1967 年 23 巻 6 号 p. 433-441
This paper describes the acoustic design and characteristics of the sound echo chamber, which was recently constructed and taken into service by NET-TV Co. Features of the chamber:(1)In order to be entirely free from outside noise and vibrations, the bulding is isolated from other buildings and the room itself is supported by anti-vibration rubbers. The plan view is shown in Fig. 3. (2)The mortar-walled room has rectanglar shape and 86m^3 in volume. The ratio of length, width and height is fixed to 1:2^<2/3>:2^<1/3> so that a uniform distribution of the axial modes with respect to frequency may be attained. (3)Reverberation time of medium and high sound frequency is adjusted by up and down motion of a curtain hanging in the middle of the room. Adjustment of reverberation time of low sound frequency is done by varying the position and surface area of the motor-driven glass wool blocks placed at the three corners of the room. These adjustments are remotely controlled from the studio control room. Details of variable absorbers are shown in Fig. 5 and Fig. 8. (4)Various tones of echo are obtained by the combination of the places and mixing of four microphones available. (5)In order to improve the diffusion condition of the room, four boards for each of the sizes 910×910mm and 910×1820mm are hung. In order to limit the booming in low sound frequency region, two small pocket resonators having resonace frequencies of 50c/s and 80c/s are placed at the corners. (6)Reverberation characteristics are shown in Fig. 13, 14 and 15 respectively.