US3590169A

US3590169A - Electrostatic horn loudspeaker

Info

Publication number: US3590169A
Application number: US722107A
Authority: US
Inventors: Josef Merhaut
Original assignee: Tesla AS
Current assignee: Tesla AS
Priority date: 1968-04-01
Filing date: 1968-04-17
Publication date: 1971-06-29
Anticipated expiration: 1988-06-29
Also published as: NL6804424A; DE1762079A1; DE1762079B2; GB1212243A

Abstract

An electrostatic pressure loudspeaker with a diaphragm vibrating at the rhythm of a signal frequency actuated by electrostatic forces operating between the diaphragm and at least one back electrode. At least one side of the diaphragm is connected with a horn through the input cross section of the latter which is smaller than the active area of the diaphragm, the ratio being 1 : 5 to 1 : 15. The cross section of the horn increases gradually from the input side facing the diaphragm to the output side in accordance with a predetermined law. The back electrode is provided with openings forming the input part of the horn. The input part of the horn connected directly with the diaphragm and the back electrode has a constant cross section.

Description

United States atet [72] lnventor Josef Merhaut Prague. Czechoslovakia [21] Appl. No. 722,107 [22] Filed Apr. 17,1968 [45] Patented June 29, 1971 [731 Assignee Tesla, Narodni podnik Prague, Czechoslovakia [54] ELECTROSTATIC HORN LOUDSPEAKER 5 Claims, 2 Drawing Figs.

[52] U.S.Cl 179/111 [51] lnt. Cl H04r 1/30, H04r 19/02 [50] Field otSearch l8l/3l.l; 179/1 1 l [5 6] References Cited UNITED STATES PATENTS 3,084,229 4/1963 Selsted et a1 179/111 355.149 12/1886 Dolbear 179/111 OTHER REFERENCES LOUDSPEAKERS; o. A. Briggs, 195s, pgs. 220 224 LOUDSPEAKERS: Ev J. Jordan, 1963, pgs. 121- 123,

Primary Examiner-William C Cooper Assistant ExaminerThomas Li Kundert At!0rneyRichard Low ABSTRACT: An electrostatic pressure loudspeaker with a diaphragm vibrating at the rhythm ofa signal frequency actuated by electrostatic forces operating between the diaphragm and at least one back electrode. At least one side of the diaphragm is connected with a horn through the input cross section of the latter which is smaller than the active area of the diaphragm, the ratio being 1 5 to 1 15. The cross section of the horn increases gradually from the input side facing the diaphragm to the output side in accordance with a predetermined law. The back electrode is provided with openings forming the input part of the born. The input part of the horn connected directly with the diaphragm and the back electrode has a constant cross section.

ELECTROSTATIC HORN LOUDSPEAKER I BACKGROUND OF THE INVENTION l. Field of the Invention The invention relates to an electrostatic pressure loudspeaker the diaphragm of which vibrates at the rhythm of a signal frequency actuated by electrostatic forces operating between the diaphragm and at least one electrode.

2. Description of the Prior Art Loudspeakers based on the electrostatic principle are usually provided with a diaphragm made of a thin foil of metal or metallized synthetic material. They are also provided either with a single back electrode or, if constructed as a push-pull loudspeaker, with two back electrodes arranged symmetrically on both sides of the diaphragm. These back electrodes are provided with holes to allow the flow of an acoustic signal from the diaphragm into the external surrounding space with the aid of a horn member. However, in all hitherto known r=c-8- S,. where 5,. is the cross-sectional area of the horn input, the other symbols having the same meaning as already explained above. A sudden narrowing of the cross section loudspeakers of the above type the diaphragm radiates into I the surrounding space either directly or through holes in the back electrodes without any acoustical transformation between the diaphragm and the channeled electrode. In such an arrangement the medium in the surrounding space into which the loudspeaker radiates sound waves, responds to the diaphragm as a mechanical resistance satisfying the equation r m n' I the notation being:

S,,,efiective area of diaphragm c,,speed of sound in the medium into which the loudspeaker radiates 8-density of medium In addition to this active resistance the electrostatic loudspeaker also has a resistance r 2 representing losses due to viscous friction, a reactance mm where m denotes the diaphragm mass and w is an angular frequency, and finally a compliance reactance c=l/mc SUMMARY OF THE INVENTION It is a general object of the invention to improve the features and performance of an electrostatic loudspeaker.

active area of the diaphragm lies-within the range of 1.5 to 1:5.

The cross section of the horn increases gradually from the input side facing the diaphragm to the output from which sound of the loudspeaker enters the surrounding medium, the increase being in accordance with an exponential function.

