GB2083096A - Improvements in or relating to noise suppression - Google Patents

Abstract

The invention relates to a method of suppressing the level of noise from a noise source, at least a portion of which noise arises from the utilisation of air by the noise source for ventilation and/or operation, comprising the use of an acoustic enclosure the walls 16, 18, 16', 18', 24 and 32, of which comprise at least two leaves having a cavity therebetween, providing a supply of air to the noise source contained within the enclosure and causing said air to pass between the leaves of the walls so as to partake of an indirect path through at least a portion of said cavity before emerging therefrom, adjacent the noise source. A second example (Figs. 6-10 not shown) is given of an enclosure which incorporates the method. <IMAGE>

Description

SPECIFICATION Improvements in or relating to noise suppression The invention is concerned with improvements in or relating to noise suppression.

It is well recognised that an unduly high level of noise emission from operating machinery of all kinds has a deleterious effect on persons in the vicin ity not only in the form of physical damage to ears but also by contributing to the build-up of stress and tension. It has therefore become accepted that one way of reducing the level of noise from machinery is to provide an enclosure to surround the source of the noise. Such enclosures are commonly provided with sound-deadening material on their wall surfaces, but in use of these enclosures, whether removable or permanently secured in position, meets with varying degrees of success.

The location of a noise source within an enclosure can, as a result of the reverberant noise thus created, exacerbate the noise problem, which effect is conveniently reduced or avoided by the provision of a sound-absorbent cladding on at least one internal wall surface ofthe enclosure. A double or multi-leaf wall structure with suitable cladding produces notably more successful results than are achieved with a single-leaf wall.

However, such enclosures are only highly effective when the noise source is totally enclosed. However, most mechanical noise sources also produce a not inconsiderable amount of heat during their operation and unless precautions are taken, this will build up within the enclosure to excessive temperature levels. As a remedy, ventilation is employed but this usually involves the presence of ventilation inlets and outlets and loss of efficiency in noise reduction due to the escape of noise through the necessary apertures in the enclosure walls.

This may be to some extent offset by the provision of silencer systems through which the ventilation air passes before it enters the enclosed chamber containing the noise sources. However, such arrangements add bulk and weight to the enclosure and therefore to the effective operational size of the machinery comprising the noise source.

The invention provides a method of suppressing the level of noise from a noise source, at least a portion of which noise arises from the utilisation of air by the noise source for ventilation andlor operation, comprising the use of an acoustic enclosure the walls of which comprise at least two leaves having a cavity therebetween, providing a supply of air to the noise source contained within the enclosure and causing said air to pass between the leaves of the walls so as to partake of an indirect path through at least a portion of said cavity before emerging therefrom, adjacent the noise source.

Advantageously, air leaving said noise source may be caused to pass between the leaves of the walls through another portion of the cavity in partaking of an indirect peth as it leaves the enclosure.

The invention also provides, in another aspect thereof, an acoustic ensloure for use in the abovementioned method and having walls comprising at least two leaves having a cavity therebetween, said cavity providing at least one indirect passage between the exterior of the enclosure and the interior thereof which houses the noise source.

Conveniently, an example of an enclosure according to the invention may be rectangular in plan, the cavity being formed by the leaves of two adjacent walls of the enclosure providing a first passage between the exterior and the interior of the enclosure and a separate cavity being formed by the leaves of the two remaining adjacent walls. The path provided by each cavity will therefore be rendered indirect by the presence of a right-angled bend therein.

In another example, a cavity may be formed which provides a path between the exterior and the interior of the enclosure which passes along the wall cavity on all four sides of the enclosure, a first cavity portion extending over only part of the height of the walls, a further cavity portion being formed within the remaining height of the walls to provide a second passage along the wall cavity on all four sides of the enclosure. The two passages are thus superimposed one upon the other, and each passage will have at least three right-angled bends therein providing three abrupt changes of direction for the air passing therethrough.

If required, more than two passages may be provided within the height of the enclosure walls, arranged in a columnar or stacked formation. In all examples, wall surfaces are preferably clad with sound-absorbent material.

