An Investigation into the Microstructure of the Low Frequency Auditory Threshold and of the Loudness Function in the near Threshold Region

Abstract

The minimum audible field (MAF) is the sound pressure level at the threshold of audibility. The MAF threshold contour clearly demonstrates the variations in sensitivity of the auditory system with frequency. This frequency dependent sensitivity is also apparent at higher intensities, the importance of which is demonstrated by the extensive use of the dB(A) weighting in noise measurements. The sparse data available on low frequency auditory thresholds, and on the subjective effects of low level low frequency noise in the threshold region, indicated that a study of low frequency thresholds and near threshold equal loudness contours would fill a significant gap in the understanding of sound perception in this frequency range. This investigation demonstrates the existence of wide variations in individual sensitivity to low frequency sound. The diversity in auditory response to low frequencies between individuals should therefore be a prime consideration in low frequency noise control.

The effect of the helicotrema on low-frequency loudness perception

“…On the other hand, Frost (1987) found in one subject microstructures that show a distinct dip at 40 Hz in agreement with the present observations. However, no cases of a clear step region appear in Frost's data.…”

“…With this in mind, a review of LF-psychoacoustical data by Møller and Pedersen (2004) did not reveal any convincing behavioral homologue to the typically observed step region in the METF, neither in the hearing threshold, nor in ELC data. Whilst an irregularity, or an increased variance can occasionally be seen in the expected frequency region (e.g., Frost, 1987;Watanabe and Møller, 1990), many data have insufficient frequency resolution. Furthermore, the frequency of the resonance might vary individually so that the process of averaging over many subjects might have led to a cancelation of this feature in most studies.…”

Investigation of environmental low-frequency noise

“…Therefore, only people characterised by high sensitivity to low-frequency sound and living in quite rural locations can be affected. Nevertheless, even though a number of such people is relatively small, these cause quite specific physiological and legal aspects related to individual perception of lowfrequency noise [24], in particular the increased annoyance of tonal components [25]. We did not touch these aspects in the present work, concentrating on physical mechanisms of the low-frequency noise.…”

Failures in the System for Dealing with Low Frequency Noise

“…Again training is responsible for this lack of understanding of the wide variability in thresholds at the lowest frequencies [7], and for failure to take into account the current degree of uncertainty as to how the brain interprets LFN including infrasound.…”