Fig. 6. Prominent frequency notches in the echo spectrum (20-140 kHz) of different sized hollow hemispheres. (G) Notch frequencies displayed as a function of the reciprocal value of the radius. The shaded area indicates the frequency range of the echolocation call of Glossophaga soricina. (A-F) Spectral directional patterns and spectra (averaged over 13 single spectra from -60° to +60°) of six hollow hemispheres of different sizes. Note that the frequency scale is logarithmic. The arrows indicate the frequency notches. For tone gradation key in steps of 6 dB, see Fig. 4C.