Noise Terminology

Noise Glossary

Noise is notorious for its use of techno-babble in both the regulations and the data relating to it. The following definitions may help, (or may not...).

Noise survey vs noise assessment

These two terms are often used interchangeably with the intent being to mean the same thing however they do have different meanings.

A noise survey is technically a walk-though of a site with measurments of 'machine A is producing 86dB(A), machine B is 92dB(A), etc., often accompanied by a plan of the site. While this may give the employer some useful information, it is not sufficient to comply with the requirements of the noise regs.

A noise assessment on the other hand is an assessment of how much noise exposure people working there are receiving - it is based on personal exposures, not only on machine noise levels. A noise assessment must include an assessment of the risk and control or reduction measures.

The reasoning for this is that if you have a machine which is kicking out say 110dB(A) but nobody ever ever goes in the room where it is located when it is turned on, then the noise regulations to all intents don't really care about it - nobody is at risk. If on the other hand you have a machine which is kicking out 86dB(A) but someone works on it all day then the regulations are concerned about this.

To be clear, on our website we also switch between these two terms as we are trying to write clearly and in a way which people understand, but our noise assessment service is most definitely the latter, not a simple survey.


dB

dB stands for decibel - the unit of noise measurement. Not the most straight-forward of measurement units. If we have a noise at a set level, say 80dB and then double the amount of noise energy the measured value would increase by 3dB. Hence, 88dB is twice as dangerous as 85dB. To a human however a 3dB change is just about noticeable - it sounds like a small fractional increase in the volume. For a noise to sound twice as loud to a human we need to increase it by 10dB.

To try and put that in a simpler way... If we start with 80dB and double the energy we get 83dB but it only sounds a little louder. If we increase it to 90dB it sounds twice as loud. Confused yet?

TWA

The Noise Regulations say that employers have to identify people exposed to a maximum of 85dB(A) over an 8 hour reference period. This is basically an averaging system - someone with an hour in a loud environment followed by seven hours in a quiet one may overall have an 8hour exposure of below 85dB(A) and be exempt from the need to wear hearing protection. Don't be too reliant on this though - there is an upper limit of 87dB(A) which employees cannot be exposed to levels above so saying they can have 90dB(A) for one hour then the rest of the day of 80dB(A) to compensate is naughty.

Types

In relation to sound meters its basically an indication of accuracy. Type 2 is OK but has a degree of in-built variation (or put another way, has a wider range of error). Type 1 is the top one for noise risk assessments and has a much smaller range of variation and gives more reliable results.

Octave Band

Noise is made up of many many frequencies from deep bass notes to very high pitch whistles. We need to measure all these as the noise to which your employees may be exposed may be louder in different parts of the range. This is important with hearing protection as some are better with low frequencies, some with high pitches, etc.

'C' and 'A' Weighting

The ear doesn't hear 'normally', which sounds a tad daft but there you go. It hears different frequencies better than others and naturally enough is focused around the main speech areas, in effect hearing them more loudly than other less-important frequencies. When noise surveys are done an 'A Weighting' is used to make the noise meter mimic the way an ear hears, ensuring the result is closely aligned to the actual noise exposure received by a person. C Weighting is another correction system and is used in calculations for hearing protection suitability and for the peak level reached during a survey.

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