Fig. 8. Sound radiates from subjects in a relatively simple manner and a single amplitude decrement of variable width (degrees) and depth (dB) near 130° explains most changes. Plotted are amplitudes at 2, 4 and 8 kHz extracted from spectra of recordings obtained from subjects with a 5 mm beak gape. Measurements are averaged across each hemifield (0–171°) and are normalized relative to 0°.