Incidental acoustic retroreflection from building façades: Three instances in Berkeley, Sydney and Hong Kong

Abstract

This study investigates acoustic reflection from three building façades, each of which forms an array of corner cube retroreflectors. The façade of Latimer Hall (Berkeley, USA) has deep rectangular balconies that typically provide 56 simultaneously visible retroreflective elements; the Ainsworth Building (Sydney, Australia) has a sawtooth façade with 95 simultaneously visible corner cubes; and a façade of the Murray Building (Hong Kong) has 280 simultaneously visible recessed retroreflective windows. Acoustic measurements using a collocated loudspeaker and microphone are used to observe the retroreflection at two positions on each site. Results show a cluster of reflections corresponding to the façade, which stand out from the general reflection pattern, especially at high frequencies. Measured reflected energy levels are greater than geometric predictions, especially at low frequencies, while finite-difference time-domain simulation of one of the sites yields results closer to the measurements. This study sheds light on a distinctive, but not rare, façade acoustic reflection phenomenon, which can play a role in understanding urban acoustic issues, and also may find application in other areas of architectural acoustics where reflection of sound back to the source would be beneficial.