1971 年 27 巻 3 号 p. 153-162
This paper describes the criterion of the perceptibility of the echo which is necessary for simply detecting the echo due to multi-reflections by the observation of echo time diagrams The perceptible limit of the echo is given by a single curve where the ordinate is the listening sound level and the abscissa is the time delay of the reflection. Then, (a) the inclination of the perceptible time level characteristic of the echo is given, (sound pressure level)/ (300 milli-seconds), (b) in the case of the reflection, where the level is larger than that of the perceptible limit existing, the masking of the echo begins from that point again, (c) the perceptibility of the echo is concerned with the projecting level over the perceptible limit. The projecting level in which echoes are slightly audible is within 1. 5〜4dB high in the range of the frequency of 500-2000 Hz.