LDV on a Stereo Speaker
Laser Doppler Velocimetry (LDV) was applied to the flow at the exit of a stereo speaker. Data from the experiment can be seen to the right.
Water droplets from an ultrasonic humidifier were used as the seed particles. The speaker was contained within a Plexiglas box, seeding was introduced, allowed to settle, and then phase-locked LDV measurements were taken at approximately 2 cm from the center of the speaker exit. The frequency of the emitted tone was approximately 22 Hz.
In the plots, channel 1 represents the axial direction, and channel 2 represents the radial direction. Notice that the air velocity oscillates between approximately -1.2 m/s and +1.2 m/s in the axial direction, but remains centered at 0 in the axial direction. The real-time plot of channel 1 velocity shows very clearly the phase-locked nature of the measurements, in which the time is reset for each trigger (22 Hz), and each batch of data is overlaid on the same axis. In addition, the power spectrum was performed based on the Slot Method, which takes the first data point from within each evenly spaced slot, and Uses it to compute the spectrum. It then assumes the data points are evenly spaced at the Slot interval.