From René Lapalme
Perhaps there is a better alternative to using a high-powered propane cannon or gunshots for mapping caves with sound waves (4 June, p 26).
As a graduate student in the acoustic building division of Canada’s National Research Council in Ottawa, I took part in an evaluation of the acoustic quality of two nearly identical theatres. For this we used both gunshots and computer-generated chirps, which are intense, pre-calibrated sounds with a controlled frequency.
Chirps produced reflected sounds that were easier to analyse than those from gunshots.
Chécy, Loiret, France
