Membrane absorbers, also known as panel absorbers and diaphragmatic absorbers, use the resonant qualities of a membrane to absorb sound over a narrow frequency range. Membrane absorbers are made of pressed wood fibres, soft panels, as well as rigid or semi-rigid materials such as plastic. The panel will likely vibrate and produce sound waves when it is mounted on a solid wall and separated by a narrow air space. Also, the fibres will bend and some friction will be lost, resulting in the absorption of the sound energy. It’s worth mentioning that the resonant system includes both the springiness of the air and the mass of the fibres, so absorption occurs exactly at the resonance frequency.
Membrane absorbers are frequently used to control particular resonant modes inside small rooms. To succeed, they must be placed on the appropriate surfaces at maximum modal pressure. It’s worth mentioning that porous absorption inside the space will dampen de resonance and broaden the bandwidth. This bandwidth is also known as the Q factor of the absorber and it’s effective even when the desired frequency is not achieved. It’s extremely important to take good care of membrane absorbers since small changes can change the overall performance. Also, membrane absorbers are frequently customized for specific tasks.
The sound absorption coefficient is around 15 to 20 per cent and has a significant effect when the components join together. Typical examples include large glass areas of many modern buildings since they ensure that the reverberation time does not increase excessively for bass tones. These glass areas help balance the room’s acoustics and the glass is absorbent because of the frequency range.
As a final note, it’s worth mentioning that membrane absorbers work exclusively for bass tones, so they tend to reflect high-frequency sounds. Also, glass windows can produce echo effects, while wooden floors can produce drum sounds.