Coincidence Effect of a Finite Plate

Abstract

The coincidence effect of a thin circular plate clamped at its edge in an infinite rigid baffle is discussed. It is shown theoretically that the radiation efficiency c for the finite plate displays a peak just above the critical frequency. This phenomenon was verified by the experiments. When the finite plate is vibrationally excited, the natural frequency (the pth mode) close to the forcing frequency has the greatest influence on the sound radiation. Therefore we can assume that 0= ζ_pp, whereζ_pp is the self-radiation resistance of the pth mode. The integral expression formulated forζ_pp shows that the vibration energy is transformed into sound energy radiated through the filter which possesses the sound radiation characteristic. The theoretical analysis of this equation reveals that the coincidence effect of the finite plate occurs at the frequency which simultaneously satisfies the two conditions ; the resonance excitation and the highest effective transformation from the vibration to the radiated sound.