Equivalent weighted index of the normalized impact level

Professional Definition

The equivalent weighted standardized impact sound level (denoted as L'n,w) is a single number representation determining the acoustic insulation of floors against impact sound, corrected for the acoustic absorption of the receiving room.

This value is determined based on field measurements using a standardized tapping machine. This parameter takes into account the reference curve adjusted to the sensitivity of the human ear (weighting) and correction for reverberation time in the room (normalization), which allows the result to be independent of the furniture in the room where the measurement is made. It is a fundamental indicator verified in Polish construction standards (PN-B-02151-3).

Acoustics in Simple Words

You can think of this indicator as an assessment of permeability of the ceiling for vibrations. Imagine that the ceiling is a sieve and your neighbor's footsteps are water being poured onto that sieve. L'n,w tells us how much of that water (noise) will leak into your apartment. The smaller the number, the denser the sieve, and less noise reaches below. A value of 50 dB indicates a good standard, while 65 dB may mean you'll hear every falling object from your neighbor.

Summary

This is the most important parameter determining how quiet it will be in the room below a ceiling where someone is walking. A low L'n,w indicator value indicates high-quality construction and the use of effective floating floors, which directly translates into the acoustic comfort of the residents.