Normalized level difference

Professional Definition

Normalized level difference – a quantity determined by a formula in which the sound pressure level difference is adjusted by the ratio of the acoustic absorbency of the receiving room to the reference absorbency.

Mathematically, this is usually expressed with a formula that takes into account the reverberation time in the receiving room. The aim of normalization is to make the sound insulation result of the partition independent of the conditions in the room where the measurement is made (the so-called receiving room). This way, the result reflects the properties of the partition itself in relation to standardized conditions (usually for absorbency A0 = 10 m²).

Acoustics in Simple Words

Imagine you are testing the sound insulation of a door between two rooms. If the room where you are listening (the receiving room) is empty, with smooth walls and no furniture, the sound will bounce off the walls (creating reverberation), making it seem louder and that the door is weak. If you clutter that same room with sofas and carpets, the sound will be quickly absorbed, making it seem like the door insulates excellently. Normalized level difference is a mathematical adjustment that "removes" the influence of furniture and echoes from the equation. It allows for the assessment of the quality of the wall or door as if they were always tested under identical, standard conditions, regardless of whether the room is empty or full of plush toys.

Summary

Normalized level difference is essential for the objective assessment of sound insulation in field conditions. It allows for the comparison of measurement results with normative requirements, eliminating errors arising from different acoustics of the receiving interiors.