Materials for noise regulation are used partly to abate noise between rooms within a building, or between inside and outside areas, and partly as absorbers or reflectors within a single room.
Sound barriers normally consist of heavy materials that block the passage of sound waves. An effective example is turf roofs in the vicinity of airports. Sound barriers are normally part of the construction itself, such as a concrete wall between apartments, but layers such as heavy plasterboard can also be added. Sound barriers should be complemented by effective sound absorbers. Most porous insulation materials can be used. In floors, good sound barriers can be provided by loose filled sand. However, while these materials can provide acoustic insulation against the higher frequencies - such as conversation, one must also provide sound insulation against step sound and other noise transmitted through the structure. To achieve this sufficiently, construction often has to include a floating layer or partitions that are not physically in direct contact with each other.
Noise absorption within a room involves suppressing echoes, reve-beration and resonance, whilst reflection involves directing the sound waves to where they are wanted. Absorbers and reflectors are primarily a design issue; room volumetry and textures are central factors. Acoustic brick walls, for example, have perforated brick surfaces exposed towards the room. Acoustic ceiling panels and hanging sound baffles are also often used. Fairly simple solutions such as woodwool cement slabs fixed or suspended from classroom ceilings are often seen. Lightweight insulation is also often used in combination with perforated plasterboard or other perforated wall cladding.
Because of their porosity, small holes, etc., acoustic materials will often collect dust. Exposed ceilings of mineral wool have been registered as shedding fibres, leading to serious indoor climate problems.
In general, most acoustic materials will simultaneously have other functions in a building, e.g. as construction materials and thermal insulation. The discussions concerning these materials will therefore be somewhat decentralized in this book.
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