Identification of ground and environmental effects to the pass-by noise testing of snowmobiles

Noise concerns regarding snowmobiles have increased in the recent past. Current standards, such as SAE J192 are used as guidelines for government agencies and manufacturers to regulate noise emissions for all manufactured snowmobiles. Unfortunately, the test standards available today produce results with variability that is much higher than desired. The most significant contributor to the variation in noise measurements is the test surface. The test surfaces can either be snow or grass and affects the measurement in two very distinct ways: sound propagation from the source to the receiver and the operational behavior of the snowmobile.;Data has been collected over two winter seasons and one summer season. A constant speaker sound source was used to observe how the test area behaved from a sound propagation perspective. The speaker was calibrated to a known sound power level using the comparison method provided in ISO 3741. Eight snowmobiles were evaluated using multiple pass-by techniques having the snowmobile in motion with stationary microphones at specified distances from the vehicle path. The snowmobile test matrix consisted of a steady state speed test at 35mph, an acceleration test following the SAE J192 procedure, an acceleration test following the SAE J192 with an entry speed of 30mph and an acceleration test following a Nordic proposed test method. The eight snowmobiles included a selection of representative marketed machines consisting of two machines from each of the manufacturers. Of the eight machines, one was selected as a control and tested during each test day. Three machines, including the control machine, were selected for on-board measurements in addition to the pass-by microphones to identify the snowmobile's behavior during the test. In addition to the speaker and snowmobile data, environmental and test surface metrics were also recorded for each test day.;With all of the collective data a statistical analysis was performed to understand the relationship between any measured metric to the overall response of the pass-by testing. One deliverable of this study is to provide data to support a rewrite of the SAE J192 standard in an effort to make it more repeatable. A significant component of the updated version of the test standard was to adjust the measurements on grass surfaces to appear more like measurements on a snow surface. The correction factor implemented into the standard was developed solely from this research effort. The updated version of the SAE standard will also be intended to be used to generate an ISO standard for the pass-by noise testing of snowmobiles. The development of the ISO standard will support the European Union's current noise directive and the data from this study is critical to that effort. Additional data analysis was completed to identify characteristics of each snowmobile tested and how the environmental and ground conditions affect the response of the machine during the pass-by event. The final data analysis and supporting conclusions show that it was possible to improve the variance of pass-by noise test results significantly from current levels.