This procedure should be used to determine the average sound pressure level that a snowmobile would generate during typical trail operation. It consist of averaging a steady vehicle speed SPL with a wide open throttle acceleration SPL together. A weighting is performed on both SPL prior to averaging. The weighting is based on a study on the vehicle speed, engine speed and engine load observed during typical trail use of a snowmobile.
There are currently two SAE standard for pass-by noise measurement of a snowmobile: - SAE J192 is a wide open throttle acceleration test. This condition is used a very small percentage of the time on modern snowmobiles with high specific output engine and the majority of acceleration event during trail riding happen at lower throttle openings. - SAE J1161 provides a sound pressure level at a constant speed of 24 km/h (15 mph) which is a relatively low speed compared to the average trail speed observed with modern snowmobiles and does not take into account the acceleration events during trail use. Therefore a new standard that would allow to determine an average sound pressure level observed during typical trail riding is appropriate. This level would consist of averaging a steady speed SPL and a wide open throttle acceleration SPL. Both level would be weighted prior to calculate the average. The weighting could be a fixed value or depend of the power to mass ratio of each vehicle and divide them into classes that would be used for the determination of the weighting factors.