![]() The letters A and C indicate which frequency weighting filter should be applied to the measured sound. Sound pressure and power and vibration amplitudes are commonly expressed in the decibel scale instead of the linear scale. The A-weighting system is designed to weight noise measurements according to this sensitivity gradient, which means that a very low-frequency noise that measures 50 dB in volume will measure significantly less in dBA. For example, maximum noise levels at work, as recommended by the World Health Organization (WHO), are L Aeq = 85 dB and L Cpeak = 135 dB. ![]() ![]() The Z-Weighting (no weighting and thus no filter) may be applied, for example, where an analysis of the sound source is required rather than the effect the sound has on humans, such as in testing the frequency response of produced loudspeakers in a manufacturing process.įrequency weightings are used when describing sound levels. The C-weighting filter is often applied when representing peak levels. Expert resources and advice to help professionals and businesses improve safety and health in the workplace check out the support we offer. It has everything you need to self-assess, learn and record your continuing professional development (CPD) Blueprint login. The A and C weightings are thus most meaningful for describing the frequency response of the human ear toward real world sounds.Īs acoustic sound level measurements are often motivated by the effect of sounds on humans, the A-weighting filter is commonly applied. Technically, the units that capture the human perception of a broad range of sounds are A-weighted decibels (dBA). Blueprint is an all-in-one package available to members. The C-Weighting curve represents what humans hear when the sound is turned up we become more sensitive to the lower frequencies. Acoustic sound contains more lower and higher frequencies than humans perceive. What humans are physically capable of hearing is represented by the A-Weighting curve. If a sound is produced with equal sound pressure across the whole frequency spectrum, it could be represented in the graph below by the Z-Weighting line. F. Certified sound level meters offer noise measurements with A, C and Z frequency weighting. Decibels with the sound pressure scale adjusted to conform with the frequency response of the human ear. The so-called A-weighted dB (abbreviated ) is based on the Fletcher-Munson equal-loudness curve for an of 40 phons. The scale used is called a weighted decibel scale or dB(A).
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