Acoustical studies on p′i‐p′a and cheng

Abstract

Improved holographic interference patterns of the vibrational modes of the front plate of a p′i‐p′a will be shown. Most of the modes lie below 2000 Hz and those having larger amplitudes of vibration lie between 320 Hz to 1300 Hz. Vibrations of the front plate due to plucking of the strings have been studied. It is found experimentally that any one of the three strongest plate modes can be excited when the fundamental frequency of the plucked string is equal to or is a subharmonic of the frequency of that mode. The p′i‐p′a sound generated by plucking the string is picked up by a sound level meter and the Fourier components are obtained by using a digital storage oscilloscope coupled to an Apple II computer. Because of the lack of an anechoic chamber, the sound level meter was placed not more than 1 m from the front plate. Even with this limitation, it was discovered that the sound pressure levels associated with different mode patterns decreased, with increasing distance, at different rates. This seems to mean that listeners at different distances from the player would hear music of different tone quality. Holographic vibration patterns and frequency response curves were also obtained for another Chinese musical instrument, the cheng. Efforts were made to identify various wood or air resonances. The cheng is a much larger instrument than p′i‐p′a, and both its front and back plates can vibrate strongly.Improved holographic interference patterns of the vibrational modes of the front plate of a p′i‐p′a will be shown. Most of the modes lie below 2000 Hz and those having larger amplitudes of vibration lie between 320 Hz to 1300 Hz. Vibrations of the front plate due to plucking of the strings have been studied. It is found experimentally that any one of the three strongest plate modes can be excited when the fundamental frequency of the plucked string is equal to or is a subharmonic of the frequency of that mode. The p′i‐p′a sound generated by plucking the string is picked up by a sound level meter and the Fourier components are obtained by using a digital storage oscilloscope coupled to an Apple II computer. Because of the lack of an anechoic chamber, the sound level meter was placed not more than 1 m from the front plate. Even with this limitation, it was discovered that the sound pressure levels associated with different mode patterns decreased, with increasing distance, at different rates. This seems to ...