US1901202A

US1901202A - Electrostatic loud-speaker

Info

Publication number: US1901202A
Application number: US359235A
Authority: US
Inventors: Adolph A Thomas
Original assignee: Individual
Current assignee: Individual
Priority date: 1929-04-30
Filing date: 1929-04-30
Publication date: 1933-03-14
Anticipated expiration: 1950-03-14

Description

March 14, 1933. A. A. THOMAS ELECTROSTATIG LOUD SPEAKER Filed April 30, 1929' AHA INVENTOR Patented Mar. 14, 1933 PATENT! OFFICE .ADOLPH A. THOMAS, F NEW YORK, N. Y.

ELEc'rRos'rATIc V.appliamon mea April so,

My invention is for a novel construction of electric loudspeaker apparatus particularly adapted for vtalking movies to improve the reproduction of sound. As far as I am aware,

the only type of loudspeaker 'used at the present time in theaters exhibiting talking ymovies is the old-fashioned horn. Usually more than one horn is used, these horns being arranged in proximity to the screen. Since the horns must be concealed from the audience, they have to be covered in some way and that tends to muiiie the sound. But aside from that, owing to the large volume of sound required in theaters, the loudspeaker horns must be of great size, and it is a matter of experience that big horns with necessarily long sound passages give a rumbling unnatural reproduction, often lacking in clearness. In some talking movies it is sometimes impossi- '20 ble to distinguish between mens voices and womens voices, and between the various instruments of an orchestra. Unless the speech and music (particularly the dialogue) accompanying a motion picture are reproduced 2- in a clear and natural manner, an audience finds no enjoyment in thestory of the picture. There are, indeed, many people who object to talking movies on that account and avoid them.

Itis the purpose of this invention to improve the reproduction of soundin talking movies by the use of electrostatic loudspeakers arranged close to the screen and directly Open to the auditorium. Where the screen 5 is on a curtain adapted to be raised and lowered, as in large theaters having a stage, I

support one or more condenser speakers on the curtain itself in permanent relation to the screen. This arrangement has the practical advantage that the loudspeakers do not have to be handled at all, for they move out of the way when the screen is raised. In one embodiment of my invention, I use several condenser speakers surrounding the screen yand constructed to accentuate different bands of frequencies.l This enables me to reproduce the entire musical scale with substantially uniform efficiency and fidelity. Owing .to their flat construction, these loudspeakers LOUD-SPEAKER,

1929. serial No. 359,235.

on an exaggerated scale to show the mountl in of certain parts inthe structure of Fig. 2;

ig. 5 is-a partial front view of the loudspeaker construction illustrated in Figs. 2-4; and

Fig. 6 shows a side section of a modified 79|.

form of condenser speaker in which the vibratory electrode is behind aperforated section of the curtain.

A theater curtain 10 carries a motion picture screen 12 of any approved construction. 75 These screens are usually an integral part of the curtain itself, but sometimes they consist of special material attached to the curtain., The particular construction of screen 12 and its mounting on c'urtain 10 are imma- 80 terial in reference to the scope of my invention. The curtain 10 carries loudspeaker mechanism of the electrostatic type adjacent to screen 12. In the articular embodiment illustrated in Fig. 1, this loudspeaker mech- S5 anism comprises a plurality of condenser I speakers, marked A, B and C, surrounding the screen 12. These loudspeaker units have vibratory electrodes of different size to accentuate correspondingly dierent bands of frequencies. For example, the three upper speaker units A have diaphragms for accentuating high notes, the two lower speakers B are adapted to emphasize the middle register, and the two side speakers C, which are the largest, are intended to bring out the low notes. In this way, all the frequencies are brought out with substantially uniform eiiciency and fidelity over the entire musical scale wthn practical limits.

In the broad aspect of my invention, the condenser speakers may be of any approved construction, and by way of example I have illustrated a simple form of speaker which is so flat that its presence on the curtain would hardly be noticed by the audience. Referring to Figs. 2-5, there is a rigid condenser plate 13 and a. vibratory electrode 14, which is a tensioned sheet adapted to operate as a loudspeaking diaphragm. The plate 13 is a rectangular piece of sheet metal, preferably aluminum, which is light and stiff, altho'ugh other metals may be used, such as brass, iron,

'- and the like. In the present instance, the

diaphragm 14 is mounted directly on the fixed plate 13 by a frame 15, which may be of insulating material or a light strip of metal. The rigid plate 13 is provided with ribs 16 which serve to tension the diaphragm 14 and at the same time hold it spaced from the fixed electrode 13. The Yribs 16 may be arranged in the outline of a rect-angle to engage the tensioned diaphragm sheet all around, or they may be provided at only two opposite edges of plate 13, in which case the diaphragm will be entirely free at two edges.

The diaphragm 14 may be a thin sheet of flexible metal, such as duralumin. steel, nickel, invar (an alloy of steel and nickel), brass, and so on; or it may consist of an insulating sheet, like fabric, rubber, Celluloid, etc., covered on the outside with a coating or other suitable metallic surface. If the diaphragm sheet 14 is of met-al, it will have to be insulated from the metal plate 13 in any practical way. The space 17 between the

condenser elements

13 and 14 may be filled with elastic dielectric material adapted to permit free and full vibration of the diaphragm. Screws 18 or other fastening devices hold the edge of diaphragm 14 clamped between the frame 15 1 and the outer Hanges 19 of plate 13. A second frame 20, preferably of insulating material, is mounted on the back of curtain 10 and holds the condenser speaker rigidly attached to the front side of the curtain. Screws or like vmembers 21 hold the frame 20 and condenser plate 13 rigidly connected on opposite sides of curtain 10. Two

binding posts

22 and 23 project from the rear frame 20 for conveniently connecting the

condenser elements

13 and 14 in a circuit of variable potential. The binding post- 22 is electrically connected to the fixed plate 13, while the binding post 23 is in metallic contact with diaphragm 14 by means of a screw or bolt 24. It is here assumed that the clamping frame 15 is of metal and in electrical contact with diaphragm 14 over a wide area.

