Applications of the Acoustic Centre
This paper focuses on uses for the acoustic centre concept, which in this paper represents a particular point for a transducer that acts as the origin of its low-frequency radiation or reception. The concept, although new to loudspeakers, has long been employed for microphones when accurate acoustic pressure calibration is required. A theoretical justification of the concept is presented and several calculation methods are discussed. We first apply the concept to subwoofers, for which the acoustic centre is essentially a cabinet dimension away from the centre of the cabinet. This has an influence on its radiation pattern in a normal room with reflecting walls. A second application that we consider is the effective position of a microphone, which is necessary if it is to be used for accurate calibration of acoustic pressure. A final application that we consider is the effective position of the ears on the head at lower frequencies. Calculations show that the acoustic centres of the ears are well away from the head, and the effective ear separation is larger than expected. This has implications for the human localization mechanism. Measurements on a Kemar mannequin show that the separation is even larger than expected from the calculations, and most of this can be understood, but the measurements at the lowest frequencies are somewhat uncertain.
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