Sound absorption

When a wave hits a surface, part of the energy is absorbed by the surface. Put
simply, one can say that all the materials have an absorption factor and are thereby absorbent.

The absorption factor for different materials denotes how much energy remains in
the material. The factor is rated in percent and is weighted from 0 to 1. The actual unit of absorption is Sabine (Sa). A Sabine is the equivalent to one square metre of 100% absorption.

Typical resonant base structures are perforated Gyptone plasterboards.

Both the boards and the resonant base structures have a resonance frequency and will absorb around this frequency. Typical membranes are normal plasterboard walls as well as tightly sealed surfaces.

The membrane's resonant frequency will primarily depend on the surface's weight
and to a certain degree surface tension.

Cavity absorbents are based on resonant base structures, which are surfaces with
holes or gaps with a cavity behind them. The cavity can either be empty or filled
with porous material. Perforated plasterboards like Gyptone BIG are typical cavity
absorbents.

The actual absorption properties depend on both the degree of perforation and the
size of the cavity or more precisely on the cavity's impedance.

All of the building parts/materials have a more or less absorbing effect and are
thereby a decisive factor in the room's total absorption. Some building parts/
materials provide an absorbing contribution to the low frequencies and to the
medium and high frequencies. Therefore in many cases it would be an advantage
to use an absorbing product which has broad absorption that is reasonably spread
throughout the frequency range from 125 - 4000 Hz.