(a) The microphone of a sound level measurement system that conforms to section 451.2 of this Title shall be located at a height of not less than two feet (0.6 m) nor more than six feet (1.8 m) above the plane of the roadway surface and not less than 3 1/2 feet (1.1 m) above the surface on which the microphone stands. The preferred microphone height on flat terrain is four feet (1.2 m).

1. (1) When the sound level measurement system is hand-held or is otherwise monitored by a person located near its microphone, the holder must orient himself relative to the highway in a manner consistent with the recommendation of the manufacturer of the sound level measurement system.
2. (2) In no case shall the holder or observer be closer than two feet (0.6 m) from the system's microphone, nor shall he locate himself between the microphone and the vehicle being measured.

(b)