soundproof

sound +‎ -proof

soundproof (comparative more soundproof, superlative most soundproof)

1. Not allowing sound through.

   The contestant was placed in a soundproof booth so he could not receive help from the audience.

• soundproofing

soundproof (third-person singular simple present soundproofs, present participle soundproofing, simple past and past participle soundproofed)

1. To make resistant to transmitting sound.

   We soundproofed the room so we couldn't hear the road noises; unfortunately we couldn't hear the fire alarm either.

   • 1980, Robert M. Jones, editor, Walls and Ceilings, Time-Life Books, →ISBN, page 114:

     Soundproofing a room may be as simple as sealing gaps around a door, or it may require rebuilding an entire wall or lowering a ceiling.