Noise diagnostic and reduction of a scooter engine motorcycle

This paper presents an appropriate way to reduce the noise of a scooter engine motorcycle. In order to investigate the noise contribution of each engine component, the lead covering method was used to rank the noise source. With the noise spectra from measuring the pass-by noise and releasing the lead cover on each component sequentially, the correlations between specific frequencies and each component of the engine were found. Furthermore, the noise characteristics of all components were cataloged into the airborne noise and the structure-borne noise. In this research, it was shown that the airborne noise was usually coming from the air cleaner or muffler. Additionally, the power transmission mechanism like CVT or crankcase generated the structure-borne noise. Based on the diagnostic results above, some modifications of the motorcycle had been done, for example, isolating of the CVT-cover and the crankcase-cover, fixing of high density material at the air cleaner box and adding another layer around the exhaust pipe. For the pass-by noise measurement, it was shown that the noise level of the scooter was reduced by 2.5 dB(A). [Submitted For Noise ‘‘Outstanding Young Presenter’’ Paper Award.]