Two‐ear correlation in the statistical sound fields of rooms

The normalized correlation function R( f ) connecting the signals at the left and right ears was measured in a reverberant room as a function of frequency. Head diffraction effects are made evident by comparing these data to the correlation function predicted and observed for two microphones separated by a headwidth (15 cm) of space and moving in the same room. In contrast to the familiar two‐mike sinc(δ) correlation (δ=kd), head diffraction gives a two‐ear correlation function which is well described by sinc(αδ)/[1+(βδ)⁴]^1/2, where α=2.2 and β=0.5. The dominant effect of head diffraction is to lower  f_D, the decoupling frequency [first zero of R( f )] to 500 Hz, about half the no‐head value. The denominator in the fitted correlation function represents the near total independence of the signals at the two ears above  f_D. Thus with head diffraction the variance in a paired‐mike room averaged pressure amplitude estimate at around 500 Hz is already as small as that obtained sans head only at frequencies above 1200 Hz.