(a) Microphone Location. The microphone used for testing an electromechanical or electronic siren shall be located 3.00 m ± 6 mm (9.8 ft ± 0.24 in.) from the edge of the siren horn or projector, in line with the siren axis, and at the same height as the siren. The microphone used for testing a mechanical siren shall be located 1.20 m ± 50 mm (4 ft ± 2 in.) above the test surface and 3.00 m 6 mm (9.8 ft ± 0.24 in.) from the nearest part of the siren.

(b) Microphone Orientation. The microphone shall be oriented in relation to the sound source in accordance with the instrument manufacturer's instructions. If the instruction manual does not include adequate information, a specific recommendation shall be obtained from the manufacturer.

(c) Personnel Location. During laboratory tests, technicians and observers shall remain outside the anechoic chamber. During field tests, persons other than the operator of the vehicle shall be positioned no closer than 3 m (9.8 ft) from the microphone or the siren.