The 'Steering Committee for the sound level reduction in Motocross and Enduro' was created in February 2008, with the support of the Manufacturers and Youthstream, to define a new method by which to control the sound level of competition motorcycles.
The primary aim of this search was to find a method which accurately links the amount of noise emitted by a static motorcycle during a sound test with the amount that can be heard in the 'real world' during track activity.
After testing 40 Motocross and Enduro machines, the Sound Reduction Committee found that the existing method of sound measurement was highly inconsistent; a bike which was 'quiet' during the static test could turn out to be 'noisy' when on track and vice versa.
The committee found that this could lead to 'unfair assessments' - where a machine might be above the sound limit during the static test but below the sound limit on track, or below the sound limit during the static test but above it on track - of between 40-50%.
A new sound measurement method was therefore sought which would accurately link static test noise and 'real world' track noise.
The new system, provisionally known as the '2 metre Max' method (a name which will be modified in 2009) uses the same sound control methods and instruments as those at present.
However, it claims to reduce 'unfair assessments' between static test results and track sound to just 5%.
The system works by placing the microphone two metres behind the contact patch of the motorcycle's rear wheel and 45 degrees (pictured) from the centreline of the motorcycle. The microphone sits 1.35m from the ground and points towards the exhaust. The microphone unit is tilted at an angle of 45 degrees (up or down).
The test takes place once the engine and exhaust have been warmed up and using the same engine mapping as when on track. With the gearbox in neutral, the engine rpm is quickly raised from idle to maximum rpm by a sudden opening of the throttle (within one second), then returns to idle speed after a sudden release of the throttle.
Further work to refine the new method will be carried out during 2009. The aim is then to systematically introduce the new method from the 2010 season.