US2219440A - Sound absorbing construction - Google Patents

Description

Oct. 29, 1940. Q R BURGESS 2,219,440

SOUND ABSORBING CONSTRUCTION Filed July 29, 1937 I v Kaye/s v Patented 2 9,

UNITED S ATES PATENT OFFICE 3,219,440 scum: snsonnmo consraucnou Charles I. Bur e Bokeelia,

. assignments, to Burgess Battery Com- Fla assignor, .by

n w. Chicag 111., a p ration of Delaware Application July 29, 193'], Serial No. 158,328

' This invention relates to improvements in acoustical correction constructions and embodies the use of metallic foil as a sound-absorbing ma- The object of the invention is to provide an efllcient sound-absorbing construction which is exceedingly light in weight, flreprooi, and duracally treated according to another form of myinvention;

Fig. 3 is a detailed sectional view taken at 3-4 of. Fig. 1;

Fig. 4 is a vertical sectional view of a railway car installation; and

Fig. 5 is a perspective view, partly in section, showing a sound-absorbing blanket.

The ability of certain materials to absorb a relatively large portion of sound waves incident upon their'surfaces is well known in the art. Other materials reflect a greater proportion of the waves. In order to reduce the sound level within a room reflection oi the waves should be prevented as far as ossible. This may be accomplished'by lining the walls and/or ceiling of the room with a sound-absorbing material. Heretofore various porous materials have been used for this purpose, such as balsam wool, hairfelt, mineral wool, or ceramic products. This lining is sometimes faced with a sound-permeable membrane such as a loosely woven textile fabric, wire cloth, or perforated sheet metal or other selfsustaining material. A construction in which the sound-absorbing material is provided with a facing of perforated sheet metal is shown in Norris Patent No. 1,726,500, dated August 27, 1929.

* fines of the enclosure formed by the tile, furring In this construction the metal does not absorb any appreciable part of the sound but is used to metallic foil arranged, usually, as a lining for the interior of the walls or the ceiling of the enclosure whose acoustical characteristics are to be correoted. This lining may be composed of foil crumpled and packed into a space provided'there for inany desired manner, or it may be a single sheet of foil su'fliciently crumpled to provide the desired thickness, or it may be made up from a a plurality of superposed sheets of crumpled foil (4 to 8 sheets thus superposed give excellent results) or alternating sheets of crumpled and uncrumpled foil. The latter construction may conveniently be pre-assembled into a blanket as hereinafter described. The blanket may be used with or without a facing. The foil should not be more than 0.0008 inch thick; a foil 0.0004 inch .to 0.0008 inch in thickness is preferable. Aluminum foil is readily available and may advantageously be used since this metal is light in weight and corrosion-resistant. Other i'oils, such as tin, lead or copper may be used. A blanket to 1" in thickness is suitable although greater thicknessesmay be used where the greatest degree of sound absorption is desired. The foil should not' be crumpled and packed too tightly. For example, when aluminum foil is used, the density of the. packed foil body should be about 3 or 4 ounces per cubic foot. Metallic foil, when arranged as described herein, is a very eflective sound-absorber, particularly of the shorter sound waves.

The ceiling 2 of the room shown in Fig. 1 is covered, in effect, by a substantially continuous lining of sound-absorbing material made up from a number of panels of crumpled foil 4 supported in edge to edge relation by tiles 6. As shown in detail in Fig. 3, the faces of'the tiles are periorated, as at 3, and carry flanges i0 whereby the tiles andpanels are supported from iurrlng strips i2 attached to the ceiling of the room, as more fully described in Weiss Patent No. 1,738,469, dated December 3, 1929, and Norris Patent No. 1,833,174, dated November 24, 1931. The crumpied foil is arranged in a layer in the tile and the unit may then be mounted on the furring strips. The crumpled foil readily adapts itself to the constrip and ceiling.

The sound-absorbing body or panel may be spaced from the perforated facing, if desired, by providing spacers it which rests upon the tile and support the foil. This arrangement permits a more uniorm reflection of light from the exposed suriace and thus improves the appearance. The panels of foil may be formed by packing the material in the tile, bringing the upper level to a point lower than the completely filled unit by the thickness of the spacer, removing the panel .to insert the spacers, and replacing the panel in the tile. The metallic toll is sufficiently rigid to supportitself without sag ing app a y it the span between spacers is not too great.

A pre-formed acoustical blanket i8 is shown in Fig. 5. Three or more sheets of uncrumpied I should be permeable to the sound waves while sheet 20 may be imperviousor sound reflecting. The uncrumpled sheets serve to hold the blanket in shape, permitting rolling of the assembled structure for shipping. Other materials, such as paper or cloth, may be substituted for the uncrumpled foil sheets. If foil is used, sheet 20 may be slightly heavier to provide added strength to the blanket. When installed this blanket may be furred from the wall by strips 24 (Fig. 2) and the blanket covered by a perforated membrane 26 spaced from the blanket by strips 28. In this construction resonating chambers are formed between ceiling 30, blanket l6, and strips. 24, the necks of the chambers being defined by grommets 22. The effect of these chambers is to increase the absorption of sounds in the lower frequency range.

A transverse section of a portion of a railway car, the housing for the engines of 2. Diesel powcred locomotive, for example, is shown in Fig. 4.

The outer wall 32 of the car is subject to heat or cold depending upon the outside temperature and is rigidly attached to the framework of the car so that it responds to the vibrations caused by the engines, unevenness of the rails, or the heating of the air against the exterior surfaces of the car. A complete sound-deadening construction is illustrated, a vibration-damping device 34 be- ---withirr the enclosure, preventing the transmission of sounds through the wall of the car, damping the vibrations in the walls, and is at I the same time, a very efficient heat insulator.

The above described sound-absorbing constructions are particularly useful for absorbing sounds whose frequencies are greater than about 1,000 -cycles per second. Noises from typewriters,

adding machines, and'the clatter of dishes or that caused by the moving mechanisms of a Diesel engine, for example, are in this range. The number and/or size of the perforations in the facing sheet to provide maximum efliciency of the sound-absorbing construction vary with the wave lengths of the sounds to be absorbed. These considerations are fully set out in the Norris patent above referred to.

When used herein, the term sound absorbing construction is to be distinguished from sound insulating construction in that the former is intended to reduce noise level within an enclosure by limiting reverberation due to sound reflection from the walls thereof and thus must be exposed directly to the sound waves, and the latter is used to prevent the transmission of sound through a wall comprising the construction. A sheet or body is sound permeable if a major portion of sound waves on one side thereof are transmitted to the other side either by means of induced vibrations in the sheet or by the movement of the sound waves through poresor openings in the sheet or body.

The specific installations herein shown and described are intended as illustrative only and in no way limiting the application of my basic discovery herein described.

I claim:

1. An acoustical correction construction comprising, in combination, a wall or ceiling surface has of an enclosure, a plurality of elongated furring strips arranged on said surface, a sound absorbing blanket covering at least a portion of said surface in spaced relation thereto and supported by said strips, said blanket comprising a plurality of spaced superposed sheets'of metallic foil having crumpled metallic foil therebetween and grommetted together at distributed points between said strips.

2. The construction of claim 1 and including a sound permeable facing member covering and contiguous to the exposed surface of said blanket.

CHARLES F. BURGESS.

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