SOUND CONTROL ADVICE
Understanding A-C-Z noise frequency weightings
What are the different frequency weightings and why do you need to know?
Understanding the difference between A-C-Z noise frequency weightings is one of the most important things you need to know about when measuring sound. This is because picking the wrong sound level meter weighting on your sound level pressure meter could mean your results become irrelevant for the purpose and at worst invalid (not legally compliant).
You may have noticed that some sound meters allow you to choose the frequency weighting you want to measure noise at. The three most commonly used decibel weightings are ‘A’, ‘C’ and ‘Z’ as defined in the sound level meter standards IEC 61672:2013 (BS EN 61672-1:2013), but which one do you choose? We explain this is more detail below, but if you own one of our Pulsar Nova sound level meters which measures all of these frequencies simultaneously, you need not ever worry about picking the wrong weighting.
What are ‘A’, ‘C’ and ‘Z’ weightings
| Frequency (Hz) | 63 | 125 | 250 | 500 | 1k | 2k |
|---|---|---|---|---|---|---|
| A-weighting (dB) | –26.2 | –16.1 | –8.6 | –3.2 | 0 | 1.2 |
| C-weighting (dB) | –0.8 | –0.2 | 0 | 0 | 0 | -0.2 |
| Z-weighting (dB) | 0 | 0 | 0 | 0 | 0 | 0 |
Why do I need to know this?
The human ear is most sensitive to sound frequencies between 500 Hz and 6 kHz. When measuring sound pressure level variations, especially for potentially damaging noise levels for workplace noise, it is important that the sound level meter is able to give an accurate representation of what the human ear actually hears. Frequency weightings do this by giving more weight to different frequencies over others (i.e. emphasising some frequencies and de-emphasising others).
A-weighting for noise at work
When measuring the impact of noise at work on hearing the A-weighted noise measurements should be presented (commonly displayed as dB(A), (correctly written as LAeq)). Representative ‘A’ weighted average noise level readings should be taken for each task undertaken by an employee and then using software or the HSE’s calculator determine an individual’s exposure level.
C-weighted decibels for noise at work
People often forget the need to assess the risk from any impulsive noise (very sudden short-lived noises, bangs and crashes). The C-weighting is used for this to give us the peak sound pressure for the impulsive noise that the human ear is exposed to dB(C) (or LCPeak).
Most modern sound level meters and dosimeters will measure both the LAeq and the LCpeak simultaneously.
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