Optimal virtual sensing for active noise control in a rigid-walled acoustic duct

Abstract

The performance of local active noise control systems is generally limited by the small sizes of the zones of quiet created at the error sensors. This is often exacerbated by the fact that the error sensors cannot always be located close to an observer's ears. Virtual sensing is a method that can move the zone of quiet away from the physical location of the transducers to a desired location, such as an observer's ear. In this article, analytical expressions are derived for optimal virtual sensing in a rigid-walled acoustic duct with arbitrary termination conditions. The expressions are derived for tonal excitations, and are obtained by employing a traveling wave model of a rigid-walled acoustic duct. It is shown that the optimal solution for the virtual sensing microphone weights is independent of the source location and microphone locations. It is also shown that, theoretically, it is possible to obtain infinite reductions at the virtual location. The analytical expressions are compared with forward difference prediction techniques. The results demonstrate that the maximum attenuation, that theoretically can be obtained at the virtual location using forward difference prediction techniques, is expected to decrease for higher excitation frequencies and larger virtual distances.

Adventures in Active Noise Control

“…This sensing method involves estimating the sound field at a location remote from the physical sensors and using an active control system to minimise the sound field at the remote location. There have been a number of excellent papers published on this topic [13][14][15][16] and more recently, the technique has been extended to using fixed microphones to generate a moving virtual microphone [17][18][19][20] . Why is a virtual microphone of interest?…”

“…Thus it is necessary for the virtual microphone to be capable of moving with the subject's ear. The location of the ear in 3-D space can be determined using ultrasound 18 , much like some cameras do when focussing automatically.…”

Near-field error sensing for active directivity control of radiated sound

“…15 Peterson et al investigated the virtual error sensing in a rigid-walled acoustic duct and found that theoretically it is possible to obtain infinite reductions at virtual locations and this can be extended to create a moving quiet zone, but the noise reduction will decrease for high excitation frequencies and larger virtual distances. 16,17 Petersen et al proposed a virtual sensing algorithm for local active noise control systems using Kalman filtering theory and demonstrated its effectiveness by implementing the algorithm on an acoustic duct arrangement. 18 A problem with the virtual error sensor arrangement is that it requires preliminary identification of the system.…”