The input data useful for the implementation of an absorbing lining in an acoustic testing and measurement room are primarily:

  • the use of the room: normative requirements are associated with anechoic or semi-anechoic rooms which differs only in the properties of the ground (respectively absorbing or reflecting sounds); for users (in general: technicians and engineers or researchers in acoustics) needing a versatile facility (for their research and development - R&D - works), the convertibility of a room (with respect to anechoicity: full or half) can be obtained according to different principles and means, more or less sophisticated depending on the periodicity of the conversions and on the time allowed to switch from one configuration to another
  • the envisaged type of metrology: measuring the noise emitted by accelerating road vehicles requires a very specific environment (according to standard ISO 362-3, with a large number of aligned microphone sensors), other applications having - for most of them - in common to refer to standard ISO 3745, with a more limited number of sonometric lines - for sound pressure level assessment - and a measurement surface that is often parallelepiped or shaped semi-circular
  • the nature of the objects under test (size, sound spectrum): frequency band of interest, distances on the one hand between noise source and microphones and on the other hand between microphones and sound-absorbing lining are linked, the desire to have propagation conditions perfectly reproducing those of the free acoustic field involving testing means all the more voluminous and important as the tested object is large, and as the lower limit of the frequency domain of interest is low
  • the physical setting (area of available surfaces, acceptability of overweight for supports for the walls or for the roof and when applicable for the floor)

In very many cases, the reaction to fire of considered materials is also taken into account as well as considerations of appearance (even if the architectural bias is generally not as important as acoustic performance, colors and materials count when it comes to creating an atmosphere appropriate to prolonged work and worthy of a showcase for sometimes high-ranking visitors).

Specific constraints related to resistance to impacts or to weather damages may necessitate the use of particular absorbing linings (with waterproof, washable cover) or the use of stainless steels.

Other parameters may be involved such as the authorized mass, the required longevity or the available budget as well as (sometimes) thickness of the lining.

In the case of projects in the automotive industry sector, or for other industrial applications related to the transport or energy industries sector there is a utility, when it is not an absolute necessity, to have in semi-anechoic or semi-anechoic rooms, plane absorbers (e.g. apart from the advantage that this presents in terms of durability in hostile environments, to avoid the generation of noise linked to the airflow on surfaces with corrugations, such as in the case of conventional wedges). The walls of the experimental chamber, and sometimes other sections of the aeraulic circuit of aeroacoustic wind tunnels can advantageously be covered with a multilayer lining which combines dissipative materials (foams, wools) and a metal membrane to obtain an acoustic absorption coefficient of 100% over a frequency range as wide as is desirable for envisaged metrology.

Whatever the context, ITS masters the aspects of the question of useful data for choosing the sound-absorbing lining for an acoustic room (test-measurement).

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