Maximum sound level

Professional Definition

The maximum sound level (usually denoted as $L_{Amax}$) is the highest root mean square (RMS) value of the sound level recorded over a specified measurement time interval, using a specific frequency weighting (most often A) and a time constant (Fast or Slow).

In acoustic engineering, this parameter is crucial for evaluating single acoustic events (Single Event Level). It must be strictly distinguished from peak level ($L_{peak}$). $L_{max}$ is an exponentially averaged value over a very short time (e.g., 125 ms for the Fast constant), which corresponds to human ear perception, while $L_{peak}$ is the absolute maximum amplitude of the acoustic pressure wave without averaging.

Acoustics in Simple Terms

Imagine you are driving a car through the city for an hour. Your average speed may be only 40 km/h because you often stop at traffic lights and move in traffic jams. However, at one point, while overtaking another vehicle, you accelerated to 80 km/h for three seconds. The maximum sound level is precisely that 80 km/h recorded on your speedometer at that one specific moment.

Another analogy is a lake surface. The average water level is the equivalent level ($L_{eq}$). However, if you throw a heavy stone into the water, a wave will be created, the crest of which will rise significantly higher than the calm surface – that highest point of the wave, which lasts only for a moment, is equivalent to the maximum sound level. This parameter determines whether a passing ambulance with its siren will wake you up at night, even if there is perfect silence for the rest of the night.

Summary

The maximum sound level ($L_{Amax}$) is an indicator used to identify the loudest moments during a measurement, which is crucial in assessing the nuisance of impulsive and traffic noise. It is particularly significant in acoustic analyses for nighttime, where individual loud events have a decisive impact on waking residents from sleep.