In both fixed and rotary wing aircraft, the move toward lighter structures has resulted in an increase\nin structural vibration and interior noise. Porous materials have been proposed as acoustic\nabsorbers to reduce this noise. This paper discusses the development of equipment at the NASA\nGlenn Research Center for characterizing the acoustic performance of porous materials: a flow resistance\napparatus to measure the pressure drop across a specimen of porous material, and a\nstanding wave tube that uses a pair of stationary microphones to measure the normal incidence\nacoustic impedance of a porous material specimen. Specific attention is paid to making this equipment\nas flexible as possible in terms of specimen sizes need for testing to accommodate the small\nor irregular sizes often produced during the development phase of a new material. In addition,\ndue to the unknown performance of newly developed material, safety features are included on the\nflow resistance apparatus to contain test specimens that shed particles or catastrophically fail\nduring testing. Results of measurements on aircraft fiberglass are presented to verify the correct\nperformance of the equipment.
Loading....