Weighted indicator of impact level reduction

Professional Definition

The difference between weighted impact sound levels of a normalized reference floor with and without a floor covering, obtained according to the method described in the PN-EN ISO 717-2 standard.

In the technical literature, it is often denoted by the symbol ΔLw (Delta Lw). It is a measure of improvement in sound insulation that a specific floor system contributes (e.g., a base layer on wool, carpet). This value is obtained by comparing the level of impact sound transmitted through the bare concrete ceiling and the same ceiling with a floor covering installed. The higher the ΔLw value, the better the protection against impact sounds.

Acoustics in Simple Words

Imagine hitting a hammer on a concrete table – the sound is sharp and loud. Now place a thick sponge on that table and hit it again. The sound will be significantly quieter and more muffled. Weighted reduction index of impact sound is a number that indicates how effective this “sponge” (i.e., a floor underlayment) is. Unlike many other acoustic indicators, here the more, the better, because we are measuring gain (noise reduction), not the noise itself.

Summary

This index (ΔLw) is fundamental when selecting floor materials, such as acoustic mats or carpets. It informs the investor how many decibels the floor will reduce footstep sounds compared to a bare ceiling.