Abstract: An enclosure for isolating noise sources composed of four walls and a ceiling, in which some or all of the sides and top consist of a muffler barrier including one or more air paths transverse to the principal direction of sound transmission through the structure. Various types of component muffler barriers are illustrated which include double leaf structures lined with sound absorbing material where the two leaves are disposed in spaced apart relation and include oppositely disposed air intakes and air exhausts to provide the intervening air paths. In one embodiment, components comprise corrugated panels of sound absorbing material disposed in face-to-face relation to provide multiple air channels.