The effect of acoustic environment on the reliability of sound field audiometry

This study is one of a series designed to explore problems associated with sound field audiometry and to provide practical solutions to these problems. In this paper, we investigate the relationship between the acoustic absorptivity of a test room and the uniformity of the resulting reverberant field. The optimum absorptivity is not obvious on theoretical grounds because reverberant field testing relies on the presence of reflections from the enclosure surface. Measures of sound field uniformity were obtained from a room whose absorptivity was systematically varied. When measurements were made with pure tones, it was found that more complex sound fields, with deep but narrow troughs, are associated with reflective rooms. Frequency modulated tones lead to the most uniform reverberant fields when both room absorptivity and stimulus bandwidth are made as large as possible (the latter consistent with maintaining adequate frequency specificity). Even then, care should be taken in choosing the subject's position in the room when testing with low frequency stimuli.