A single cylinder and two tandem cylinders configurations with longitudinal pitch ratios L/D = 1.75 and 2.5 were rigidly mounted in an open circuit windtunnel and a sound field was applied so that the acoustic particle velocity was normal to both the cylinder axis and the mean flow velocity. Tests were performed for a Reynolds number range of 5000 < ReD < 24000. The effect of sound on the vortex shedding was investigated by instrumenting the cylinders with pressure taps and hot-wire probes. These tests show that applied sound can entrain and shift the natural vortex shedding frequency to the frequency of excitation and produce nonlinearities in the wake. The lock-in envelope for the tandem cylinders is considerably larger than for the single cylinder. The lock-in range for the smaller tandem cylinder spacing (L/D = 1.75) was broader still than either the single cylinder, or the L/D = 2.5 tandem cylinder case.