Abstract Acoustic “breakout” and “breakin” through duct walls had, until the late 1970s, been a rather neglected topic of research, particularly in the field of heating, ventilating and air-conditioning ducts. Since then, interest has grown and many publications have appeared in which predictive methods have been reported. Research in this area, especially that which has been conducted over the past two decades, is reviewed in this paper. Efforts are made to identify the main physical processes involved and to present some relevant published data, rather than to give a finely detailed, comprehensive, account of this research. Some comments are made concerning the possible direction of future research.