Projects

Controlling the sound field within enclosures is one area of interest for the ANVC group. The acoustic potential energy within the acoustic space provides the most suitable cost function to achieve global noise control. In practice it is very difficult to measure the acoustic potential energy so a large number of microphones are often used instead to provide an estimate of the potential energy. This approach has its obvious draw backs. Clearly such an approach may not be effective if the microphone is located in an acoustic node (a region of very low sound pressure level). Researchers at Penn State University found that this limitation may be overcome by measuring the particle velocity and the acoustic pressure. By minimising the velocity, the kinetic energy is minimised much like the potential energy is reduced by minmising acoustic pressure. If the signals for the velocity and pressure are combined with correct weighting then it is possible to minimise the acoustic energy density. Work undertaken by both the group and previous researchers has shown that minimising the acoustic energy density (rather than acoustic pressure) improves global attenuation in enclosures. A 3 axis energy density probe has been built by the ANVC group to be used as an alternative sensor to microphones. The unit has been designed to operate in the range of 50-1000Hz. A larger model is being built to operate between 25-500Hz. The velocity is calculated via the pressure gradient using simple analogue circuitry. The electronics allows the individual microphones to be calibrated. In addition, the electronics enables alternative microphone spacings to be used so that the same unit can accommodate different probes.

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