US2060241A - Sound absorbing structure - Google Patents

Description

Nov. 10, 1936. T. M, PRUDDEN SOUND ABSORBING STRUCTURE Filed June 14, 1933 iw/z ,..IUWUHW wwwH/w...

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UNITED STATES BAT-ENT OFFICE SOUND ABSOBBING STRUCTURE Theodore M. Prudden, Hingham Center, Mass., assigner to Pacific Mills, Lawrence, Mass., a corporation of Massachusetts Application Juno 14, 1933, scrlol No. 675,766 1s claim, (ci. 154-44) This invention relates to a method of absorbing Fig. 2 is a view similar to Fig. 1 but illustrating sound and to an acoustic facing for the walls of a modified method of applying the facing panels. rooms and other enclosures absorbing sound ac- Fig. 3 is anvenlarged sectionl detail of a panel cording to my method. It operates, though in taken along line 3 3 of Fig.

5 somewhat varying degree, both in preventing Flgr-i isanenlarged sectional detail of a side v 5 sound enteringa room, leavingaI room, or causing edge of the panel also taken along line 33 of undesirable echoes and reverberations or otherre- Fig. 1. l f-th 1 f F1 3 suits in a room. Thus this method functions Fig. is a p an ew o e pane o 'g.

` both to absorb the sound and to insulate against My invention for convenience is constructed ina the transmission of sound through my material. the form of a panel for application to the wall I2 .10 In the claims the term sound absorbing covers or other surface that is to be acoustically treated. both these functions. The panels are conveniently rectangular and each There are many sound absorbing materials consists of a sound absorbing body section I4 and known which absorb sound and are explained in a cover or 'facing I6 that is applied to the inner prior patents. My method of sound absorption is, or front face of the body I4 and preferably has l5 I believe, new. It consists in placing in the path its side edges I8 reiiexed over the side edges of of the sound waves a. series of spaced, loosely the body H thereby Partl'yfto enClOSe the body hung, light, resilient sheets which are set in viand 9150 t0 form an Ornamental boundary fOr tration by the sound waves striking them (which the ranchy The cover plate I6 preferably 1s com: may or may not be individually vibratorily regggroglsgtlmrlmtggiga leffilf Cl'gllls, zo sponsive thereto to re roduce the sound) but a f S which in the aggregatepchange a, large part' of sheet should be chosen to reflect the desired per the sound waves to a form of vibration which is enttge. usually tiljie leeastuposslboangnf h not returned to the room or sed thro h the 501m Waves Tem ng e P01' n e ec e acoustic material as audiblepund. Tg apply 01 absorbed# Passing thrugh- A Sheet 0f hard this method of sound absorption by vibration I sisal felt isvfor most rooms satisfactory since itis have designed an acoustic panel which carries out ggg? gig 'ullpgigtgrs g 'f i l mrnglft oolsf lollgcrprfos some 28%, unchanged from its surface and takes pai'nt outside covering is desirable which will be attracedigm na'dfultion-othg cogr sheegi la. 30 tive in appearance, will permit of decoration and 'Si d :o anvid e lrwntha tsar mg Sec on will not interfere unduly with the acoustic results l aed Tgm a' s' 4 iae a a'nf e on?" of the remainder of the panel. Moreover, even men e sec lon s compose o an ou er with the best. known meth thin sheet 20- which may be a loosely mounted ods of treating the o n inner l light thin paper preferably of the tissue type,

c oth materials of my panel it is always but metal foil or other suitable readily vibrative desirable to add to the fire resistant qualities of material may be used very little s 01m d is M the whole panel. An outer coating of a fibrous ected fmmtms Sh..

