Info

Publication number: US1747952A
Application number: US328598A
Authority: US
Inventors: Reisz Eugen
Original assignee: Individual
Current assignee: Individual
Priority date: 1927-12-29
Filing date: 1928-12-26
Publication date: 1930-02-18
Anticipated expiration: 1947-02-18
Also published as: NL23896C

Description

Feb. 18, 1930. E.'REISZ ELECTROSTATIC LOUD SPEAKER Filed Dec. 26, 1928 AT Tm NYs UNITED s EUGEN BEISZ, BERLIN-DAHLEM, GERMANY ELECTROSTATIC LOUD-SPEAKER Application filed December 26, 1928, Serial No. 328,598, and in Germany December 29, 1927.

' This invention relates to electrostatic loud speakers and the like, and more particularly to electrostatic loud speakers of the kind in which a soft ductile membrane, provided duced by the loud speaker are no longer proportional to the applied electrical amplitudes and distortion consequently occurs.

According to this invention the rigid conductin late of an electrostatic loudspeaker of the 1nd referred to is formed with holes or perforations of such shape that, even with large amplitude vibrations, the electrostatic forces upon the membrane, and therefore the movement thereof, remain proportional to the applied electrical amplitudes.

The invention is illustrated in the accompanying drawings in which V Figure 1 shows the essential portions of a loud speaker in accordance with the sald 1nvention, I

Figures 2 and 3 are enlarged fragmentary views of a portion of the said loud speaker with its membrane in two different positions, while Figure 4 indicates diagrammatically the chief positions of the membrane durlng its oscillations,

Referring to the drawings, a is a membrane, for example, of rubber, upon which is afiixed a thin layer 6 of a conducting ma terial, as, for example, carbon particles or a very thin metal foil. The membrane a is placed against a rigid metal plate 0 provided with holes 6 whose exterior walls f are curved parabolically as shown. The exact form of this curve, i. e.- the parabola, determines the distribution of the electrostatic field, and. the

/ into the positions shown at w and If the dimensions of the said curve Will clearly de pend upon the stiflness of the membrane a (taking into account, of course, the coating 6) and the value of the constant component of the electrostatic field, i. e. the value 5; of the bias field. This bias field, which isdue to the constant component of potential applied to the loud speaker, and the value of the rigidity of the portions a and I), determine the exact course of the line f. 6( It has been found, as a result of a large number of experiments, that for the desired result the curve f should be a parabola, in which stiffness of the membrane and electrostatic bias of the loud speaker are the varie5 ables. Obviously,vthe dielectric constant of the insulating material employed, i. e. of the membrane, will afiect the dimensions of the parabola, but since the experiments referred to have all been made with one and the same 7( insulating material as membrane, this consideration is not contained in the parabola equation.

It will be seen that when the membrane oscillates towards and away from the open- 72 ings e in the solid metal electrode 0 of the loud speaker, a large number of small separate membranes is, in effect, produced, the said small membranes being in the untensioned condition bounded by the line w 8( (Figure 4). If, now, tension is applied, the flexible member a with its conducting coating 6 approaches the metal electrode and takes up the position shown by the curve y. Under the effect of varying applied potentials (acoustic potentials) between the electrode 0 and the coating 12, the limiting curve moves to and fro, that is to say, the membrane moves exterior Walls of the openings 6 are of parabolic form, as indicated in Figure 4, then the electrostatic field between the electrode and coating 1) will remain the same during movements of the membrane, since the air spaces 9 between the said plate a and oscillating membrane remain the same. In this way the loud speaker operates satisfactorily even when the magnitude of the potential amplitudes is very large. 10

I claim:

1. In anelectrostatic acoustic device, a metallic plate having openings through the same, a soft ductile membrane, and a coating 5 of a conducting material on one side of said membrane, said membrane being arranged I with its uncoated side opposed to an adjacent side of said plate to produce a structure hav ing the characteristics of a condenser, the Walls of the said openings being shaped to substantially parabolic form toward that side of said plate opposed to the said membrane.

2. In an electrostatic loud speaker or the like, a rigidmetallic plate having openings through the same, a soft ductile membrane and a relatively thin coating of a conducting material on one side of said membrane, said membrane beingarranged with its uncoated side directly opposed tovan adjacent side of said plate to produce a'structure having the characteristics of a condenser, the Walls of the said openings toward the ends thereof at the side of said plate opposed by said membrane being shaped to substantially parabolic form. In testimony whereof I have signed my name to this specification.

EUGEN REISZ.