Development of measurement method for airborne sound emitted by personal watercraft

摘要

The personal watercrafts (PWCs) are operated in various ways; going around on certain course again and again, repeating acceleration and deceleration, or prolonged idling operation, for instance. The procedure of ISO 14509 has been applied in the traditional sound measurement for powered recreational craft. However, the standard is designed to measure the sound from the typical small crafts, on the assumption that they run straight in a constant speed. It is believed to be inappropriate to use this procedure for the measurement of PWC sound. In trying to establish the suitable procedure for PWC, evaluation by the auditory sense of 15 raters was carried out in parallel with the traditional sound pressure level measurement. As the candidate, four (4) measurement methods were employed in this test. Five (5) models of PWCs including modified crafts were used. Correlation between the results of traditional sound measurement and the auditory sense ratings was examined. Also taken into account was; reproducibility of the measurement, simplicity of the process, and capability of detecting the crafts modified by the users especially on the exhaust system. It was concluded that "Acceleration, Start at Bow on line" would be the most suitable method for evaluating the sound emitted by the PWCs. Then, the sound pressure level was measured by this method on eighteen (18) production models of PWC to identify the average and distribution of the measured data. This was in preparation for the future regulations in which the required limits of the PWC sound pressure level may be set by means of the measurements taken by this method.