ee It ordinarily vlbrates to mammal properly' reproofed will act like the the sound Waves reaching it and transmits themscreen around a miners safety lamp and apprewithin the sheet v Whatever the cause of its M iably delay the penetration ofthe names through 1 m Eh =t ti A i f 1 d tion, however, I find its use advantageous and its e o er "0a ngcoord ng Y Ihave Suggest@ omission harmful. In contact with the paper Such a facing, which, however, need not be used Sheehan two supomposed layers 22 and u of if the circmstances do not require ,1t *mi mm thin loosely woven cotton cloth resembling toit undesirat? e banco cloth. Next are two other superimposed The Partlcular Panel here Shown thmlgh efloyers of similar cloth 26 and 2s that are spaced f ective, may be varied to a substantial extent acfrom the mot mentioned cloth layers 22, 24 by cording to the requirements of the enclosurevin thr'eo Manel spacers 30, two disposed at the which it is to be used without departing from my oppgsite edges of the sections and the third disso method- Special details of construction. which posed inthe middle of the section. The spacers 6o are 0f advantagein VaI'OllS illll'llsl'fl'lesr are can `be of any suitable material as cloth, felt or hereinafter given more in detail in the Speoicaother material and canv be relatively thick as tion and referred to in the claims. l compared with the thickness of the cloth layers Fig-1 is a plan View of a portion oi' a wall hav'- 22, u2 4 and 26, 2 8. A thickness of 11o inch is quite ing' my improved facing panel thereon. satisfactory. 'I'he width can be anything necesshould preferably not be so wide as to overlie a large area of the cloth layers. The spacers are as long as the length of the section I4. Since it is convenient to make the sections about 16 inches square, the spacers will be 16 inches long. The section is further provided with two additional superimposed similar cloth layers 32, 34 separated from the layers 26, 28 by spacers 36 similar to the spacers 30 and a fourth strata of superimposed layers 38, 40 of similar cloth spaced from the layers 32, 34 by spacers 42. A single sheet 44 of Vcloth is superposed on the multiplicity of sheets 38 and 40 and is spaced therefrom by the spacers 46. A single sheet 46 ofl thln paper, tissue for instance, is interposed between a single layer 44 and the double layer 38 and 40, and is superimposed upon the layer 40 and is held in place by the middle spacer 46, the sheet having its side edges terminated close to but short of the outside spacers so that the paper sheet is confined only in its middle and the ends are free and unconiined, as is the paper sheet 2|). Next to the single sheet 44 is a second single sheet of cloth 50 which is spaced from the sheet 44 by spacers 52. Next is a backing sheet 54 which is spaced from the sheet 50 by spacers 56. The backing sheet preferably is a sound reflecting sheet for which purpose a kraft paper sheet is quite satisfactory. lA sheet of polished metal foil can be used as the backing sheet. A single sheet of thin tissue paper 58, crepe for instance, is interposed betweenv the sheets 50 and 54 and is superimposed upon the sheet 50 and is held in such position by the middle spacer 56, the ends of the crepe sheet being terminated close to but short of the end spacers 56 so that the sheet is bound into the section only at its middle. The various layers and spacers together with the cover plate I6 are all bound together in the aforesaid relation by suitable bindlng means as the binding wires 6D which pass through the superposed layers and spacers. The panels as thus constructed are secured to a wall i2 or other surface by suitable patches 62 of an adhesive that is applied to the wall and to the innermost sheet 54 of the panel or in any other suitable manner that does not interfere with the function of the panel, the panels being arranged with their edges in line as illustrated in Fig. 1, or staggered as in Fig. 2, or in any other suitable arrangement. All the layers of the section and particularly the interior layers are loosely draped between the spacers. Being so hung and being light and resilient they are individually (or in pairs when hung in pairs) vibratorily responsive that is, they flap, in response to the sound waves. I have found that on account of this loose hanging and vibratory responsiveness the sound Waves received are absorbed. This absorption may be in one or more of several Ways. The mere change of the sound waves to a vibratory motion not producing audible sound will itself, of course, destroy the sound wave so changed but also, if a sheet, for instance the first tissue sheet 20, actually vibrates so as to reproduce the sound it receives that wave proceeds to the next sheets and is ultimately damped out by them. The paper sheets are treated in any suitable manner to render them fire-resistant. One of the advantages of crepe paper over a tissue paper is that it can be obtained flreproofed. The fabric sheets and also the spacers are also rendered fireproof or fire-resistant. To this end they can be impregnated with a 25% solution of water glass and then after being dried can be treated with a 10% solution of a flreproofing solution known as Blackstone salts, which probably combines with the water glass and forms a compound that is not harmfully affected by varying humidity conditions. The water glass and also the iireprooiing salt treatment imparts a certain amount of stiffness to the cloth which facilitates its assembly into the panel.

A reflected sound wave from an inner part of the panel may be out of phase with a vibrating outer sheet, as for instance, the sheet 20, so that the reflected wave tends to reduce by interference the vibration of the sheet and the sheet to damp the reected wave. It is difficult to state to what extent this fact may affect the efficiency of the panel as a whole.