In each of the examples of the invention to be described below, the noise source is a compressor which is provided with an enclosure according to the invention. The type of compressor is that which is conveniently used to provide clean, compressed air in hospitals for use for example in life-support systems, the air being admixed with other gases if required. However, the noise emitted from an compressor has hitherto been found to result in increased stress and tension levels in patients, even when they appear two be unconscious.Enclosures according to the invention are capable of reducing the noise of such a compressor to a barely audible hum, without unwieldly bulk undesirable in a hospital ward, by replacing the silencer systems sometimes associated with conventional attempts to reduce noise from the compressor by a circuitous path through the cavity passages between the multiple walls of the enclosure.

There will now be described two examples of an acoustic enclosure in accordance with the invention.

It will be understood that the description, which is to be read with reference to the drawings, is given by way of example only and not by way of limitation.

In the drawings: Figure 1 shows a diagrammatic side view of an acoustic enclosure typical of the prior art; Figure 2 is a horizontal view on line ll-ll of Figure 1; Figure 3 shovvs a horizontal sectional view through a first example of an enclosure according to the invention; Figures 4 and 5 are fragmentary cross-sections on an enlarged scale of a detail of the enclosure; Figure 6 is a vertical section through a second example of an enclosure; Figure 7 is a fragmentary cross-section on an enlarged scale of a detail of Figure 6; Figures 8 and 9 are diagrammatic cross-section views on lines VIII-VIII and IX-IX respectively of Figure 6; and Figure 10 is an isometric view of the enclosure of Figure 6.

Figure 1 shows a compressor 2 within an enclosure 4 according to the prior art. The enclosure walls 6 (Figure 2) form a double-leaved construction having a closed cavity 8. Air supplied to the condenser is pass through an air path silencer device 50 to reduce the noise level at the air intake to the system. Air leaving the compressor system passes through a second air-path silencer device 12. The resulting construction is bulky and unwieldy.

Figure 3 shows a first example of an enclosure according to and for use with the present invention.

A compressor 14 is shown within an enclosure having four external walls 16, 18, 16', 18'. An inlet 20 and an outlet 22 are provided for the ingress and exit of air required by the compressor system. Adjacent the inlet 20, the exterior wall 16 joins with an interior wall 24 which runs parallel with the wall 18. A passage 26 is thus formed which corresponds to the cavity 8 of the device of Figure 2. This cavity 26 has a right angled bend adjacent the junction of the walls 18 and 16' and continues in the direction of the arrows until the end of the wall 24 is reached, giving access to the interior ofthe enclosure at 28.

Air from the compressor leaves the interior at a gap 30 between the wall 24 and the end surface of a second interior wall 32 which runs parallel with the wall 16 and 18' to provide a passage 34 leading to the exit 22.

The exterior and interior walls of the enclosure may be constructed from panels of sound-insulating material or, as in the present example, may be provided by structural walls having sound-absorbent cladding on their surfaces. Figure 4 shows the walls 32 and 18' (or 24 and 18) each having a layer of sound absorbing material 36 bonded to one surface thereof, and Figure 5 shows the wall 32 comprising two layers of the material 36, one on each surface thereof, corresponding to the arrangement shown in Figure 3.

A second example of an acoustic enclosure is shown in Figures 6-10. A compressor 38 is the source of the noise to be suppressed and is contained within the interior of an enclosure having four exterior walls 40. An inlet 42 for air to the compressor is provided in an upper region of one wall 40. The inlet leads to a passage 44 comprising that portion of the cavity which lies between the upper region of the walls 40 and an upper region of an interior wall 46.

The path of airtravelling along this passage is shown by the arrows in Figure 8, entering the interior of the enclosure through a port 48.

Air from the compressor 38 leaves the interior of the enclosure through a port 50 formed in a lower region of the interior wall 46 leading to a passage 52 formed by the portion of the cavity lying between the lower regions of the walls 40 and 46. The path of the air through the passage 52 is shown by the arrows in Figure 9, and leads to an exit 54.

