IL23244A - Sound-absorbent coverings - Google Patents

Description

. . •πιηπ |Π3 ΤΪΙΠΙ"Τ ·π PATENTS AND DESIGNS ORDINANCE SPECIFICATION I (we) grjLZBR FEERBS, SOCIDSB OIYHS, a Swiss company, of tiinterthur, Switzerland and Br. YIAB-SXAH CHB£J, a Chinese citizen, of i-iusetaraetrasse 12, Uintherth r, Switzerland, SRZCn PHILIPP, a ©enaan citizen, of Scheideggstraese 2/53, Winthertaur, Switzerland do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:- This invention relates to sound-absorbent coverings for the interior walls or ceilings of buildings. It is particularly, although not exclusively, applicable to coverings for the ceilings of weaving she s.

According to one aspect of the present invention an element for a sound-absorbent covering for an interior wall or ceiling of a building comprises a perforate member behind which is disposed mineral wool sheathed in sheet plastics, the sheath being spaced from the perforate member by a distance at least equal to the radius of the perforations in the member.

Mineral wool, for example glass or stone wool, is a material having very good sound-absorbing qualities and, therefore, ceilings and in some cases at least parts of the walls of rooms which are to be sound-proofed are sometimes provided with perforate members behind which mineral wool is positioned.

The perforate members will usually be boards, plates, sheets or the like of substantially rigid material. To prevent dust and small pieces of fibre from the mineral wool from dropping on to articles and machines in the room the mineral wool may be wrapped in air-permeable acoustic paper before being positioned behind the perforate member. The humidity is frequently very high in works where textiles are being processed for example in weaving sheds, and in chemical works and this humidity may penetrate the acoustic paper and lodge in the mineral wool.

The wrapping of the sound-absorbent material in paper is, therefore, unsuitable for such locations and, accordingly, the paper may be replaced by plastics sheet, for example polythene sheet.

It has now been surprisingly found by measurement that although the sound-absorption is very good for a perforate member and mineral wool without a sheath and is very good for mineral wool with a sheath but without a perforate member the sound-absorption is considerably lower, at least in the frequency range from about 1 kc/s upwards towards higher frequencies, if the sound-absorbent covering consists of mineral wool, a plastics sheath and a perforate member. However, it has been found that by spacing the plastics sheath from the perforate member by an amount at least equal to the radius of the perforations in the member the high sound-absorption values which have been obtained for a perforate member and mineral wool and for mineral wool with a sheath but no perforate member can be obtained, particularly in the frequency range of 1 to 6 kc/s, although measurements in the frequency range above 6 kc/s have not yet been carried out.

According to a second aspect of the present invention a building has an interior wall or ceiling covered by sound-absorbent means comprising a layer of mineral wool against the wall or ceiling, the layer being sheathed in sheet plastics, and a perforate member spaced from the sheath by a distance at least equal to the radius of the perforations in the member.

The space between the sheath and the perforate member can be filled by an open-pored foam material or by a honeycomb (as herein defined). By open-pored foam material is meant, for example, a foam plastic or foam rubber whose pores form small ducts through the layer of foam material and are, therefore, permeable to air. The term honey-comb as used herein is intended to mean a structure consisting of a plurality of parallel, contiguous, open-ended cells separated by thin walls and it is to be understood that the cells may be of any cross-section, e.g. rectangular or triangular as well as hexagonal.

Pelt-like substances may also be used for filling the space between the sheath and the perforate member provided that the humidity in the rooms it is required to insulate is not excessive.

The invention may be carried into practics in various ways but the invention will now be described in more detail and two embodiments of the invention will be described by way of example with reference to the accompanying drawings in which: Figure 1 is in diagrammatic form and represents a section through a sound-absorbent covering in accordance with the invention. This figure serves to explain the effect produced by a construction in accordance with the invention and for the purposes of simplicity no means are shown for ensuring the spacing of the plastics sheath enclosing the mineral wool from the perforate member; Figures 2 and 3 are sections similar to Figure 1 through two practical embodimen s of the invention; and Figure 4 is a graph showing sound-absorption plotted against the sound wave frequency for various constructions.

Like parts have been given like references in all the Figures and in each of Figures 1 to 3 there is a ceiling or wall 8 on which a sound-absorbent covering is fixed. The covering includes a perforate member 1 which consists of any of the conventional building materials, for example sheet-metal, plaster, fibre board, plastics or any simila material. Perforations 9 with diameters ranging up to a few millimetres are provided in the member 1 at regular or irregular intervals. Mineral wool to act as a sound-absorbent material 2 is positioned behind the perforate member 1 and in order to protect it against moisture it is wrapped in a sheath 3 of plastics sheet material. The thickness of the sheet is, for example, a few hundredths of a millimetre, while the thickness of the layer of mineral wool may be 10-50 mm. A distance at least equal to the radius of the perforations in the perforate member 1 is maintained between the sheath 3 and the perforate sheet 1.

