Acoustic retroreflectors in architecture: From incidental cases to focusing designs

Retroreflective acoustic treatment of architectural spaces can concentrate early-reflected sound onto the respective arbitrarily located sources. Typically, this is achieved by arrays of corner reflectors (CRs) or cube corner retroreflectors (CCRs). Still greater sound concentration can be achieved by focusing retroreflectors—achieved by curving the CRs’ or CCRs’ faces. This paper reviews physical instances of and experiments with such retroreflective treatments in buildings. Incidental cases include building facades, Indian stepwells, and arguably the original Concert Hall of the Sydney Opera House. Designed cases include both non-focusing and focusing installations, including experiments with room and ceiling treatments. Implications of such treatments on room acoustical design are discussed.