Castle Group Ltd

Octave band measurement is used when the frequency composition of a sound field is needed to be determined. Octave analysis is used in noise control, hearing protection and sometimes in environmental noise issues. Ten octave bands are commonly used for this purpose - 31Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz and 16kHz.

Although they are defined by the centre band frequency, the filter characteristics are quite broad and internationally standardised. An octave filter effectively attenuates frequencies which are greater than 1.414 and less than 0.707 of the centre frequency (e.g. the 2 kHz filter stretches from 1.41 kHz to 2.82 kHz).

Third Octave bands may also be measured by a suitable noise meter to give a more detailed analysis of a sound source.

Example of an Octave Band Analysis Graph

Noise Control - Octave band measurements are most often performed with an un-weighted filter network, i.e. Z (or Linear), so that the distribution of the energy source can be assessed. Although the work in the noise control field is often best left to the specialist, as noise control measures may involve treating multiple noise sources, each exhibits complex modes of vibration.

Octave band measurement should also be used when determining suitable hearing protectors prior to use as many hearing protectors have different level of protection at various frequencies.