  We present a user-friendly and versatile experimental technique that
generates sub-kilohertz sinusoidal oscillatory flows within microchannels. The
method involves the direct interfacing of microfluidic tubing with a
loudspeaker diaphragm to generate oscillatory flow in microchannels with
frequencies ranging from $10-1000$ Hz and amplitudes ranging from $10 - 600 \
\mu$m. The speaker-based apparatus allows independent control of frequency and
amplitude that is unique to the speaker's manufacturing specifications. The
performance of our technique is evaluated by Fourier spectral analysis of
oscillatory motion of tracer particles, obtained by particle tracking
velocimetry, as well as by comparing oscillatory flow profiles against
theoretical benchmarks such as Stokes flow in a square channel and Stokes'
second problem near a solid boundary. Applications that utilize both the
oscillatory flow and the associated steady rectified flows are demonstrated in
prototypical microfluidic configurations. These include inertial focusing and
mixing at low Reynolds numbers, respectively.
