Abstract:

Tests were conducted with two sound-power reference sources (Bruel and Kjaer model 4204) in three different acoustical environments: half of a reverberation room (overall room dimensions 6.7x5.5x4.1 m), a large semi-anechoic room, and an indoor work space. Sound power (narrow band 136--6400 Hz) was determined using a semicircular array of eight sound-intensity probes rotated in steps of 20 deg (72 measurement positions) over a hemispherical integration surface, radius 1.52 m, with the source at the center. The floor base completing the surface enclosing the source was assumed to be rigid with zero normal intensity. Despite prevailing concerns about sound-intensity measurement in diffuse fields and reverberant spaces, it was found that there was quite close agreement between sound power determined in the reverberation room and sound power determined in the other two environments. Sound power determined in the semi-anechoic room and work space was found to be highly repeatable, within 2%. For both sources the sound power was about 10% less than the manufacturer's calibrated value. With the source outside the integration surface, sound power determined in the semi-anechoic room was two orders of magnitude less than sound power with the source inside. [See NOISE-CON Proceedings for full paper.]