US2986228A

US2986228A - Miniature reverberation chamber system

Info

Publication number: US2986228A
Application number: US657940A
Authority: US
Inventors: Rettinger Michael; Jr Carl N Shipman
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1957-05-08
Filing date: 1957-05-08
Publication date: 1961-05-30
Anticipated expiration: 1978-05-30

Description

y 30, 1961 M. RETTINGER ETAL 2,986,228

MINIATURE REVERBERATION CHAMBER SYSTEM 4 Sheets-Sheet 1 Filed May 8, 1957 v rbkllllllllll r Pr||||ll|||| a I lll. IIIIIIII/ INVENTORS. MICHAEL RETTINGER a CARL u. SHIPMAN ATTORNEY 4 Sheets-Sheet 2 5 f f W W M. RETTINGER ETAL MINIATURE REVERBERATION CHAMBER SYSTEM May 30, 1961 Filed May 8, 1957 l r v:

INVENTORS. MICHAEL RETTINOER G N. SHIPIAN ATTORNEY M. RETTINGER ET AL 2,986,228 MINIATURE REVERBERATION CHAMBER SYSTEM May 30, 1961 Filed May 8, 1957 4 Sheets-Sheet 3 C I X4 I -25 Q t I: I g f 5 a 2 ,2! Q Z6 Q 30 I ll i 7 q M INVENTORS. MICHAEL RETTINGER a 4 CARL u. smpmm BY ATTORNE 7.

y 1961 M. RETTINGER ETAL 2,986,228

MINIATURE REVERBERATION CHAMBER SYSTEM Filed May 8, 1957 4 Sheets-Sheet 4 INVENTORS.

MICHAEL RETTINOER l CARL N. SHIPMAN ATTORNEY United States Patent MINIATURE REVERBERATION CHAMBER SYSTEM Michael Rettinger, Encino, and Carl N. Shipman, Jr.,

Rivera, Calif., assignors to Radio Corporaticn of America, a corporation of Delaware Filed May 8, 1957, Ser. No. 657,940

6 Claims. (Cl. 181-.5)

This invention relates to sound recording and reproducing systems, and particularly to that portion thereof whereby the characteristics of sound waves are modified before being recorded or reproduced.

Patent No. 2,431,962, of December 2, 1947, discloses and claims a reverberation chamber system in which the various wall sections of the chambers have no parallel surfaces, the chambers having a loudspeaker therein for generating sound waves and a microphone therein for detecting the waves. In this manner, various reverberation characteristics are obtainable, particularly by the use of a partition having a door between the diflerent size chambers. The chamber system of this patent, however, is of considerable size, thus requiring a large amount of space and expensive construction.

The present invention is directed to a reverberation chamber which will provide the same reverberation time as the patented chamber but which may be reduced in size from twenty-five to thirty times that of the patented chamber. Such a small chamber, therefore, is more economical to construct and may be placed in any normal size room wherever it is desired to modify sound waves being recorded or reproduced.

The principal feature which permits the large reduction in size of the chamber is the use of a heavy gas within the chamber plus the use of metal panels for the walls of the chamber. That is, for a gas having a density of approximately nine times that of air, a 27-fold reduction in chamber volume is possible. Several gases are operative, such as tungsten fluoride, vaporized mercury, and several types of Freon.

The reverberation chamber is enclosed within an outer chamber to prevent noise from being transmitted into the chamber as well as to prevent the reverberated sound from being transmitted into the room in which the entire unit is located. Bracing is provided between the opposite walls of the reverberation chamber to reduce excessive vibration of the walls. Furthermore, a 45-degree baffle is positioned along one corner of the chamber opposite the loudspeaker generating the sound waves to prevent wave parallelism between the speaker and opposite wall to avoid the production of standing waves.

The principal object of the invention, therefore, is to facilitate the obtaining of reverberated sound.

Another object of the invention is to provide an improved system for obtaining reverberated sound.

A further object of the invention is to provide an improved reverberation system of miniature size and low cost.

A better understanding of this invention may be had from the following detailed description when read in connection with the accompanying drawings, in which:

Fig. 1 is a perspective view of a reverberation chamber embodying the invention;

Fig. 2 is a cross-sectional view of the reverberation chamber shown in Fig. 1 and its outer enclosure taken on a plane corresponding to the line 2-2 of Fig. 1 and viewed in the direction of the appended arrows;

Fig. 3 is a cross-sectional view of the reverberation chamber shown in Fig. 2;

Fig. 4 is a cross-sectional view of the loudspeaker unit taken along the line 4-4 of Fig. 2;

Fig. 5 is a detailed view of the microphone and its mounting taken along the line 5-5 of Fig. 2; and

Fig. 6 is a detail drawing of the microphone mounting taken along the line 6-6 of Fig. 5.

Referring, now, to the drawings in which the same reference numerals indicate the same elements, a rectangular casing 5 may be constructed of different types of rigid material, one such material being .109" steel which may or may not be treated externally with a mastic 6 such as that used to underseal automobiles. The chambers may be of different sizes, one satisfactory size being 24" x 38" x 60 /2" which has a volume of 32 cubic feet. Because the chamber is built of steel, the boundary absorptivity is very low.

To avoid excessive panel vibration, the chamber is stiffened internally by 1" thick steel pipe braces. For instance, between the walls 8 and 9 are pipes 10, and between the

walls

12 and 13 are pipes 14, and between the upper wall 16 and bottom wall 17 are pipes 18. Although a certain number of stiiiening members are shown for the purpose of illustration, more or fewer stifiening members may be used if desired, depending upon the amount of stiffening required. Angle iron may also be used as stifiening braces.

