When, in the progressive context of 1968 Paris, the architect Claude Le Goas was tasked with designing a music and dance school for the Communist-run suburb of Montreuil, he chose to express function through tectonics: stacked up like bottles in a rack, each of the lightweight metal practice rooms is acoustically independent of the rest. Forty-eight years after its 1976 inauguration, the Conservatoire de Montreuil has just reopened following a $7.9 million renovation-and-enlargement program led by the architect-scenographer Laurence Leroy, in partnership with ACTO Architecture.