The Study Of Some Problems In The Application Of Acoustics

In the dissertation, some problems in the application of acoustics have been studied.(1) The basic theory treating steady-state acoustic radiation with near-field acoustical holography has been introduced. With the help of the near-field acoustical holography, the vibration characteristics of the irregular objects, the one-tone chime stone and the two-tone chime stone have been researched and some meaningful results gotten. 1) For the one-tone chime stone, there are two main vibration modes, which make up the base of sound produced by the instrument. On the fundamental mode, the strongest vibration is on the curved interface of the two parts and the vibration at two poles very weak. On the second harmonic vibrational mode, the strongest vibration is at two poles and the vibration in the middle is weak. At the wider side, there is a contrary phase vibration, which is twisted to the longitudinal vibration. 2) As for the two-tone chime stone, although the two excited points and the frequencies are different, the vibration modes are similar. The vibration in the middle is strong and two poles weak. There are two node lines in the longitudinal direction, which is similar to (0,2) mode of rectangle plate.(2) With time-frequency analysis, the frequency characteristics of sound and the vibrational modes of a two-tone Chinese Peace Bell have been studied. 1) For the reason of decay of high partials, the instantaneous averaged frequency of the sound radiated from the bell decreases from 220Hz to 160Hz within 3 seconds, then waves in the range of 160Hz to 170Hz. So the subjective pitch of the bell is not at the fundamental 68Hz but 160Hz or so. The reason of the disparity is that the high partials with great amplitudes, especially 222Hz, decay not as fast as expected and the transition time to a pure sound of 68Hz is too long, even can't become a pure tone. 2) The research on its vibrational modes shows that when the bell is struck at the center striking point, not only the vibration of mode (2,0)a is excited, but also...