Feasibility study of localised active noise control using an audio spotlight and virtual sensors

Global control of sound at audio frequencies in large spaces is challenging and has been a sticking point for the development of active systems for noise control in areas such as factory floors or public spaces. Combining highly directional sound sources and virtual sensing techniques is proposed as a possible solution. Such a system would create localised zones of quiet that can follow an individual through a space. The application of a parametric array as a sound source is discussed in this paper. The parametric array creates an audible directional sound source due to the non-linear interaction of two ultrasound waves. A beamwidth of the order of a few degrees is possible at audio frequencies, however the sound levels produced are quite low. The properties of the source in regard to active control are discussed. Virtual sensing uses an array of microphones to predict the sound field at a remote point. It has been shown that active control of the sound field at a moving virtual error sensor is possible. The criteria for control performance in a 1D sound field using such a sensor are outlined. The advantages and disadvantages of the combination of these two advanced transducers for use in active noise control are discussed in this paper. Copyright © (2006) by the Australian Acoustical Society