Technical details

 

What is acoustics ?

The science of sound, its emission, propagation and reception.
By extension, it encompasses all of the techniques aimed at improving the sound dissemination quality in all rooms.

What is a sound ? An auditory sensation produced by a rapid variation in air pressure. An acoustic vibration which is propagated in the form of a mechanical wave. It is characterised by : The frequency (Hz) The sound level (dB) What is a frequency ?   The frequency, which is measured in Hertz (Hz), gives the number of vibrations per second. It enables a distinction to be drawn between bass sounds (below 200Hz), mid-range sounds (200 to 2,000Hz), and treble sounds (above 2,000Hz). The human ear is capable of hearing sounds on frequencies between 20 and 20,000 Hz.

In the construction sector, usually you work within a frequency range of 125 to 4,000 Hz.

What is a decibel ?

A unit for measuring the sound level. Levels audible to the human ear :

• 0 dB = hearing threshold. - 120 dB = pain threshold.

 

 

What is acoustic correction ?

Different from acoustic insulation, it deals with the control of the propagation of sound within a room in order to control the sound level and optimise listening qualities.
It offers various possibilities :

 

• Improving the listening qualities in a room.
• Lowering the sound level of a noisy room to make it bearable.

A wise choice of materials that takes into account their absorption coefficient, the room's surface area, and the reverberation time, provides very good acoustic correction.

What is control of the incident sound energy ? This energy consists of transmitted energy and reflected energy.   The quantity of energy reflected, and therefore the sound environment, depends on the material, shape and state of the surfaces of the walls. What does reverberation time mean (Tr) ?   The time that sound takes to decay by 60 dB after the sound source stops. It is measured in seconds.

For good intelligibility, the reverberation time depends on the volume of the room.

Recommended reverberation time :

Type of room Reverberation time (250 Hz - 4000 Hz) Office 0.4 - 0.7 s Conference room 0.6 - 0.9 s Cinema 0.6 - 0.9 s Classroom 0.5 - 0.8 s Theatre 0.9 - 1.3 s

Sound level Tr = Reverberation time in seconds

What is acoustic absorption ?

The incident sound energy on the walls is split into transmitted energy, reflected energy and absorbed energy.

 

Depending on the material of the room's walls, it is possible to influence the quantity of energy absorbed and therefore reflected. The suitability of a material is assessed using the Alpha Sabine coefficient (αw) per frequency, which equals the following ratio :

 

Without absorption, the reverberation time and the sound level increase in the room.