Standard striking level

Professional Definition

Standard impact level (denoted as $L'_{nT}$) is the level of sound pressure from impact noises in a receiving room, adjusted for reverberation time. This adjustment refers to the standard reverberation time ($T_0$), which typically is 0.5 seconds for apartments.

This parameter is crucial in Polish building law (Technical Conditions) because it allows for the evaluation of the ceiling's sound insulation in conditions close to the actual use of a residential unit, detaching the measurement result from the current acoustic absorption of the room (e.g., the amount of furniture or carpets).

Acoustics in Simple Words

Imagine weighing a suitcase before a flight. The scale shows 20 kg, but you know it's on a slanted floor that always adds 2 kg to the result. To find the truth, you need to subtract this error. It’s the same with measuring impact noise (thumping).

If we measure noise in an empty, echoey room, it will seem louder than in a furnished room full of sofas and curtains that absorb sound. Standard impact level is the result of a mathematical operation that "zeros" out the influence of echo in your room. We bring the result down to a common denominator (the standard), as if every examined room had identical reverberation conditions. This way we know whether the ceiling is weak or if the room is just acoustically "empty".

Summary

The standard impact level ($L'_{nT}$) is a basic parameter for assessing the sound insulation of ceilings in Polish residential buildings. By referring to a fixed reverberation time (0.5 s), it allows for a fair verification of compliance with standards, regardless of the interior decor at the time of measurement.