Identification of Low-Frequency/Low SNR Automobile Noise Sources

This paper presents experimental investigations of determining and analyzing low-frequency, low-SNR (Signal to Noise Ratio) noise sources of an automobile by using a new technology known as Sound Viewer. Such a task is typically very difficult to do especially at low or even negative SNR. The underlying principles behind the Sound Viewer technology consists of a passive SODAR (Sonic Detection And Ranging) and HELS (Helmholtz Equation Least Squares) method. The former enables one to determine the precise locations of multiple sound sources in 3D space simultaneously over the entire frequency range consistent with a measurement microphone in non-ideal environment, where there are random background noise and unknown interfering signals. The latter enables one to reconstruct all acoustic quantities such as the acoustic pressure, acoustic intensity, time-averaged acoustic power, radiation patterns, etc. By combining a passive SODAR and modified HELS methods, engineers will be able to visualize all acoustic quantities. In particular, Sound Viewer enables engineers to extract target information with a negative SNR, for example, SNR < - 30 dB, and identify the precise locations of very low frequency (< 200 Hz) airborne and structure-borne sound sources with very high spatial resolution. Test results of Sound Viewer to analyze the engine sparkplug and muffler noise of an automobile sedan are presented.