Abstract
A low‐cost hemi‐anechoic laboratory for machine noise measurement is described. The special difficulties in qualifying tests of a hemi‐anechoic chamber were resolved using Moreland's procedure (NOISE‐CON 79 Proceedings, 365–372). These tests disclosed anomalies in the free field characteristics near 250 Hz, which were traced to even spacing of the sound absorptive wedges. These anomalies were reduced by splitting the space between wedges with absorptive dividers. The conclusion is drawn that regularities in wedge size or spacing must be particularly avoided when such test chambers are to be used for measurement of pure tones.
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