Exhaust Sound Emissions from Classic and Vintage Motorcycles By Allan Johnson, B.S.A., M.Sc. 51 Market St., Georgetown, ON, L7G 3C4 Tel. 1(905) 877-1565 Email: afjohnson@sympatico.ca
Introduction Proposals have been made by the Canadian motorcycle industry association (MMIC) that a recently developed Society of Automotive Engineers (SAE) on-road motorcycle sound emission test, known as SAE J2825, be adopted by Canadian municipalities and their police forces in order to control motorcycle noise. Promotion of this roadside stop and test program raised questions amongst Canadian Vintage Motorcycle Group (CVMG) members as to whether their Vintage and Classic motorcycles would be able to pass such a test, since most of their motorcycles were manufactured before there were any required Canadian national numerical standards for allowable sound emission levels. A preliminary sound testing program on 52 Vintage and Classic motorcycles was conducted at the CVMG Annual Rally held at Paris, Ontario from June 18 – 20, 2010. The following is a report of the testing undertaken, the results obtained and some observations on the findings.
Materials and Methods The test instruments were those of the type used by the Canadian Motorcycle Association (CMA) and its member clubs for official testing of CMA and FIM sanctioned competition events requiring testing to the SAE J1287 protocol – a sound measurement testing protocol and standard for off-road motorcycles. The Digital Sound Level Meter used was an Extech model 407740, an Extech model 407744 Sound Level Calibrator was used as a 94 dBA calibration standard and where the motorcycle being tested did not have a tachometer, a Treysit sirometer placed on the bike’s saddle or rear fender was used to adjust the bike’s engine to 2000 or 5000 rpm. A small, marked wooden plate was used to gauge the correct 45 degree angle of measurement from the end of each silencer tip. It was removed before testing was done to eliminate any sound reflection from the plate, the 45 degree angle being then indicated by an appropriately placed narrow stick of soft wood radiating from below each exhaust outlet. A distance gauge to accurately place the sound meter 50 cm from the silencer tip on the 45 degree axis and at a height above ground equal to the silencer tip distance from the ground was constructed of soft wood so as to hold the sound meter in the correct position and alignment for each exhaust tip. This gauge also allowed the calibration unit to be rapidly deployed to check the sound meter calibration. The sound meter was used with the foam diffuser ball in place, except when calibrating the meter. Before the sound meter was placed in the testing position it was pointed away from the test bike to check that the background noise level was sufficiently low for a valid bike test to be conducted. The sound meter was steadied in place by hand while readings were being taken. If a motorcycle had two separate exhausts on opposite sides of the motorcycle the sound 1