The passages 44 and 52 are separated by a partition comprising two over-lapping flanges 56,58 most clearly illustrated in Figure 7. Flange 56 projects from the outside surface of the interior wall 46 and extends all round the interior wall ofthe enclosure which is constructed separately from the exterior wall 40 and may be removed from within the wall 40 by lifting. The enclosure is thus assembled by lowering the interior wall 46 until the flange 56 rests upon the continuous flange 58 projecting from the inside surface ofthe exterior wall 40. A resilient sealing material, in the present example a rubber strip 60, is interposed between the confronting faces of the flanges 56 and 58. The enclosure is completed by the provision of a double-leaved lid 62. All walls and the lid are clad with sound-absorbent material 64.

Various modifications may be made within the scope of the invention.

Claims (14)

1. A method of suppressing the level of noise from a noise source, at least a portion of which noise arises from the utilisation of air by the noise source for ventilation andlor operation, comprising the use of an acoustic enclosure the walls of which comprise at least two leaves having a cavity therebetween, providing a supply of air to the noise source contained within the enclosure and causing said air to pass between the leaves of the walls so as to partake of an indirect path through at least a portion of said cavity before emerging therefrom, adjacent the noise source.

2. A method as claimed in claim 1, wherein air leaving said noise source is caused to pass between the leaves of the walls through another portion of the cavity in partaking of an indirect path as it leaves the noise source and passes to an outlet from the enclosure.

3. A method as claimed in either one of claims 1 and 2 wherein the indirect path provides at least one abrupt change of direction through an angle of or in the region of 90".

4. An acoustic enclosure for use in suppressing the level of noise from a source, at least a portion of which noise arises from the utilisation ofair by the noise source for ventilation and/or operation, comprising walls having atleasttwo leaves with a cavity therebetween said cavity providing at least one indirect passage for a supply of air to the noise source between the exteriorof the enclosure and the interior thereof which houses the noise source.

5. An enclosure as claimed in claim 4, wherein the cavity provides at least one indirect passage along which air travels as it leaves the noise source and passes to an outlet from the enclosure.

6. An enclosure as claimed in claim 5, wherein the enclosure is at least substantially rectangular in plan, a first cavity portion being formed by the leaves of two adjacent walls of the enclosure provid ing a first passage between the exterior and the interior of the enclosure and a second, separate, cavity portion being formed by the leaves of the two remaining adjacent walls.

7. An enclosure as claimed in claim 5, wherein the enclosure is at least substantially rectangular in plan and includes a cavity which provides a path between the exterior and the interior of the enclosure which passes along the wall cavity on all four sides of the enclosure, a first cavity portion extending over only part of the height of the walls, a second, separate, cavity portion being formed within the remaining height of the walls to provide a second passage along the wall cavity on all four sides of the enclosure, the two passages being superimposed one upon the other

8. An enclosure as claimed in claim 7 wherein three or more cavity portions may be provided within the height of the enclosure walls arranged in a columnar or stacked formation.

9. An enclosure as claimed in any one of claims 4 to 8, wherein at least one surface of each of the enclosure walls is clad with sound-absorbent material.

10. An enclosure as claimed in any one of claims 7 to 9, wherein each cavity portion is separated from the adjacent cavity portion by a horizontal partition formed by two overlapping flanges, a first flange extending from the inside surface of an exterior wall of the enclosure and in supportive contact with a second flange which extends from the outside surface of an interior wall of the enclosure.

Ii An enclosure as claimed in claim 10 wherein a layer of sealing material is interposed between the first and second flanges.

12. An enclosure as claimed in any one of claims 7 to 11 wherein there is provided closure means in theform of a double-leaved lid.

13. An enclosure for use in suppressing the level of noise from a noise source, constructed and arranged substantially hereinbefore described with reference to a) Figures 3 to 5 b) Figures 6to 10 of the drawings.

14. A method of suppressing the level of noise from a noise source, substantially as hereinbefore described with reference to a) Figures 3 - 5 b) Figures 6-10 of the drawings.