Measurement of Exhaust Sound Levels of Stationary Snowmobiles
This SAE Recommended Practice establishes the test procedure, environment and instrumentation for determining the sound levels of snowmobiles in the stationary test mode. This test method is intended to provide an accurate measurement of exhaust and other engine noise and may be used to evaluate new and in-use snowmobiles to determine compliance with noise control regulations. Sound level measurements obtained with this test method are not intended as an engineering determination of overall machine noise. For this purpose, the use of SAE J192 is recommended.
This is a new test method, intended primarily to provide an accurate, repeatable, unbiased test methodology to assist in the enforcement of snowmobile noise regulations. It is emphasized that this test is a field type check, designed to assess only engine and exhaust noise, and does not purport to assess total snowmobile noise. For this purpose, SAE J192 should be used. Although many snowmobile regulations are written in terms of total snowmobile sound levels, i.e., SAE J192 sound emissions, long experience has shown that SAE J192 is impractical for field use. The intent of this document is to provide a go/no-go single number kind of test. A 1-to-1 correlation between total snowmobile noise, i.e., SAE J192 level, and stationary test sound, i.e., as measured by this methodology, is not expected. However, extensive testing has shown that if this procedure is followed, it can effectively identify vehicles whose noise level exceeds the regulatory level.
Because of this, it has been suggested that a 2 dB “tolerance” be added to any level selected as the cutoff sound regulation, when such level is evaluated by this methodology. This approach misconstrues the meaning of precision, as a range of precision is given by this, and other, SAE sound test documents. The 2dB range of precision, i.e., ±1 dB from the expected mean test
Sections 6.4 and 6.7 call for the test to be done at a steady 4 000 rpm ± 250 rpm, over a period of not less than 4 seconds. Some concern has been expressed that this period is long enough to cause damage to the snowmobile transmission belt. Section 6.4 requires that the microphone shall be located a distance of 4 m from the longitudinal plane of symmetry. Some authorities believe that 4 m is unnecessarily distant from the snowmobile, and introduces potential error from extraneous sources, ground plane reflection, etc. These authorities suggest measurements be made at a distance of 2 m. The task force solicits input on these two points, in particular.