Continuous-wave focusing of audible sound in a reverberation chamber using time reversal

Time Reversal (TR) is a technique used to focus of sound waves, using signals that are typically impulsive in nature, at a particular location in space and time. An impulse response is obtained between a source and a receiver, which records a record of the timing of various reflections as they arrive at a receiver. The TR technique involves broadcasting the time reversed impulse response from the source, which results in broadcasting of the various reflections in reversed timing order so that they all arrive at the receiver location at the same time. Previous work using TR of ultrasonic sine waves in elastic media [Anderson et al., Appl. Phys. Lett. 94(11), (2009)] showed that multiple sources must be used to achieve continuous-wave focusing. Here the number of sources needed to focus audible sine waves in a reverberation chamber is determined. The dependence of the number of sources on the frequency used, in relation to the room’s Schroder frequency, is also explored. A modal summation numerical model is also used to compare to experimental results.