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Noise - Occupational - Control Intro

Increasing residential sound insulation is considered elsewhere. This section is of relevance internationally and mainly deals with control of industrial noise  [see Directory for suppliers of all hardware detailed below].

Before considering the subject in detail, there are some important points to consider.

  • Due to the logarithmic nature of noise levels , if a noise level is produced by say 10 equally loud noise sources, and five of them are totally "silenced", then the overall noise level will only fall by 3 dBA. If the reason for carrying out noise control is the protection of employee's hearing, then effectively you are doubling the period of exposure before damage occurs, and this would probably a worthwhile reduction. However, if environmental noise is the main concern, then resident's are unlikely to notice any improvement, and the reduction would only be worthwhile if it ensured that a noise limit was met, or a part of a package of measures.
  • Again due to the nature of the noise level scale, treatment to noise sources other than the loudest source, will make little, if any, difference to the overall noise level; for example if one noise source produces a level of say 90 dBA, and another 82 dBA, the overall level will be 91 dBA; therefore if an enclosure will reduce either of them by 10 dBA, it makes sense to use it on the louder one, because 90 + 72 (82-1) = 90 dBA, whereas 80 (90-10) + 82 = 84 dBA.
  • If a quotation or report states that noise levels will be halved, establish whether the sound energy or subjective response is being referred to. In sound energy terms "halving" is a 3 dBA reduction; in subjective response terms "halving" is around a 10 dBA reduction.

Many forms of engineered solution are frequency dependent, as are the performance of ear muffs and plugs. Thus frequency analysis is often used, both to identify noise sources and for the selection of control measures. There is some guidance on the selection of suitable Instrumentation here.

Selection of appropriate noise control measures depends on identifying critical noise sources and pathways. Without this understanding, control measures are often ineffective. For example it is no good spending money on "silencing" the quieter noise sources just because it is relatively cheap and easy. 

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