Code of Maryland Regulations
Title 11 - DEPARTMENT OF TRANSPORTATION
Subtitle 14 - MOTOR VEHICLE ADMINISTRATION-VEHICLE INSPECTIONS
Chapter 11.14.07 - Noise Abatement Program
Section 11.14.07.11 - Sound Level Equipment Operation for Measuring Vehicle Noise
Current through Register Vol. 51, No. 6, March 22, 2024
A. The microphone of a sound level measurement system for all moving vehicle measurements for vehicles over 10,000 pounds GVWR and GCWR shall be located at a height of not less than 2 feet (.6m) or more than 6 feet (1.8m) above the plane of the roadway surface and not less than 3-1/2 feet (1.1m) above the surface on which the microphone stands. The preferred microphone height on flat terrain is 4 feet (1.2m).
B. Stationary Vehicle Measurements for All Vehicles.
C. Microphone Orientation. The microphone shall be pointed approximately straight upward so that the vehicle noise reaching the microphone from any point within the measurement site strikes the microphone at grazing incidence (parallel to the microphone diaphragm).
D. Meter Operation.