At least one electrode is provided with channels or waveguides interconnecting the diaphragm with the input part of the horn. The channels or waveguides Have a constant cross section.

According to another feature of the invention the inner back electrode of the loudspeaker is provided with openings forming the input part of the loudspeaker.

Still another feature of the invention resides in the fact that the input part of the horn connected directly with the diaphragm and the inner back electrode has a constant cross section.

The mechanical resistance in the input of a horn, such as employed in the invention, at a frequency j fl,,f being a certain critical frequency of the horn, is given by the expression between the diaphragm with an area S, and the horn input cross-sectional area 5., S, being k times larger than 5,, causes acoustical transformation of the mechanical resistance r into a value r wherein r is k times'larger than r. Consequently, the active resistance r of the-diaphragm is It is obvious that in the new arrangement with the horn the radiation resistance r is k times larger than in hitherto known loudspeakers radiating directly into the surrounding medium.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects of the invention and its various features and advantages will be best understood from the following specification to be read in conjunction with the accompanying drawing illustrating two preferred examples of the invention. In the drawing:

FIG. 1 illustrates a mechanical network of a loudspeaker system; and

FIG. 2 illustrates a push-pull system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more particularly 'to FIG. 1, the notation is as FIG. 2 shows cross section of a push-pull system in which one of the back electrodes forms also the input of the horn. This arrangement is particularly advantageous.

FIG. 2 shows the cross section of a push-pull system in which 1 denotes a diaphragm of thin metallic foil or metallized synthetic material. An outer back electrode 2 and an inner back electrode straddle the diaphragm l and are spaced from it. The inner electrode is formed having a plurality of waveguide channels or ducts 4 of constant cross section s,.. Mounted about the free side of the inner electrode 3 is the input portion (shown in cross section) of a horn.

As will be apparent, the sidewalls of the loudspeaker are flat and parallel toeach other and the horn 6, as illustrated, is of the exponential type. The inner electrode is formed by a plurality of wedge-shaped members located between the sides of the loudspeaker and separated by the constant cross sectioned channels 4, which connect the diaphragm 2 to the input portion 5 of the horn. Extending between the wedge members of the inner electrode 3 and the outer electrode 2 are spacer members 7 which extend through the diaphragm 2 and maintain it spaced from both electrodes This arrangement provides a stable, well-constructed loudspeaker having component parts which are easily manufactured and assembled.

The sum of all the cross-sectional areas of the channels 4 is equal to the cross section of the input 5 of the horn. The input 5 -of the horn is also smaller than the active area of the diaphragm l. The ratio between the area of the input 5 of horn 6 and the area of diaphragm 2 lies between 1:5 and 1:5. The cross section of horn 6 increases gradually from the input side facing diaphragm 1 to the output side from which the loudspeaker sound leaves the horn. This increase or widening follows a predetermined law or rule, for example in accordance with an exponential function.

The invention makes use of holes arranged in the inner back electrode 3 which perform as the input pan of the horn.

It is known that the channels 4 of constant cross section behave at a frequency j f,, as a plain transmission line which does not change the mechanical resistance or impedance of the horn input.

The arrangement of an electrostatic pressure loudspeaker provides improved loudspeaker features and performance since the increase of the resistance increases also the efficiency and widens the linear part of the frequency characteristic.

The horn arrangement shown in FIG. 2 is particularly convenient because of the waveguides created by the channels in the inner electrode. it is provided with an input having a constant cross section which can be produced in a very simple manner.

lclaim:

1. An electrostatic pressure loudspeaker comprising at least one electrode adapted to respond to an input signal to create an electrostatic force, a diaphragm spaced from one side of electrode and responsive to said electrostatic force to vibrate at a frequency of the input signal, a horn arranged on the other side of said electrode, said one electrode comprising a plurality of spaced wedgelike members, the spaces between said wedge members comprising waveguide channels extending between said diaphragm and said input section of said horn, said horn having an input section communicating with said diaphragm the cross section of which is smaller than the active area of said diaphragm.

2. The loudspeaker according to claim 1 including a second electrode spaced from the diaphragm on the opposite side thereof and cooperating with said one electrode to create an electrostatic force therebetween.

3. The loudspeaker as claimed in claim 2, wherein the ratio between the cross section area of the input section of said horn and the active area of said diaphragm is 1:5 to 1:15.

4. The loudspeaker according to claim 1, wherein the total cross-sectional area of said waveguide channels is equal to the cross-sectional area of said input section.

I 5. The loudspeaker according to claim 2 including spacer members extending between said electrodes and through said diaphragm to support and sectionalize said diaphragm.

Claims

5. The loudspeaker according to claim 2 including spacer members extending between said electrodes and through said diaphragm to support and sectionalize said diaphragm.