DISCUSSION OF ECHO,
FOREIGN TECHNOLOGY DIV WRIGHT-PATTERSON AFB OHIO
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The author discusses basic principles, structures, and uses of anechoic rooms, with emphasis on the operating features of an anechoic room set up at Nanking University in 1964. Anechoic rooms with six surfaces lined with wedge-shaped units are double walled to exclude disturbing sounds. Foundations with spring shock absorbers are used, and ditches are dug around the outer wall to secure high shock resistances and also an acoustical absorption coefficient close to 100. Weight support is made possible suspending a mat of crossed iron wires or nylon cords over the center of the floor. The room has more than 3400 wedges composed of Chinese-made glued glass fibers. More than 99 and 99.9 of incident energy is absorbed at frequencies above 70 and 200 Hz, respectively, when the dimensions of the wedges are as follows overall length, 1 m area of the bottom surface, 40 sq cm and air cavity, 15 cm.
- Test Facilities, Equipment and Methods