GB2312086A

GB2312086A - Anechoic Chamber

Info

Publication number: GB2312086A
Application number: GB9707005A
Authority: GB
Inventors: Alan Trevor Fry; Ian Evans
Original assignee: Sound Attenuators Ltd
Current assignee: Sound Attenuators Ltd
Priority date: 1996-04-12
Filing date: 1997-04-07
Publication date: 1997-10-15
Anticipated expiration: 2017-04-07
Also published as: GB9707005D0; GB9607656D0; LU90050B1; GB2312086B

Abstract

An anechoic chamber comprises sound-absorptive elements such as wedges 4 arranged on inner surfaces 1, 2, 3 of the chamber. A substantially sound-transmissive protective shield in the form of a cage 5, spaced inwardly of the wedges 4, protects the wedges from contact by persons or objects moving in the chamber. The protective shield may be formed of perforated sheet metal, or of a mesh of welded plastics or metallic material, or of a stretched fabric material. The open area of the shield is preferably approximately 50%. The shield may cover the entire chamber, or may extend only over the lower part of each vertical wall of the chamber (figure 3), or may comprise a geodesic dome structure approximating to at least a portion of a sphere or ellipsoid (figure 4).

Description

ANECHOIC CHAMBER This invention relates to an anechoic chamber. In order to measure sound levels in industrial situations, chambers providing acoustically field free conditions, known as anechoic chambers are often used.

Anechoic chambers are usually constructed with soundabsorptive elements in the form of wedges of sound absorbing material such as foam or glass fibre arranged on the inner walls. In a cuboid chamber these elements may cover all six internal faces including the ceiling and floor, or more conveniently, rooms with anechoic walls and ceilings can be erected on existing floors which may comprise concrete or another acoustically reflective material. The latter chambers, which are sometimes referred to as "semi-anechoic rooms", are included in the term "anechoic chambers" used in this description.

In a conventional anechoic chamber the sound-absorptive elements such as glass fibre wedges are exposed or faced with a wire mesh covering for protection. However, even where such a protective covering is provided, the sound absorbing material is still vulnerable to damage by unintentional impacts which can easily occur in an industrial environment.

According to the present invention an anechoic chamber comprises sound-absorptive elements arranged on at least some inner surfaces of the chamber and a substantially sound transmissive protective shield extending over at least a portion of the inner surfaces and spaced inwardly of the sound-absorptive elements so as to protect the elements from contact by persons or objects moving in the chamber.

Preferably, the protective shield comprises a cage of metallic material, for example, a cage of perforated sheet metal. The open area of the metallic material may be approximately 50% with the apertures therein of any covenient shape. Alternatively the cage may comprise a mesh of welded plastics or metallic material or a stretched fabric material suitably framed for support.

In one embodiment of the invention, a protective shield extends over the lower part of each vertical wall of the chamber, for example, up to a height of approximately 2.4m.

In another embodiment, the protective shield comprises a geodesic structure approximating at least a portion of a sphere or ellipsoid.

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a vertical section through an anechoic chamber according to a first embodiment of the invention; Figure 2 is a vertical section through an anechoic chamber according to a second embodiment of the invention; Figure 3 is a vertical section through an anechoic chamber according to a third embodiment of the invention, and Figure 4 is a vertical section through an anechoic chamber according to a fourth embodiment of the invention.

Figure 1 shows an anechoic chamber having a floor 1, vertical walls 2 and a ceiling 3 all of which are lined with sound-absorbing wedges 4 of glass fibre, foam or other sound-absorbing material. A protective cage 5 is arranged at a distance of a few centimetres from the tips of the wedges over all six surfaces 1, 2, 3. The cage is made from sheet metal walls which are perforated with holes to give an open area of approximately 50%. . This cage 5 transmits sensibly all of the sound generated inside the cage to the wedges 4 where the sound is absorbed. The cage is thus acoustically transparent except possibly for very high frequency sound waves.

Figure 2 shows an alternative anechoic chamber having a concrete floor 11 which is not provided with sound absorptive elements. A cage 15 is arranged to protect wedges 14 on the remaining five surfaces, ie, walls 12, and ceiling 13.

A further alternative chamber is shown in Figure 3. Since most potentially damage-causing impacts are likely to occur at heights where persons operating in the chamber move about, it may be sufficient for a cage 25 to cover just the lower regions of vertical walls 22 of the chamber. Figure 3 shows a cage 25 having four vertical walls of metallic material reaching a height of 2400mm and open at the top.

It is preferable for sound wavefronts emanating from a source in the chamber to impinge upon the cage at a right angle, since the apparent open area of the cage is then at its maximum. Thus the ideal cage for a point source would be a sphere centred on the source. In practice the source will be distributed and the sphere should be somewhat distorted.

Accordingly, Figure 4 shows an anechoic chamber including a cage 35 comprising a regularly faceted structure which is intended to approximate a hemisphere. The cage 35 is supported on a concrete floor 31 in the same manner as the cages shown in Figures 2 and 3. When a sound source is located at a point 6 in the centre of the cage 35, the angle at which wavefronts emitted from the source impinge on the cage more closely approximates to 900.

The invention as described provides a mechanically strong yet sound transmissive structure which protects the soundabsorptive elements without significantly affecting their anechoic properties.

Whilst specific embodiments of the invention have been described above, it will be appreciated that modifications may be made thereto without departing from the scope of the invention. For example, the size and shape of the cages can be adapted for use in different anechoic chambers. The cages could be perforated with any arrangement of slots or holes and could comprise a welded mesh, or a wire mesh or fabric stretched over a frame.

Claims

1. An anechoic chamber comprising sound-absorptive elements arranged on at least some inner surfaces of the chamber and a substantially sound transmissive protective shield extending over at least a portion of the inner surfaces and spaced inwardly of the sound-absorptive elements so as to protect the elements from contact by persons or objects moving in the chamber.

2. An anechoic chamber according to claim 1, wherein the protective shield comprises a cage of metallic material.

3. An anechoic chamber according to claim 2, wherein the cage is formed from perforated sheet metal.

4. An anechoic chamber according to claim 2 or 3, wherein the open area of the metallic material is approximately 50%.

5. An anechoic chamber according to claim 2, wherein the cage comprises a metallic mesh.

6. An anechoic chamber according to any preceding claim, wherein the protective shield extends over the lower part only of each vertical wall of the chamber.

7. An anechoic chamber according to any one of claims 1 to 5, wherein the protective shield comprises a structure approximating at least a portion of a sphere or ellipsoid.

8. An anechoic chamber substantially as hereinbefore described with reference to any one of the accompanying drawings.