On Minimum Audible Sound Fields

Abstract

The minimum audible field (M.A.F.) has been determined from data taken on 14 ears over the frequency range from 100 to 15,000 c.p.s. The observer is placed in a sound field which is substantially that of a plane progressive wave, facing the source and listening monaurally. The M.A.F. is expressed as the intensity of the free field, measured prior to the insertion of the observer. Similar data are presented for binaural hearing, over the range from 60 to 15,000 c.p s., obtained with 13 observers. At 1000 c.p.s. the average M.A.F. observed is 1.9 × 10−16 watts per cm2, corresponding to a pressure 71 db below 1 bar. Included are data showing how the M.A.F. varies with the observer's azimuth relative to the wave front. Another type of threshold data refers to minimum audible pressures (M.A.P.) as measured at the observer's ear drum. The differences obviously to be expected between M.A.F. and M.A.P. values are due to wave motion in the ear canal and to diffraction caused by the head. The M.A.F. data are discussed in relation to the M.A.P. determinations from several sources. Some possible causes of difference between the two, which are due to experimental procedure and may add to the causes already mentioned, are pointed out.

What Do Primates Hear? A Meta-analysis of All Known Nonhuman Primate Behavioral Audiograms

“…Though the differences are generally greater at frequencies <1 kHz, frequencies >8 kHz show the greatest variability in 3 cases and in 1 case frequencies between 1 and 8 kHz are most variable. The low-frequency (<1 kHz) results agree with the findings of Jackson et al (1999), but go further to show that all regions of the audiogram are affected by transducer type, similar to the conclusions reached by Sivian and White (1933). Packer (1983) suggested that using headphones may cause physiological noise partially to mask frequencies <1 kHz, resulting in auditory thresholds with higher sound pressure levels.…”

“…Both comparisons suggest that the conditioning procedure only marginally affects the auditory thresholds. Sivian and White (1933) first documented differences produced by different transducer types in their classic study on human hearing. They noted that thresholds produced by loudspeakers were consistently lower throughout the entire frequency range than those produced using headphones.…”

“…The only 2 human audiograms obtained in studies of nonhuman primates that are not included are those of Wendt (1934) and Semenoff and Young (1964). I exclude the audiogram from Wendt (1934) because the intensity levels in the study were calibrated using a human audiogram (Sivian and White 1933), and therefore their human audiogram is uninformative as to the sound pressure levels of their testing environment. I also exclude the audiograms from Semenoff and Young (1964), both for Homo sapiens and Macaca nemestrina, because their results are published in terms of root-meansquare voltage readings instead of SPL measurements.…”

“…I also examine the human threshold values but limited them to comparing transducer type because humans are never tested via negative reinforcement. I also consider 5 other human audiograms that researchers commonly use in comparisons of primate hearing: open and closed-field (Sivian and White 1933); Dadson and King (1952); free-field standard (ISO 1961); and closed-field standard (ANSI 1969).…”

“…4) that completed both tests. I adjusted the audiogram by Wendt (1934) via the ISO (International Organization for Standardization) human threshold values to calibrate the sound pressure levels instead of the values from Sivian and White (1933), originally used by Wendt. I did not consider the audiograms from Dalton (1968) and Pfingst et al (1975) because the same laboratories produced subsequent audiograms of Macaca mulatta based on larger sample sizes.…”