DEVELOPMENT OF A SUITABLE ANECHOIC TREATMENT FOR THE ASD SONIC FATIGUE FACILITY

摘要

Results are given for a research program leading to the design of an anechoic treatment for the test chamber of the ASD high intensity sound facility. The acoustical requirements for 96 percent absorption coefficient at normal incidence for a frequency range of 50 7000 cps and for sound pressure levels up to 160 db and the mechanical requirements for a collapsible treatment presented novel problems in design. The require-ments were met by a treatment, six feet thick, composed of six layers of absorbing material irregularly spaced with the acoustical resistances per layer increasing from values for layers at the incidence sound side to higher values for layers near the room surfaces. Tests in the high intensity impedance tube facility designed for the program showed that the normal incidence absorption coefficient of the treatment was 96 percent or higher over most of the frequency range from 50 7000 cps at sound pressure levels from 130 to 160 db. Fairly satisfactory results were also obtained for a five layer treatment subsequently designed. Etched polyurethane foam supported by wire screens was initially chosen as the layer material because of its resistance to damage in small scale life tests at particle velocities corresponding to a sound pressure level of 160 db. In subsequent accelerated life tests in the siren facility at North American Aviation, Columbus, Ohio, there was no significant damage to a four by four foot specimen of material after 105 hours at sound pressure levels between 165 and 170 db except for failure of the supporting wire screens at about 78 hours.