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)). emphasising some frequencies and de-emphasising others). Frequency weightings do this by giving more weight to different frequencies over others (i.e. 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. The human ear is most sensitive to sound frequencies between 500 Hz and 6 kHz. The sound level meter standard IEC 61672 specifies the performance and tolerances for the frequency weighting curves to be used.
Measurements made are displayed as dB(Z) or dBZ, or LZeq, LZFmax, LZE – where the Z shows the use of the Z-weighting.
Often used in octave band analysis and for determining environmental noise. Z-weighted is the flat frequency response of 8Hz to 20kHz (+/- 1.5dB), this is the actual noise that is made with no weighting at all for the human ear (Z for zero). Or for example as LCeq, LCPeak, LCE – where the C shows the C-weighting. Measurements are typically displayed as dB(C) or dBC. This is c-weighted peak is for measuring impulse noise and is referred to as CPeak. Peak Sound Pressure Measurements are made using the C- frequency weighting.
The C-weighted frequency looks more at the effect of low-frequency sounds on the human ear compared with the A-weighting and is essentially flat or linear between 31.5Hz and 8kHz, the two – 3dB or ‘half power’ points. Measurements are commonly displayed as dB(A) or dBA or as LAeq, LAFmax, LAE.Ĭ-weighting – (C-frequency-weighting). Any approved sound level meter meeting IEC 61672 is mandated to incorporate at least an A-weighting filter. The ‘A’ weighting adjusts the sound pressure level readings to reflect the sensitivity of the human ear and is therefore mandated all over the world for hearing damage risk measurements. The human ear is most sensitive to sound frequencies between 500 Hz and 6 kHz (especially around 4 kHz) whilst at lower and higher frequencies the human ear is not very sensitive. ‘A’ Weighted is the most commonly used and covers the full frequency range of 20Hz all the way up to high frequency 20 kHz. It is defined in various international standards such as the IEC 61672, as well as in various national standards such as ANSI S1.4. A sound level meter weighting that makes its readings conform to a notional human hearing response. What are ‘A’, ‘C’ and ‘Z’ weightingsĪ-weighting – (A-frequency-weighting). 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. You may have noticed that some sound meters allow you to choose the frequency weighting you want to measure noise at. 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). Understanding A-C-Z noise frequency weightings ad the differences between them is one of the most important things you need to know about when measuring sound. What are the different frequency weightings and why do you need to know?