Frequency Weighting Networks

A sound level meter must be designed so that it measures the sound level in the same way as humans hear. Weighting networks are frequency discriminating filters with special spectral shape that simulate the human hearing ability at different sound levels. Three networks are standardised in the sound level meter standard IEC 61672-1 and they are called A, C and Z.

The differences in A/C/Z

The A weighting filter is the most used network. All sound level meters must have this. It is used for finding the energy level of almost all kinds of environmental measurements. The C weighting network is often used to find maximum or peak levels in order to assess the risk for hearing impairment. The Z-network is flat and does not disciminate any normally audible sounds.

The difference between the A-weighted and the C-weighted levels provides information about the spectral properties of the sound measured and can as an example be used to find a suitable hearing protector for the actual noise environment.

All weighting networks shows the same level at 1000 Hz.

Some sound level meters (like this one) are able to show the octave or fractional octave filters overlayed the A-weighting curve. This is a practical feature because it shows clearly which frequency in the spectrum that contributes to the A-weighted level.