US2177393A - Sound absorbing structure - Google Patents

Description

Oct. 24, 193.9. 1 s. PARKlNsON 2,177,393

SOUND ABsoRBING STRUCTURE Filed June 8, 1937 QWW/4 Fig'. 4

INVENTo. JOHN S. PARK l NSON.

A ToRNEY.

A. o ,U O

. o: nl@ O mfc Q O n structures or treatments.

. UNITED STATES PATENTV IoEi-icE SOUND BSORBING STRUCTURE John S. Parkinsonlfsomerville, N. J., assignor to J ohne-Manville Corporation, New York, N. Y.,

a corporation of New York Application June 8, 1937, Serial No. 147,045

1s claims.

This invention relates to sound-absorbing relates to that type of sound-absorbing structure usually employed for the interior of rooms or Vauditoriums to eliminate objectionable reverberations and reduce the intensity of sounds, or reduce the intensity of sounds of certain frequencies occurring concurrently with sounds of vother frequencies which arenot to be reduced or eliminated. i

It is en object of this invention to provide a' sound-absorbing structure or treatment which can be employed to absorb sounds of definite frequencies and of definite frequency ranges. It is a further object of this invention to provldesuch -a a structure or treatment which can be employed to selectively absorb sounds of relatively high frequency as well as of relatively low frequency.

Other objects and advantages of this invention, if not specifically pointed out, will be apparent to those skilled in the art from the following detailed descriptions of what are now considered to be the'preferred embodiments of the present invention.

In the drawing:

Fig. l is a horizontal sectional view of a wall embodying the sound-absorbing structure. of the present invention;

Fig. `2 is a horizontal sectional view of a wally embodying a modified formy of sound-absorbing structure;

Figs. 3 and 4 are horizontal vertical sectionsoi walls embodying modified forms of the invention, and

Fig. 5 is a fragmentary elevational view of the Vwall shown in Fig.- 2.

Sound-absorbing structures or treatments heretofore known have not been effective over a major portion of theaudibility range, but have been limited in ei'ectiveness to either the low frequency range or the high frequency range of theentire audibility range.

Throughout this description, sound frequencies up to 500 cycles per second yare considered as being in the low frequency range and'sounds f -above 500 cycles per second are considered as being 1n the high frequency range. The total range over which sound treatment is desirable is usually between"50fand 8000 cyclesper second.

It will be appreciated that the aforementioned treatments do not become ineffective as sound absorbers at aJ definite frequency but gradually become ineffective over a considerable frequency range. Forexample, the sound-absorbing treatments which are considered effective over the low More particularly, it

frequency range diminish in effectiveness between 400 and V500 cycles, and those which are effective over the high frequency range diminish in effectiveness between 500 and 400 cycles, so that over a range of approximately cycles. 5 between 400 and 500, both treatments are effective but not to the'same extent as near the mean portion of their effective frequency range.

'I'he energy in sounds usually encountered in rooms or auditoriums is distributed over a wide 10 range of frequencies and it has not been possible heretofore to construct a sound-absorbing treatment which would adequately absorb all the component frequencies of the sounds to the desired extent because of the limited range over which 'a lli sound treatment could be made effective.

The present invention overcomes the deficiencies in existing sound-absorbing treatments o r structures by utilizing a diaphragm for the absorption of sounds in the lower-frequencies, and 20 providing a light, porous facing for the diaphragm, which4 may be formed of mineral wool, animall fibres, vegetable fibres, or similar materials, to absorb the sounds of higher frequencies. The light, porous facing absorbs the sounds in 251 the higher frequency brackets and at the same time does not impede the transmission of low frequency sounds to the diaphragm which, in turn, absorbs these low frequency sounds.

The diaphragm must be sufficiently impervious 3.0

other fibres, linen cloth impregnated with a suit-A 35 able ller, or thin metallic sheets. i

The sound-absorbing qualities of the' dial phragm may be varied by placing fibrous or other porous 'material behind. the diaphragm and suiiiciently in contact therewith to produce a damp- 40 .ing effect on the. diaphragm, and, in cooperation with' the diaphragm, to absorb low frequency sounds which would not otherwise be absorbed by the fibrous or other porous material alone. Referringlto Fig. 1, a wall 2 providing a base 4 member is shown in horizontal cross section. The wall 2 may be formed of any conventional material which is relatively impervious to air. It will be understood that by wall" all enclosures of a. room,including the ceiling, are to be in;- 50 eluded.

Furring members 4, which may be strips of wood or metal, are suitably attached to the face of thewallv 2 at spaced intervals. The face of the wall 2 is .usually substantially planar, and the spacing between Iurring members 4 may be varied as desired to adequately support the diaphragm and other elements of the sound-absorbing structure.

A diaphragm B, formed of the aforementioned materials, is disposed over and suitably connected to the furring members 4. The diaphragm 6 may be tacked or adhered to the furring members 4 by any suitable adhesive, and may be stretched tightly over the members 4 or permitted to re main relatively unstretched between the members 4 'if desired. The degree of tautness of the diaphragm is immaterial for the purposes of the present invention.

Porous sound-absorbing material 8 is disposed over the face of the diaphragm 6. This porous material may be a fibrous blanket formed of material such as hair felt or mineral wool, loose fibres, flaky substances, or other porous material, andrnay be adhered directlyto the diaphragm 6 by any suitable adhesive, fastened to the diaphragm by stitching, or otherwise held'in contact with the diaphragm. The porous material may also `be disposed over the face of the diaphragm at a distance therefrom and supported in any convenient way, if such is desired. The difference in the mass of the diaphragm when the porous material is spaced therefrom and when the porous material is carried thereby, and the absence of the damping effect of the .porous material on the diaphragm when the two are spaced apart, can be taken care of in the design of the structure, this requiring, however, a more cumbersome and expensive construction.

