## Noise emission from snowmobiles

Hans G. Jonasson

SP Technical Research Institute of Sweden

Box 857

SE-501 15 Borεs

hans.jonasson@sp.se

Four different snowmobiles have been tested using different methods. The operating conditions have been accelerating, cruising and stationary and two different measurement distances and two different microphone heights have been used. The maximum pass-by sound pressure levels were measured in both 24 km/h and 50 km/h using both time-weighting F and S. In addition the acoustic impedance of the snow and grass covered ground was determined. The measurements were also carried out in frequency bands and these results were used to put up an acoustic source model of the snowmobile, which was then used to calculate the acoustic ground effect for propagation over different distances and ground surfaces.

The most important conclusions of the measurements and theoretical calculations are:

All snowmobiles tested failed to meet the American requirements for maximum pass-by sound pressure level during acceleration;

time weighting S used by SAE-standards yields around 2 dB lower measurement values than time-weighting F normally used for road vehicle testing;

type approval measurements should be carried out on snow. The snow depth is not very critical as long as it exceeds 7,5 cm;

selection of measurement distance and time-weighting is not very critical as long as the limit values are adjusted accordingly;

grassland may influence the operating conditions and should not be used for type approval measurements;

operating conditions should be both cruising and accelerating. The reference speed for acceleration is not critical. However, when cruising, 50 km/h makes much more noise than 24 km/h;

subtraction of two dB from the measured value as in SAE J192 is not compatible with the European Directive on noise emission from equipment for use outdoors.