The performance of an acoustic test room (anechoic or semi-anechoic rooms, including: aero-acoustic wind tunnels), in terms of cut-off frequency (frequency above which the absorption coefficient at normal incidence of the absorbing element of the partitions is greater than 99% for walls, roof and where applicable - for anechoic rooms- floorl) is characterized by a measurement of a lining sample in a plane waves impedance tube. By extension (in fact: so shortened), the cutoff frequency is often referring to (in practice) the frequency above which the conditions inside the test room are those of a free (acoustic) field (in the case of a semi anechoic room: with a reflective floor), and sometimes: taking into account the tolerances set by the standard NF EN ISO 3745.

As an order of magnitude, a cutoff frequency below 50 Hz can be achieved with an absorbing lining with a careful design and with a careful implementation.

The performance of an acoustic test room (anechoic or semi-anechoic rooms, including: aero-acoustic wind tunnels), in terms of quality of the free field is very frequency dependent and is primarily related to the performance of the absorbing lining (for walls, roof and where appropriate - for anechoic chambers - floor) (characterized by their absorption coefficient at normal incidence).

This performance can be expressed in terms of deviation of measured sound pressure levels with respect to the theoretical levels obtained using the law of the inverse square of the distance (i.e. in terms of deviation from the spatial sound decay in a free field) by octave or 1/3 octave bands at specified locations.

For orders of magnitude deviations of measured sound pressure levels with respect to the theoretical levels obtained using the law of the inverse square of the distance up to 1.5 dB at frequencies below 630 Hz, up to 1.0 dB at frequencies between 800 and 5000 Hz, up to 1.5 dB at frequencies above 6300 Hz can be obtained in the case of testing stations in accordance with standard NF EN ISO 3745.

The prediction of the performance of acoustic test rooms in terms of cutoff frequency and of quality of the acoustic free field can be performed with the simulation software SILDIS®®.

The performance of an acoustic test room (anechoic or semi-anechoic rooms, including: aero-acoustic wind tunnels), in terms of sound insulation is very frequency dependent and is primarily related to airborne sound attenuation of the envelope (characterized by its sound reduction index) and also the effectiveness of the vibration control device (characterized by its filtration rate).

This performance can be expressed in terms of background nosie, i.e. in terms of A-weighted overall sound pressure levels or in terms of sound pressure levels in octave bands inside the test room.

For orders of magnitude, inside the testing room, A-weighted overall sound pressure levels of 10 dBA or less or sound pressure levels in octave bands of 0 dB or less can be obtained in the case of some performing testing facilties (always with a special construction).

the verification of the performance of acoustic test rooms (and their qualifications) can be conducted according to standard NF EN ISO 3745 Acoustics - Determination of sound power levels of noise sources - Precision methods for anechoic and semi anechoic rooms.