Division 3.1 Audible warning devices must preferably be tested in an anechoic environment. They may alternatively be tested in a semi-anechoic chamber or in a cleared outside space. In this case, precautions must be taken in order to avoid reflections off the ground in the measuring area, e.g. by providing a number of absorbent screens. It must be checked that the spherical distortion is no more than 1 dB within a hemisphere having a radius of at least 5 m up to the maximum frequency to be measured, this mainly being in the direction of measurement and at the height of the device and microphone. The ambient noise must be at least 10 dB lower than the sound pressure levels to be measured.F1

United Kingdom Repealed