Improvements to a small free-field listening room

An inexpensive free-field listening room (7 ft 8 in × 5 ft 9 in × 6 ft in high) was designed and constructed with walls made of 5 inch high acoustical foam wedges backed by $\text{1}\text{1}\text{2}$ inch foam and a $\text{3}\text{1}\text{2}$ inch layer of building-grade Fiberglas. The composite wall construction creates a rugged, non-irritating surface that is highly absorbent and relatively inexpensive. Deviations from the inverse square law are less than 2·3 dB above 500 Hz. Reverberation from a 40 ms 1000 Hz pulse is 31 dB below the original pulse. Results of these two tests are compared with measurements by Marsh et al. 1] in a room of similar volume having flat 4 inch foam walls.