From Longman Dictionary of Contemporary Englishsoundproofsound‧proof1 /ˈsaʊndpruːf/ adjective QUIETa soundproof wall, room etc is one that sound cannot pass through or into
Examples from the Corpus
soundproof• He used the space beneath his desk as a kind of soundproof booth.• So in 1954 Hebbs built a dark, soundproof cell at McGill University in Montreal.• Across a soundproof divider from the Kelleys will be Jenkins' witnesses: two lawyers and a woman described as his friend.• It was a soundproof, windowless room at the end of the corridor on the second floor.soundproofsoundproof2 verb [transitive] QUIETto make something soundproof→ See Verb tableExamples from the Corpus
soundproof• They also had to keep windows shut during services and soundproof the room.• The flat is soundproofed with 18 inches of concrete above and below. 