He Sells Silence -- Douglas Smart uses a portable sound-level meter while his assistant, Ken Shearer, and Miss Joyce Thompson carry out articulation tests in their sound-proofed board room. 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 privacy, had refused to pay rent. I