Sound level A

Professional Definition

A-weighted sound level – the acoustic pressure level corrected according to the A-frequency weighting characteristic.

It is a single-number value of the sound level, in which the individual spectral components have been weighted according to the A-weighting curve (defined in the IEC 61672 standard). This curve is characterized by significant attenuation of low frequencies, which approximates the sensitivity of the human ear to sounds of low and medium intensity (corresponding to the 40 phon isophonic curve). The result is expressed in A-decibels [dB(A)].

Acoustics in Simple Words

The human ear is not an ideal microphone – it is almost "deaf" to very low bass (e.g., the hum of a refrigerator), and very sensitive to mid and high sounds (like a baby's cry or a horn). The A-weighted sound level is the measurement result passed through a filter that acts like sunglasses for the microphone. It dims (attenuates) what a person would not hear anyway, and exposes what is audible to us. Thus, the result in dB(A) tells us not about the physical energy of the wave, but about how loudly we perceive a given noise.

Summary

The A-weighted sound level is the standard for assessing noise hazards in the workplace and in the environment. It allows for an objective assessment of the subjective perception of loudness, ignoring those sound components that are physiologically less significant to humans.