In addition to preventing excessive panel vibration, the pipes also act as sound difiusers within the enclosure. Furthermore, at the lower left-hand corner of Fig. 2 is shown a panel deflector 20 at approximately 45 degrees to the adjoining walls, this deflector aiding in deflecting the sound between the walls 8 and 9 as mentioned above.

To introduce sound into the chamber 5, a loudspeaker shown generally at 21 is mounted in an opening in the wall 16 as shown in detail in Fig. 4. The loudspeaker may be of any general type, having a casing 23, a magnet 24, a voice coil 25, and a diaphragm 26. The casing 23 is fastened to the wall 16 by machine bolts 28 through a flange 30, the casing 23 and wall 16 being separated by a rubber gasket 29. The outer rim of the loudspeaker diaphragm 26 is mounted on a ring 31 on which a support 32 for the magnet 24 and conductors 33 is also mounted. The seal is such that a vacuum may be created within the chamber 5 to permit the high density gas to be subsequently introduced in the chamber.

Also attached to wall 16 is a microphone support which includes a collar 35 supporting three rods 36, at the lower ends of which is mounted a microphone 37 within a collar 38, to which are attached springs 39 having their other ends connected to the rods 36. The microphone may be of any standard type, its output circuit being connected over conductors 41 to external apparatus. The mounting of the microphone is also such that a vacuum may be created within the chamber 5, the mounting consisting of a rubber gasket 42 interposed between a sealing ring 43 and the wall 16 and being held in position by machine bolts 44. Thus, sound is introduced into the chamber 5 by the loudspeakers 21 and detected by the microphone 37.

As shown in Figs. 2 and 3, the chamber 5 is enclosed within a second chamber 46 to insure a low noise level within the steel chamber 5 and to prevent the sound waves within the inner chamber from being transmitted externally. The enclosing chamber 46 is made of plywood 47 and is lined with approximately /2" of an acoustic material 48, such as acoustic tile. The chamber casing 5 rests upon vibration isolators 50 and is held in position by wedge blocks 51. The chamber 5 is exhausted of air through an opening 53, after which a gas, such as a selected type of Freon, is introduced therein to provide a, the desired reverberation time. After the heavy gas is in-the chamber 5, the opening 53 is closed in any suitable manner, such as by a plug 54. The reverberation time of a chamber having the above-mentioned dimensions and filled with Freon gas is of the order of approximately four seconds, which is-the same as a chamber twenty-seven times larger in volume and filled with air.

Two preferred typesof Freon gas are known as Du Pont dichlorodifluoromethane (CCL F type 12 and Du Pont monochloropentafluoroethane (CClF CF type 115.

We claim:

1. A miniature sizereverberation chamber system'capable of providing the same reverberation times as those of larger reverberation chambers comprising a firstenclosure, a sound-absorbing material along the integral surface of the walls ofsaid'enclosure, a second enclosure Within said first enclosure in spaced relation to said sound absorbing material, a plurality of braces extending between-the opposite walls ofsaid second enclosure for preventing excessive vibration thereof, means enclosed by said first enclosure and disposed-in the space between said second enclosure and said sound absorbing material for projecting sound waves within said second enclosure, means Within said second enclosure for detecting sound waves within said second enclosure, and a gas Within said second'enclosure, said gas-having a density greater than air.

2. A miniature size reverberation-chamber system in accordance with claim 1 in which said means for-projecting sound waves within said second enclosure is carried by said second enclosure and extends therefrom outwardly into'said space.

3. A miniature size reverberation chamber system in accordance with claim 1 in which the density of said gas is approximately nine times that of air to provide a reverberation time comparable to an enclosureapproximately twenty-seven times as large in volume assaid second enclosure.

4. A miniature size reverberation chamber system-in accordance with claim 1 in which said gas is a type-of Freon.

S. A miniature size reverberation chamber system capable of providing the same reverberation times as those of larger reverberation chambers comprising a first enclosure a sound absorbing material along-the internal surface of the walls of said enclosure, a second enclosure within said first enclosure and-air spaced therefrom, a plurality of braces extending between the opposite walls of said second enclosure for preventing excessive vibration thereof, means enclosed by said first enclosure for projecting sound waves within said second enclosure, means within said second enclosure for detecting sound waves within said second enclosure, a gas within said enclosure having a density greater than air, and a sound wave deflecting baflle positioned within said second enclosure at approximately 45 to the wall opposite said means for projecting sound waves within said second enclosure.

6. A miniature size, reverberation chamber system capable of providing the same reverberation times as those of larger reverberation chambers comprising a first enclosure, a sound absorbing material along the internal surface of the walls of said enclosure, a second enclosure within saidfirst enclosure in spaced relation to said sound absorbing material, means enclosed by said first enclosure'and disposed in the space between said second enclosure and said sound absorbing material for projectingsound waves within said second enclosure, means within saidsecond enclosure for detecting sound waves within said second enclosure, and a gas within said second enclosure, said gas having a density greater than air.

"References Cited in thefile of this patent UNITED STATES PATENTS 2,06

OTHER 5R EF ERENCES Knudsen: Absorption ,of'Sound in Air, Oxygen, etc., Journal of Acoustical Society of America, October 1933, vol. V, pages 1124121.

Beranek: Acoustic Measurements, published by John Wiley & Sons, Inc., New York, 1949, page 866.

"Hansen: Simple Echo, Box, Radio-Electronics Magazine, July 1952 pagesSl, 52.