The words textile fabric are used in this speciflcation broadly to include felts and paper except where limited by the context.

I claim:

1. A sound absorbent panel construction cornprising a multiplicity of slightly spaced looselydraped light, thin individually vibratile sheets located between stiffer cover and backing sheets, at least the cover sheet being sound permeable, and means uniting all sheets into a unitary structure.

2. A sound absorbent structure comprising a multiplicity of superposed closely-spaced layers of loosely-draped light, thin, vibratile sheets, some of the layers consisting of a plurality of superimposed sheets and other layers consisting of a single sheet the spacing between the vibratile sheets being not materially greater than one-sixteenth of an inch.

3. A sound absorbing panel comprising a multiplicity of slightly-spaced loosely-draped light, thin, vibratile sheets, some being a textile material and some being paper, the paper sheets being in loose contact with confronting textile sheets.

4. A sound absorbing structure comprising a freely vibratile sheet, and a second sheet overlying and bearing lightly and loosely upon said vibratile sheet.

5. A sound absorbing structure including a freely vibratile sheet, a support for peripheral portions thereof, and a second sheet attached to said support and having a free unattached portion overlying and lightly engaging loosely a surface of said vibratile sheet, said two sheets being capable of relative movement therebetween in response to the sound.

6. A sound absorbing structure comprising s. series of confronting slightly-spaced light loosely draped sound absorbing sheets capable of vibrating under influence of the sound, the sheets having confronting free faces and the spacing between the sheets being not materially greater than one-sixteenth of an inch.

7. A sound absorbing structure as in claim 6 there also being sheets that are in loose contact with said first named sheets.

8. A sound absorbing structure as in claim 6, the sheets being in the main composed of material having the nature of tobacco cloth.

9. A sound absorbing structure as in claim 6, the sheets being thin and largely sound-permeable.

10. A sound absorbing structure compridng a series of confronting slightly-spaced light thin sound absorbing sheets capable of vibrating under influence of the sound, and empty spaces bctween the sheets,l the spacing of the sheets being only about sufficient to permit independent vibration of the sheets, a sound reflecting backing sheet confronting and disposed at the end of said series of sound absorbing sheets and means connecting all sheets into a unitary structure.

11. A sound absorbing structure as in claim 10,

some of said sound absorbing sheets characterized by being largely sound-permeable, and other sheets interposed between certain sound absorbing sheets characterized by being largely sound reiiecting.

12. A sound absorbing structure comprising a multiplicity of confronting, thin, spaced, looselydraped, sound-absorbing sheets having free confronting faces and capable of vibrating under iniluence of the sound, spacers interposed between said sheets at spaced intervals, a thick porous sound penetrable cover which overlies and screens said sheets, and means which secures said sheets and spacers and cover together.

13. A sound absorbing panel comprising a. multiplicity of confronting, slightly spaced, looselydraped, sound-absorbing sheets capable of vibrating under influence of the sound, and connected to each other at widely spaced intervals, the spaces between the sheets being empty and not greatly in excess of that permitting independent vibra-- tion of the sheets, and an outer cover of porous sound-permeable material which screens underlying sheets.

14. A sound absorbing structure as in claim 13, said cover having its marginal edge portions refiexed to overlie the edge portions of the underlying sheets.

15. A sound absorbing `panel comprising a plurality of superposed spaced loosely-draped, soundabsorbing textile sheets capable of vibrating under influence `of the sound, the spaces between said sheets being empty', a sound-reflecting backing sheet, a sound permeable cover sheet, and binding means connecting said sheets at intervals,

and paper sheets interposed between certain confronting textile sheets and engaged lightly with one of the confronting sheets.

16. A sound absorbent structure comprising' a plurality of closely-spaced, loosely-draped layers of cloth, a paper backing sheet on one face of the structure, the cloth layers comprising a single thickness of cloth adjacent said backing sheet and a double thickness of cloth adjacent the opposite face, there being a thin loosely-draped paper sheet interposed between two cloth sheets y are located between certain confronting sheets but do not bridge the spaces therebetween and which bear loosely upon one of the confronting sheets.

18. A sound absorbing-panel comprising a multiplicity of light thin loosely draped slightly separated sheets, the sheets'being separated by an amount that is not greatly in excess of that permitting independent vibration of the individual sheets, and other light thin sheets overlying and in light loose contact with some of said first named sheets and operative to damp the vibrations thereof THEODORE M. PRDDEN.

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