  We present a measurement of phonon propagation in a silicon wafer utilizing
an array of frequency-multiplexed superconducting resonators coupled to a
single transmission line. The electronic readout permits fully synchronous
array sampling with a per-resonator bandwidth of 1.2 MHz, allowing sub-$\mu$s
array imaging. This technological achievement is potentially vital in a variety
of low-temperature applications, including single-photon counting,
quantum-computing and dark-matter searches.
