Acoustic absorption and comfort

Noise is omnipresent and represents a considerable nuisance in our daily lives. Acoustic performance must be respected in order to effectively deal with noise and guarantee acoustic comfort for building occupants. Discover the principles of sound absorption, one of the elements constituting acoustic comfort, with insulation.

DEFINITION OF SOUND ABSORPTION

Acoustic absorption or correction aims to:

• limit reverberation,
• reduce the level of the sound wave,
• improve speech intelligibility in a room.

Acoustic correction of the sound environment of a room involves an architectural design carefully examined upstream of the project as well as the use of absorbent materials which make it possible to control the sound energy reflected on the walls.

The indices used to measure the acoustic correction are:

• Weighted absorption coefficient: αw
• Equivalent absorption area of ​​a room (m2): A(f)
• Reverberation time (s): T

DEFINITION OF ABSORPTION COEFFICIENT

The sound absorption coefficient defines the ratio between absorbed noise and incoming noise. This varies by sound frequency.

The absorption coefficient (αw) is between 0 and 1:

• Absorption coefficient = 0 : the material does not absorb any noise, the noise is therefore completely reflected.
• Absorption coefficient = 1 : all noise is absorbed by the material. Thus, a material with an absorption coefficient αw=0.8 means that it absorbs 80% of incoming noise.

In other words, more the coefficient is close to 1, the more absorbent the material.

THE CONCEPTS OF SOUND ABSORPTION

What is acoustic comfort?

Acoustic comfort is the perfect restitution of the sound message (speech, music) to listeners regardless of their location in the room without degradation (echoes for example). A mix of absorbent and reflective surfaces is necessary for maximum acoustic comfort.

What is reverb?

Reverberation is the prolongation of a sound after the interruption of the sound source following multiple reflections on the walls of a room. The reverberation duration corresponds to the time necessary for a noise, after stopping the sound source, to decrease by 60 dB ⁽¹⁾ . It is expressed in seconds and defines the acoustic characteristics of the room. It is calculated in bands of thirds of octaves or octaves.

The reverberation duration depends on the frequency (see reminder below).

⁽¹⁾ Decibels (dB): The decibel is the unit of measurement for noise. It is equal to 10 times the logarithmic ratio between the measured intensity and the reference intensity.

 

REMINDER OF IMPORTANT DEFINITIONS TO UNDERSTAND SOUND ABSORPTION

Acoustic insulation makes it possible to limit or control the transmission of noise between different premises. The noises can be:

• aerial: speech, television, sound animations
• impacts: walking, shocks, vibrations
• equipment: ventilation, taps, air conditioning

Frequency quantifies the pitch of a sound. It is expressed in Hertz (Hz).

There are 3 types of frequency:

• bass frequencies (20 to 400 Hz)
• medium frequencies (from 400 to 1600 Hz)
• high frequencies (from 1600 to 20,000 Hz)

We only retain 6 frequency groups, each of them having a central frequency. These 6 groups, called octaves, are centered on 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz.