Reduction of impact level (ΔL)

Professional Definition

The reduction of impact sound level, improvement of sound insulation against impact sound (ΔL) – the difference between the normalized impact sound level of the ceiling without flooring and with flooring, calculated according to the formula specified in acoustic standards.

In engineering terms, this parameter is expressed in decibels (dB) and serves as a measure of the effectiveness of the floor structure (e.g., screed on acoustic foam or panels on underlay). The formula can be simplified as: ΔL = Ln,0 - Ln, where Ln,0 is the impact sound level of the bare ceiling, and Ln is the level after the flooring is applied. The higher the value of ΔL, the better the acoustic protection.

Acoustics in Simple Terms

Imagine you are hitting a concrete block with a metal hammer. The sound is sharp, loud, and carries very far – this is the “bare ceiling” situation. Now imagine placing a thick, sponge-like mat on the same concrete and hitting it with the same force. The mat acts as a damper – it absorbs the impact energy before it reaches the concrete. The reduction of impact sound level (ΔL) is a number that tells us how thick and effective your “sponge” flooring is. If this parameter is high, it is like swapping hard shoes for soft slippers – the energy of your steps stays in your apartment instead of traveling through the ceiling to the neighbor below.

Summary

The reduction of impact sound level (ΔL) is a key parameter when choosing flooring materials and acoustic underlays. It defines the gain in insulation that we achieve after finishing the ceiling, directly translating into the acoustic comfort of the users on the lower floor.