1983 年 39 巻 4 号 p. 247-252
This paper describes the experimental results of degenerate parametric amplification which are performed in free field. The amplitude and phase controlled sound source consists of twelve tweeters, which radiates a 10kHz powerful pump wave and a 5kHz weak signal wave synchronously and collinearly. SPLs of both waves are 142dB and 122dB re 20μPa at 1m, respectively. The pump level is not so high as shock is formed. The obtained data confirm that the amplification really exists and the parametric signal periodically varies in amplitude with the initial phase of the weak signal having a period of π. These results are in identical fashion with the plane progressive wave in a tube except for π/4 phase difference. Changes in beam pattern with the phase are also observed. We discuss the farfield behaviors of the parametric signal by using the modified Pestorius'algorithm.