Sound field measurement tutorial. Working Group on Sound Field Calibration of the Committee on Audiologic Evaluation...

Although there are no standards or guidelines for sound field testing, it is recognized that such testing is an integral part of audiologic evaluation. This paper has reviewed some of the problems in sound field testing, as well as possible solutions to those problems. This review may be summarized as follows: 1. The environment in which sound field testing is conducted is an integral part of the test procedure; thus, the ambient noise and reverberation characteristics of the test room must be known. The test room must have ambient noise levels below the level at which the test signals will occur. 2. The listener must be seated so that the SPL of the test signal is known at that listener's pinna. Thus, care must be taken to exclude anything between the ear of the listener and the loudspeaker, and the height of the loudspeaker must be appropriate for the listener. (Note: If the loudspeakers are raised or lowered, it may be necessary to recalibrate.) The near/far field and direct/reverberant field boundaries should be identified and the listener positioned between those two boundaries. 3. The acoustic properties of the test signal must be defined clearly. An FM signal is best for assessing threshold of hearing. The examiner should measure the SPL and verify the spectral characteristics of the signal. The frequency of calibration measurements should be identical to that used for earphones, generally once every 3 months. Finally, it is important to understand the potential interaction between the test environment, the signal, and the listener when testing in the sound field. If the problems are understood and compensations are made it should be possible to obtain reliable and useful auditory information in the sound field.