(a) Mounting of Test Sample. Mechanical sirens shall be mounted on a vehicle for open field testing. Electromechanical sirens and electronic siren speaker assemblies shall be mounted on a test fixture secured to a turntable in an anechoic chamber as follows:
(1) Height Above Turntable. The height, measured from the lower edge of the siren stator housing of electromechanical sirens or from the lower edge of the speaker bell of electronic sirens to the face of the turntable, shall be 1.2 m ± 76 mm (4 ft ± 3 in.).
(2) Distance from Surface of Test Area. Sirens shall be located as far from the walls of the anechoic chamber as practicable.
(b) Power Supply. The electrical power supply for testing electromechanical and electronic sirens shall be as follows:
(1) Electromechanical Sirens. The power supply for the electromechanical siren under test shall be a battery of the correct rated voltage with a cold cranking performance rating at -18° C (0° F) of from 550 A to 620 A and a rated minimum reserve capacity at 26.7° C (80° F) of 140 min. The battery shall be at full charge and in good condition at the start of the test.
(2) Electronic Sirens. The power supply for electronic sirens shall be a well-filtered, voltage-regulated power source meeting at least the requirements of SAE J823c, January 1975. The voltage measured at the power supply output terminals with the siren operating shall be as follows:
Rated voltage
Test voltage for sound level
Test voltage for wattage
6
6.5
7.2
12
13.6
15.0
(c) Sound Level Meter Operation. The sound level meter shall be operated in accordance with the instrument manufacturer's instructions and as follows:
(1) Sound Level Meter Setting. The sound level meter shall be set for the A-weighted network and fast response.
(2) Octave Band Analyzer. The octave band analyzer shall be operated to determine the octave band containing the maximum sound output in each siren mode.
(3) Calibration Check. An external calibration check shall be made before and after each period of use and at intervals not exceeding 2 h when the sound measuring instrument is used for a period longer than 2 h.
(4) Ambient Sound. Measurements shall be made only when the A-weighted ambient sound level, including wind effects and all other sound sources, is at least 10 dB(A) lower than the sound level of the siren.
(d) Siren Operation. The mounted siren shall be operated to determine the sound level output under each function at the established test points as follows:
(1) Electromechanical and electronic siren speakers shall be rotated from at least 50 deg left to 50 deg right of the center of the siren axis at a constant speed during the siren operation.
(2) Mechanical sirens shall be tested when mounted on a stationary vehicle and operated at speeds equivalent to a road speed of 30 to 80 km/h (19 to 50 mph) to determine maximum noise output straight ahead of the vehicle (the vehicle may be mounted on rollers). The speed at which maximum sound level occurs shall be continued while the microphone is moved from 50 deg left to 50 deg right of the center of the vehicle axis.
