He Sells Silence -- In their sound-proof laboratory, Douglas Smart and his assistant, Ken Shearor, are here seen at work measuring the revorberation time of the test chamber using a logarithmic cathoderay oscilloscope. Restoring quiet in a noisy world is the unusual occupation of Mr. Douglas Smart. As one of the few architectural acoustical engineers in Britain, he often finds himself a keeper of the peace. Once he was called in to treat a council house after rebellious tenants, demanding privac