[Code of Federal Regulations]

[Title 49, Volume 5]

[Revised as of October 1, 2005]

From the U.S. Government Printing Office via GPO Access

[CITE: 49CFR325.57]



[Page 14-15]

 

                        TITLE 49--TRANSPORTATION

 

                      DEPARTMENT OF TRANSPORTATION

 

PART 325_COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS

--Table of Contents

 

        Subpart E_Measurement of Noise Emissions; Stationary Test

 

Sec. 325.57  Location and operation of sound level measurement systems; 

stationary test.



    (a) The microphone of a sound level measurement system that conforms 

to the rules in Sec. 325.23 shall be located at a height of not less 

than 2 feet (.6 m) nor more than 6 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 4 feet (1.2 m).



[[Page 15]]



    (b) When the sound level measurement system is hand-held or 

otherwise monitored by a person located near its microphone, the holder 

must orient himself/herself relative to the highway in a manner 

consistent with the recommendation of the manufacturer of the sound 

level measurement system. In no case shall the holder or observer be 

closer than 2 feet (.6 m) from the system's microphone, nor shall he/she 

locate himself/herself between the microphone and the vehicle being 

measured.

    (c) The microphone of the sound level measurement system shall be 

oriented toward the vehicle at an angle that is consistent with the 

recommendation of the system's manufacturer. If the manufacturer of the 

system does not recommend an angle of orientation for its microphone, 

the microphone shall be oriented at an angle of not less than 70 degrees 

and not more than perpendicular to the horizontal plane of the test site 

at the microphone target point.

    (d) The sound level measurement system shall be set to the A-

weighting network and ``fast'' meter response mode.



[40 FR 42437, Sept. 12, 1975, as amended at 41 FR 10227, Mar. 10, 1976]