There are a myriad of ways of measuring sound and noise. For this reason alone it is an area where even experts can differ on the finer points.
The following are some of the more common relating to noise disturbance.
L10: Denotes the level of sound exceeded for no more than 10% of the period being monitored.
This is a useful means of expressing noise from a frost fan as the cyclical nature of the sound varies considerably over a 5 minute period and averaging the noise conceals the peaks that are particularly disturbing.
Lmax: The single highest sampled level of sound. Used in night-time emission limits as a means of ensuring sleep protection. Short duration, high-level sounds such as audible warning devices, pressure relief valves have a significant effect on Lmax values.
L90: The level of sound exceeded for 90% of the monitoring period. This level of sound can be used to define the background sound level, and is influenced by constant sources such as industrial equipment and constant background city sounds, eg from air handling equipment. Noise emission limits are not generally specified in terms of an L90 level.
All the above units will typically be expressed using ‘dBA’ values. For instance 55dBA L10.
The readings that will be the most significant are those that are specified in the district plan as being the standard by which noise measurements are to be made.
This should always be your first port of call to ensure that you are comparing apples with apples for noise measurement.
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