Near-Field Variation of Loudness with Distance

Abstract

The boundary element method was used to calculate the sound pressure levels at the two ears of an artificial head when a sound source was located in different directions and distances in the near field (within 1 m). Total loudness was then calculated by using a binaural loudness model. Results showed that, in the near field, total loudness does not always increase monotonically as the source distance decreases. As distance decreased (for bands with center frequencies above 2 kHz), generally loudness first decreased and then increased (creating a local minimum); and when the distance became very small, the loudness generally began to decrease again (loudness had a local maximum). The external surface model of the artificial head was explored computationally. Calculations confirmed that the local minimum and maximum were caused by scattering from the shoulders. The effect of the width of the shoulders on near-field loudness was also determined. Finally, psychoacoustic experiments were conducted on four subjects. Results confirmed the presence of a local minimum and maximum and supported the idea that scattering from the shoulders was the main cause.