Fig. 9. Sound intensity above hearing threshold of pure-tone signals of 9 kHz and 18 kHz, as perceived by a female Neoconocephalus nebrascensis, over distance between sender and receiver. Data were calculated by assuming a signal amplitude of 110 dB SPL at 20 cm distance and using the measured data for the attenuation during sound transmission of pure tones (Figs 6, 7) and the hearing thresholds (Fig. 4). At approximately 1 m distance, both pure-tone signals are perceived at the same relative intensity (`break-even' distance; arrow).

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