Using Coherent Averaging with time-varying conditions to remove room reverberation from transducer measurements

Abstract: The use of coherent averaging in building acoustics is familiar to those who use deterministic signals (e.g. MLS) as the basis for their measurements. The primary concern is to achieve a sufficient signal to noise ratio so that results relate to the system being measured rather than unrelated noises. The technique requires conditions to be unchanging with time but coherent averaging can be used to advantage in situations where conditions are purposefully rendered time-varying. It is possible to select or reject contributions to a measurement by choosing some transmission paths to be time invariant and making others – ones we wish to remove from the measurement - varying. This presentation looks at using coherent averaging to measure transducer responses with high precision without using either an anechoic chamber or a time-windowing technique. Also we consider whether any particular deterministic signal – e.g. Farina’s log sweep – is more advantageous for this application.