Abstract
Introducing acoustic radiation ratio η_r which is ratio of acoustic power to mechanical power of a vibrating plate, frequency dependence of acoustic radiation from circular plates are theoretically studied. η_r has a deep through between the very low eigenfrequencies and the coincidence frequency. When the diameter decreases or the thickness increases, the depth of the though decreases. In general, when the plate becomes thin, the deflection becomes large, and the noise increases. However, in noise reduction, it is important to make use of the through of η_r, because, at some frequency range, a thin plate has smaller η_r than a thick plate.
