A quick and practical experimental method for separating wheel and track contributions to rolling noise

A rapid and inexpensive experimental method for the breakdown of wayside rolling noise into direct and indirect wheel and track components has been developed. "Direct" in this context refers to the sound radiation from the outside of wheel and track. "Indirect" refers to sound radiation from inside wheel/track parts which is first reflected in the running gear, vehicle subframe and ballast before being radiated to the wayside. The separation method requires simultaneous measurements with a close range highly directive parabolic reflector microphone and a microphone on the track bed. The method gives the sound power for the above-mentioned components in 1/3-octave bands. For validation, synthesized wayside sound pressure time histories in 1/3-octave bands are compared with measured ones at 5 and 25 m distance from the track. The acoustic model for the source separation also allows a rough assessment on the efficiency of noise reduction measures like shielding, wheel damping, bogie absorption, etc., to be made. The method is demonstrated on pass-bye of X2000 trains and the potential benefit of damping, absorption and shielding is discussed. (C) 2000 Academic Press.