Figure 2.

Laser Doppler vibrometer (LDV) and microphone measurements. (a) Schematic of the experimental set-up: the LDV measured vibrations of the right posterior tympanum, for sounds varying from +30° to −180° relative to straight ahead (0°). Sound pressure amplitudes were recorded with a microphone located 25 mm above the centre of the pronotum. (b) Example of the recorded stimulus, LDV and microphone responses. Amplitudes are given in arbitrary units; we were merely interested in normalized gains, measured in the linear range (see electronic supplementary material, figure S1). Because the order of stimuli was randomized, reflections from preceding stimuli (e.g. below the label ‘microphone’) hardly affected the measurements. (Online version in colour.)