Normalized impact level

Professional Definition

Normalized impact level (denoted as $L'_n$) is the sound pressure level of impact sounds in a receiving room, corrected with respect to normalized acoustic absorption ($A_0$). The reference value is typically $10 m^2$.

The formula for this level takes into account the measured sound level and the logarithm of the ratio of the actual acoustic absorption of the room to the reference absorption. This parameter is more commonly used in laboratory studies and in some Western European countries, as opposed to the standard level used in Poland in field conditions ($L'_{nT}$).

Acoustics in Simple Words

Think of it as currency conversion. You have a price in dollars and a price in euros. To know which is more expensive, you need to convert both amounts into one currency, e.g., zlotys. In acoustics, the “currency” is the size and absorption of the space in which we listen to noise.

If you tap on the ceiling above a small tiled bathroom, the noise will be different than above a large carpeted living room. Normalized level is a mathematical conversion that tells us: “what would the noise level be if the receiving room always had an ideal $10 m^2$ of absorbing surface.” This allows building material manufacturers to compare their products (e.g. underlayment mats) objectively, irrespective of the laboratory in which the test was conducted.

Summary

The normalized impact level ($L'_n$) is a parameter used to assess the sound insulation from impact sounds, correcting the result for the acoustic absorption of the room. It is crucial when comparing the properties of materials and partitions under laboratory conditions.