A decorative facing II'I which may be formed of any perforated or porous material may b e placed over the porous material 8 for the purpose of providing an attractive finished surface, but this finishing material I0 may be omitted if desired.

`The finishing material I0 may be supported in placel in any suitable way.

The structure shown in Fig. 2 is the same as that shown in Fig. 1 with the exception of the vibration-damping and absorbing material I2 which is placed behind thediaphragm 6 for the purpose of modifying the sound-absorbing characteristics of the diaphragm 6 in the manner previously explained.

The frequencies whichthe diaphragm will absorb are determined by the resonant frequencies of the diaphragm which, inturn, are controlled by the distance Whichthe diaphragm is spaced from the face of the wall 2 or other reflecting surface. The resonant frequency of the diaphragm may be Varied by varying this spacing and hence` the frequency at which the diaphragm is enabled to absorb sounds to the maximum extent may be varied.

It has been found that the frequency range over .which the diaphragm will effectively `respond can be materially broadened by causing the spacing between the diaphragm and the reecting surface, such as the face of wall 2, to continuously vary between definite limits. The limits may be f1 zero and any desired spacing distance, for example, 4 inches, or two different distances, for example, 1 and 4 inches. It will be understood that these limits are determined by the particular frequency ranges over which the material is to be effective, and the limits may be much greater or much less than those given to accommodate the particular installation desired.

A diaphragm which is disposed obliquely to a sound-reflecting surface, or at an acute angle to thejifsurface, effectively absorbs low frequency sounds over a very wide range and has a tendency to reflect sounds in the higher frequency brackets. In order to absorb higher frequency sounds, a facing of light, porous material may be disposed over the obliquely positioned diaphragm, as illustrated in either Figs. 4 or 5, in the same manne! as that described above relative to the diaphragm 6. Also, fibrous or other porous material may be placed behind the inclined diaphragm to act as a damping medium and, in combination with the diaphragm, as an absorber of low frequency sounds. A structure so formed is capable of absorbing sounds which include components in the low and high frequency ranges over a wide frequency range of each.

Referring to Fig. 3, the diaphragm I4 is positioned at an acute angle to the sound-reflecting surface of the wall 2 by passing it over some oi' the furring members 4 and under others of the furring members 4.

If it is desired to space the diaphragm I4 at a continuously varying distance from the reflecting face of the wall 2 without having the diaphragm I4 come in contact with the wall 2 and so as to make the lower limit of the space variation a deiinite distance instead of zero, the diaphragm I4 may be passed over two or more connected furring strips 4 at one point and between connected furring strips 4 at an adjacent point, as shown in Fig. 4. Instead of connecting furring strips 4 as shown in Fig. 4, thicker furring strips may be used at one point than at an adjacent point if such is desired. Also, the diaphragm I4 in the modification shown in Fig. 3 may be positioned relative to the furring strips 4 so as to be uniformly spaced from the surface of Wall 2 at some portions and at an angle to the wall surface at other portions. That is, the diaphragm I4 may be passed over two or more successive furring members 4 and then passed under or between the next connected pair of furring members 4. The diaphragm may be positioned parallel to the surface of wall 2 over some areas and oblique to vthe wall surface over other areas, and thereby produce a wide variation in the characteristics of the sound absorbing treatment.

High frequency sound-absorbing material l and vbe embodied in many different physical forms and is to be limited only by the appended claims.

What I claim is:

1. A sound-absorbing structure comprising a base member, a substantially air-impervious vibratile diaphragm spaced from said base member` and a layer of fibrous material disposed over the face of said diaphragm remote from said base member.

2. A sound-absorbing structure comprising a base member, a substantially air-lmpervious vibratile sheet of material capable ofabsorbing low frequency vibrations within the audibility range spaced from said base member, and a layer of material capable of absorbing relatively high frequency vibrations disposed over the face of said first-named material remote from said base member.

3. A sound-absorbing structure comprising a the diaphragm and base member.

5. A sound-absorbing structure comprising a base member, a substantially air-impervious visaid base member.

6. A sound-absorbing structure comprising a a substantially air-impervious viremote from said 10. A sound-absorbing structure comprising a air-impervious vimember, and porous sound-absorbing material l:disposed between said diaphragm and base mem- 11. A sound-absorbing structure comprisingy a air-impervious vibratile diaphragm disposed obliquely to said base porous sound-absorbing material disand a substantially air-impervious posed between said base member and diaphragm, and porous sound-absorbing material disposed over the face of said diaphragm remote from said base member.

12. A wall structure comprising a base member having a substantially plane face, furring members connected at intervals to the plane face of said base member, a. substantially air-impervious vibratile diaphragm disposed over the furring members, and porous sound-absorbing materia] disposed over the face of the diaphragm.

13. A wall structure comprising a base member having a substantially plane face, furring members connected at intervals to the plane face of said base member, and a substantially airimpervious vibratile diaphragm connected to said furring members so that intervening parts thereof are disposed at acute angles to the plane face of the base member.

14. A. wall structure comprising a base member, a substantially air-impervious vibratile diacovering disposed over the porous material.

15. A sound-absorbing structure comprising substantially air-impervious mote from said quency vibrations the face of said :first-named material remote from said base member.

JOI-IN S. PARKINSON.

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