Figure 1 shows this distance as an ordinary air gap 7. In Figure 2 the gap is filled by an open-pored foam material 5 and in Figure 3 it is filled by a honey-comb 6 which may also be of plastics. In Figures 1 and 2 the perforate member is in the form of a shallow tray "but in Figure 3 the perforate member is a flat sheet.

The intermediate layer of open-pored foam material 5 achieves an additional sound-attenuating effect by the fact that the sound waves penetrating into the wall covering branch in the foam material 5 into a number of ducts of small cross-section extending in various directions, so that the sound waves are distributed uniformly over the surface, the energy of the sound waves already being reduced somewhat in the ducts before they reach the sheath 3 and the mineral wool 2.

The perforate sheet 1, the intermediate layer 5 or 6 and the sheathed mineral wool 3 are preferably assembled into composite elements whose size - for example 0.5 to 1 square m&tfPe - and the shape of whose surface - for example rectangular or square -may vary as desired and are determined solely by considerations of manufacture and building technique. A number of packages of mineral wool 2 each wrapped in a sheath 3 may be disposed side by side in one perforate member 1.

It is believed that the improvement of the sound-absorbent effect of the wall covering provided with the space 7 between the perforate member 1 and the sheath 3 in accordance with the invention may be explained as follows. Small air pistons, which are symbolised in Figure 1 and denoted by reference 4-, are induced to oscillate in the perforations 9 hy the incoming sound waves. These air pistons 4 act as substantially point sound sources for the sound propagated into the perforate member 1. In a construction in which the sheath 3 bears directly on the perforations 9, the formation and oscillation of the small air pistons 4 would substantially be prevented. The sheath 3 is then induced to form local oscillations near the perforations, there being a relatively high reflection of incoming sound waves in the case of a point source , because of the reduced flexibility of the sheath.

The space 7 enables the air pistons 4 to form and oscillate freely, so that the waves radiating from the individual perforations 9 - see reference 10 in Figure 1 - can form a wave front. In this way the sound meets the sheath 3 as a wave front and induces relatively large parts of the surface to oscillate, instead of only locally limited parts.

The sheath can follow these oscillations produced by the wave fronts much more satisfactorily than point excitations. The reflection of the sound waves in the perforations 9 #ηέΙ at the sheath 3 is greatly reduced and thus the sound-absorbent effect of the entire covering is greatly increased.

The open-pored foam material 5 improves the sound absorption because the sound waves radiating from the perforations 9 are distributed over a number of small ducts therein. The sheath 3 situated behind the foam material can thus be induced to oscillate over relatively large areas instead of only at specific points.

The x-aja.s of the graph in Figure 4 is a logarithmic scale showing the frequency in cycles per second, while the _-axis shows the absorption coefficient a detected in a Kundt tube, a = 1 denoting 100 absorption. By way of example, a = 0.3 corresponds to 30$ and a — 0.5 corresponds to 50$ absorption of the sound waves meeting the covering.

The results of the measurements for a as shown in Figure 4 were obtained using a mineral wool layer about 15 mm thick. The curve a shows the a values for the mineral wool alone, while for curve b the mineral wool was surrounded with a 40^ thick sheath of polyethylene.

The measured values which were obtained using a perforate member in which the perforations constitute about 20$ of its area, together with the mineral wool without a sheath give a curve which is practically identical to the curve b. The measured values for the case of the mineral wool without the sheath but with a perforate member have therefore not been shown.

For the combination of a perforate member with mineral wool packed in a sheath the values exhibited great dispersion, and are approximately in the cross-hatched area denoted by reference _c. These dispersions may be explained by the fact that in a number of test series the contact of the sheath on the sheet varied so that air pistons similar to those shown in Figure 1 developed to varying degrees in the various measurements and thus influenced the absorption coefficients a.

Finally, curve d shows the effect of a covering which was constructed in accordance with the invention as in Figure 2. The distance "between the sheath 3 and the perforate member 1 is filled by an open-pored foam material layer 5 approximately 3 mm thick.

While the size of the individual perforations 9 in the member 1 has no appreciable influence on the a curves, the position of the maximum absorption coefficient a in the frequency range can be varied by varying the total proportion of the area occupied by the perforations 9 in the member 1.

Claims (1)

1. to bo Claimo defining the invention are as An element for a covering for an interior wall or ceiling of a building comprising a perforate member behind which is disposed mineral wool sheathed in sheet the sheath being spaced from the perforate member by a distance at least equal to the radius of the perforations in the A building having an interior wall or ceiling covered by means comprising a layer of mineral wool against the wall or the layer being sheathed in sheet and a perforate member spaced from the sheath by a distance at least equal to the radius of the perforations in the member0 An element as claimed in Claim 1 or a building as claimed in Claim 2 in which the space between the sheath and the perforate member is filled by an pored foam as claimed in Claim 1 or a building as claimed in Claim 2 in which the space between the sheath and the perforate member is occupied by a comb herein An element for a covering for an interior wall or ceiling of a building substantially as described herein with reference to Figure 2 or Figure 3 of the accompanying 26th of insufficientOCRQuality