The perception by normal hearing persons of intensity fluctuations in narrow band stimuli and its implications for sound field calibration procedures

Narrow band complex stimuli (such as F.M. tones, A.M. tones, damped wavetrains and narrow band noise) are used in sound field testing to overcome the effects of standing waves in the test enclosure. All such stimuli have a fluctuating intensity when they reach the ears of the person being tested. The temporal integration model proposed by Plomp and Bouman (1959) is suggested for use in the calibration of such fluctuating stimuli. Experimental data are given which show that when this is done, the threshold for pure tone stimuli may be inferred from measurements made with the complex stimuli. This equivalent pure tone threshold can be most accurately determined if the complex stimulus contains only small intensity fluctuations, or if the fluctuations occur at a rate sufficiently fast that the high intensity portions are not fully perceived by the ear. A method of calibration for such stimuli is suggested which involves reading the peak deflection of a standard sound level meter set to its 'rms-fast' mode.