In the modification of Fig. 6, the condenser speaker comprises a fixed plate 25 and a vibratory electrode 26, wh-ich constitutes a loudspeakingdiaphragm. What has been said about the diaphragm 14 of Figs. 2-5 may be considered applicable to diaphragm 26 without the need of repetition. The edge of diaphragm 26 is clamped between a pair of insulating frames 27 and 28, which are secured to the rigid plate 25 in any practical way, as by screws, bolts or rivets (not shown). In this construction the condenser unit is mounted on the back side of curtain 10 and is held in place by an insulating frame 29, which is arranged on the front side of the curtain and connected to the condenser unit by screws 30 or otherwise. The curtain 10 is perforated at 31 to permit free passage of sound into the open air.

It may be assumed that the specific constructions of condenser speaker above described are applicable toI all the units A, B and C of Fig. 1, although it is not essential in actual practice that the different speakers be constructed exactly alike. If the dia.- phragms are arranged on the front side of the curtain and directly exposed to view, they may be painted or covered with a material that harmonizes with the design of the supporting curtain 10, so that the presence of the speakers will not be noticed by the audience. Leastwise, the speakers will be regarded as some kind of decoration around the screen 12. Although I have shown seven loudspeaker units in Fig. 1, my invention is not limited to any particular number of speakers nor to any precise arrangement thereof in relation to the screen. It is desirable to mount the speakers as closely to the screen as possible, so as to create the illusion that the sound is coming from the characters in the picture.

The curtain 10 also performs the useful function of an acoustic baiiie which prevents the sound generated by the speaker units from passing back of the curtain, so that all sound waves are projected forwardlyl toward the audience. Since the

diaphragms

14 and 26 are directly open to the auditorium, the reproduction is clear and natural. It is assumed, of course, that the loudspeakers are properly connected in circuit. I have notconsidered it necessary to show or describe any circuit connections, because they will be understood by experts in this art. In large theaters having a stage on which the settings are frequently changed, the curtain 10 will be mounted for raising and lowering, carrying with it the screen 12 and the loudspeakers A, B and C. The latter are therefore always in proper relation to the screen without attention by the stage hands. The curtain 10 may also be a fixed support for the screen and the condenser speakers.

Although I have shown and described certain specific constructions, I want it understood that my invention is not limited to the details set forth. It is to be expected that changes and modifications will occur to those scope of the invention as defined in the appended claims.

I claim as my invention:

1. The combination of a motion picture screen and a plurality of electrostatic loudspeakers arranged around-said screen, said loudspeakers being flat structures mounted substantially parallel with said screen and having different natural frequencies to accentuate the entire musical scale within practical limits.

2. In'talking movie apparatus, a curtain having a motion icture screen, and an electrostatic loudspea er mounted on said curtain adjacent said screen, the vibratory electrode of said loudspeaker being open to the free air at the front of said curtain.

3. In talking movie apparatus, a curtain having a motion picture screen, and a plurality of electrostatic loudspeakers mounted on said curtain around said screen, said loudspeakers being arranged to throw the sound in a forward direction.

4. In talking movie apparatus, a curtain having a motion picture screen, and a plurality of electrostatic loudspeakers mounted on said curtain adj acentsaid screen, said loudspeakers having different natural frequencies to accentuate the entire musical scale within `practical limits. i 5. ln talking movie apparatus, a curtain having a motion picture screen, and an electrostatic loudspeaker mounted on said curtain adjacent the screen, said loudspeaker having a. diaphragm arranged behind the curtain which is perforated in front of the diaphragm to permit the projection of sound in a forward direction.

6. In talking movie apparatus, the combination of a sheet-like support having a p surface constructed to operate as a motion picture screen.) and an electrostatic loudspeaker mounted on said support near the screen, said louds 'ker comprlsing a condenser plate o substantially rectangular form provided with ribs `near the edge, sald plate extending beyond said ribs to form outer lflan l, a vibratory electrode mounted on sai plate in tensioned condition and held spaced from said plate by said ribs, fastening Vmeans for said Vvibratory electrode engaging said flanges, a frame on one side 'of said support for holding said condenser unit to the other side of said support, and fastening devices engaging said frame and unit and through saidsheetis rigidly mounted on said support.

7 In talking movie apparatus, the combination of a sheet-like support having a surface constructed to operate as a motion picture screen, a at electrostatic loudspeaker unit mounted on the rear side of said support near the screen, said support in front of said loudspeaker unit being pervious to the paswhereby said loudspeaker unit un1t.

8. In talking movie apparatus, the combination of a sheet-like support having a surface constructed to operate as a motlon picture screen, a iiat electrostatic loudspeaker unit mounted on one side of said support near the screen., a member on the other side of said support, and fastening means passing through said member and unit for securing the latter to said support. v

9. The combination of a theater curtain, a motion picture screen on said curtain, and electrostatic loudspeaker mechanism mounted on said curtain near said screen and arranged to throw the sound forward, said mechanism being surrounded by the curtain which thereby acts as an acoustic bale to l direct sound waves forward.

10. An upright fiat support having a portion constructed to operate as a motion picture screen, and a plurality of electrostatic loudspeaker units mounted on said support t adjacent said screen and arranged to throw the sound forward, said loudspeaker units having different natural frequencies to accentuate the entire musical scale withinpractical limits.