MEASUREMENT OF VARIABILITY IN SOUND FIELD AUDIOMETRY DUE TO SUBJECT MOVEMENT

Sound field audiometry is used primarily for hearing assessment in you ng children and for functional hearing aid evaluation. It is important that measurements are accurate and reliable as they affect the manage ment of patients. Most clinics use a substitution method for calibrati on and, as a result, if the subject moves from the calibrated test poi nt, the sound pressure level (SPL) at the ears will vary as the sound field is very rarely uniform. This variation can result in inaccurate threshold estimation and increased test-retest variability. A commonly used method for evaluating the potential errors due to subject moveme nt involves measuring the variation in SPL, with respect to the test p oint, at six points around the test point. This method makes assumptio ns about the sound field which may not be valid and could lead to an u nderestimation of the variation present. The aim of this investigation was to assess the accuracy of this method. Measurements of variation were taken with a microphone and repeated with a head and torso simula tor (HATS) which was used to represent a test subject. The total degre e of variation indicated by these two methods was compared. The microp hone measurements indicated less variation than the HATS measurements. The differences were statistically significant but small in clinical terms. Assuming that the HATS is properly representative of the normal population, then this result indicates that simple microphone measure ments are acceptable for normal clinical practice but that higher qual ity measurements are desirable for critical work.