Fig. 1. Average amplitude spectra of digitized anemometer responses to a suprathreshold (15 m s^-2 (RMS) at the source) 50 Hz vibrating sphere for four different flow velocities (0, 2, 4 and 8 cm s^-1). Each amplitude spectrum represents the average of four spectra, each obtained from repeat measures of the time-waveform at a given flow velocity. (A) Amplitude spectra from normal, experimental conditions. (B) Amplitude spectra from control conditions in which the flow-producing impeller blade was removed from the drive shaft, but the drive shaft motions remained coupled to the water for different motor speeds. Note that 60-cycle electrical noise is inexplicably more prominent for the 8 cm s^-1 flow condition in A.