What are A, C & Z Frequency Weightings?

On your sound level meter or noise meter, you will often see references to frequency weightings, but what does this mean?

Our ears are most sensitive to frequencies between 500Hz and 6kHz and are less sensitive to frequencies above and below these. For a sound level meter or noise dosimeter to measure and report noise levels that represent what we hear, frequency weightings are used. These are electronic filters within the instrument that adjust the way the instrument measures the noise.

The most used frequency weightings you will see on a modern sound level meter, or noise dosimeter are ‘A’, ‘C’ and ‘Z’. The Cirrus Optimus Sound Level Meters will measure all three frequency weightings at the same time, saving you the risk of measuring the wrong parameter.

This is the standard weighting of the audible frequencies and reflects the response of the human ear to noise.

The ‘A’ weighting filter covers the full frequency range from 20Hz to 20kHz, but the shape approximates the frequency sensitivity of the human ear.

Measurements made using A-weighting are usually shown with dB(A) to show that the information is ‘A’ weighted or, for example, as LAeq, LAFmax, LAE etc.

This is a standard weighting of the audible frequencies commonly used for the measurement of Peak Sound Pressure level.

Measurements made using the C-weighting are usually shown with dB(C) to show that the information is C-weighted or, for example, LCeq, LCPeak, LCE etc.

This is a flat frequency response between 10Hz and 20kHz ±1.5dB excluding microphone response.

Measurements made using Z-weighting are usually shown with dB(Z) to show the information is Z-weighted or, for example, LZeq, LZFmax, LZE etc.

All frequency weightings are defined in the standards to which a noise measurement instrument is designed. For example, the frequency weightings used on a sound level meter are defined in IEC 61672:2003 (BS EN 61672-1:2003).