Should be possible to generate acoustic Čerenkov radiation using an inhomogenous medium interface and harnessing the coherent generation of diffraction modes.
I'd imagine one could start using a rotating subwoofer (modulated fan blade attack angles and some metamaterial for the blade themselves).
Effectively the interface curvature/inhomogenuity provides energy-pumping resulting in lasing.
cf. [optical] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3810664/