Measurement of acoustic roughness

Use of CAT to measure acoustic roughness

The same CATs that are routinely used for reprofiling work are used to show that irregularities on sites comply with the requirements of EN ISO 3095 (“Measurement of noise emitted by railbound vehicles”) and EN 15610 (“Rail roughness measurement related to rolling noise generation”).  The CAT is widely used by acoustics consultancies, research organisations and vehicle suppliers for these purposes.

The CAT software includes standardised algorithms for “pit-and-spike” removal and “wheel curvature processing” and also the standardised presentational format for calculations of one-third octave spectra.

Successive measurements of a rail over 50m, showing irregularities in 30-100mm wavelength range (above) and one-third octave spectra (below) to a wavelength of 4m (limited by the length of the site).  Long wavelengths cannot be measured using straight-edge based equipment, but can be measured using the CAT.  For example, the CAT has been used by independent acoustics consultants to monitor longitudinal irregularities on Crossrail’s track in London, where there is a specification limiting longitudinal irregularities to wavelengths of 2m.

 

In the Figures above, measurements have been processed using the algorithms in EN15610:2009.  There is slight corrugation over the site.  The vivid red trace and dotted line on the exceedence graph are for the difference between the successive measurements.