Our team worked on a similar idea and the test phone speakers died pretty fast, probably 2 out of 3 within a month. The cause may be (1) we over-stressed them too much (2) they were cheap Samsung phones and (3) we used frequency around 20kHz to avoid annoying human users (this library seems to operate at 17+kHz at most). Our conclusion at the time was consumer speakers and microphones are not good enough. Would love to hear whether Quiet has the same issue.