He Sells Silence -- Douglas Smart and an assistant test a ventilator duct in their laboratory. 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. In his 20 years' experience, Mr. Smart, an Aberdonian, has muffled everything from the cry of ne