Professional Definition

The steady sound level is the sound level at a specific location, observed using a sound level meter with the A-weighting and S (Slow) time weighting, which during the observation exhibits variability not greater than 5 dB.

Thus, it is a sound with a relatively stable envelope. The criterion variability ≤ 5 dB with a Time Constant of “Slow” allows treating such a source as stable, facilitating easier reading of the representative value directly from the meter, without the need for prolonged integration of the signal.

Acoustics in Simple Words

Imagine a stream of water flowing from a faucet under constant pressure. The noise you hear is steady, monotonous, and hardly changes. This is steady sound. Another example could be the operation of a fan in a computer under constant load or the noise of air conditioning in an office. The noise meter’s needle may flutter slightly in such a situation, but it does not make sharp jumps.

Summary

Steady sound is noise with a stable level, whose fluctuations are negligible (below 5 dB) from the perspective of measurement methodology. It is the simplest case for analyzing and assessing the impact on the environment or workplace.