Active noise control at a moving location using virtual sensing

Local active noise control systems aim to produce zones of quiet at a number of desired locations within a sound field, such as the ears of an observer. The resulting zones of quiet are usually centered at the error sensors, and are often too small to extend from the error sensors to the observer's ears. To overcome these problems, virtual sensing methods have been suggested. These methods are based on estimating the error signals at a number of locations remote from the physical locations of the error sensors. By minimising the estimated error signals, the zones of quiet can be moved away from the error sensors to the locations where noise control is desired, i.e. the virtual locations. In this paper, the active noise control problem under consideration is analysed using a state-space model of the plant. Kalman filtering theory is then used to develop a virtual sensing algorithm that computes optimal estimates of the error signals at the virtual locations. The developed algorithm is implemented on an acoustic duct arrangement, and the real-time estimation performance at a virtual location inside the acoustic duct is analysed. Furthermore, the developed algorithm is combined with the filtered-x LMS, and the results of real-time broadband feedforward control experiments at the virtual location are presented.

… on Sound and …, 2007

Local active noise control systems can be used to generate a zone of quiet at a physical error sensor using one or more secondary sources to cancel the acoustic pressure and its spatial derivatives at the sensor location. The resulting zone of quiet is generally limited in size and as such, placement of the physical error sensor at the location of desired attenuation is required, which is often inconvenient. Virtual acoustic sensors overcome this by projecting the zone of quiet away from the physical error sensor to a remote location. The work described here investigates the effectiveness of using virtual microphones and virtual acoustic energy density sensors in a diffuse sound field. Expressions for the performance of the virtual microphones and virtual acoustic energy density sensors have been developed using the forward-difference extrapolation technique which has been rederived for use in diffuse sound fields. Results from simulations will be presented, together with experimental results obtained in a reverberant chamber.

2006

A local active noise control system aims to create a zone of quiet at a desired location, such as an observer’s ear. The resulting zone of quiet is generally centred at the error sensor, and is often too small to extend to the observer’s ear. To overcome this problem, virtual sensing methods have been suggested, which allow the zone of quiet to be moved away from the physical error sensor to the desired location of maximum attenuation, i.e. the virtual location. These methods are based on estimating and minimising the error signal at the virtual location. The control performance thus depends on the estimation accuracy of the virtual sensing algorithm. In this paper, limits on the broadband control performance that theoretically can be achieved at the virtual location are derived for a virtual sensing algorithm called the remote microphone technique. These limits are compared to the broadband control performance that can be achieved for the case of using a physical error sensor at th...

Traditional local active noise control systems minimise the measured acoustic sound pressure to generate a zone of quiet at a physical error sensor. The resulting zone of quiet is generally limited in size and as such, placement of a physical error sensor at the location of desired attenuation is required, which is often inconvenient. Virtual acoustic sensors can be used to project the zone of quiet away from a physical error sensor to a remote location. A number of virtual sensing algorithms have been developed in the past and these have shown potential to improve the performance of local active noise control systems. However, it is likely that the desired location of maximum attenuation is not spatially fixed. In this paper, a stochastically optimal virtual microphone capable of tracking a desired virtual location in a modally dense three-dimensional sound field is developed using the Stochastically Optimal Tonal Diffuse Field (SOTDF) moving virtual sensing method. The performance of an active noise control system in generating a zone of quiet at the ear of a rotating artificial head with the SOTDF moving virtual sensing method has been experimentally investigated and experimental results are presented here.

Journal of System Design and Dynamics, 2008

Active noise control (ANC) in a three-dimensional sound field (e.g., in an office) is investigated in this paper. Since the size of the controlled area generally depends on the wavelength of the target noise, it is difficult to control the noise in a whole room using ANC. Instead, noise control in the vicinity of a subject's head (referred to as around-head control) is investigated in this paper. To realize around-head control, an evaluation point that mimics head movement is required. However, movement of the evaluation point during controlling has not been considered in conventional ANC. A new algorithm is proposed in this paper to address this issue. The algorithm calculates filters as a function of position by using a time-delay filter and a distance-attenuation coefficient, which are calculated from the position of the evaluation point. Computer simulations of acoustic characteristics in an anechoic chamber and an ordinary office are conducted. The results of these simulations demonstrate the effectiveness of the proposed algorithm.

2006

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.

The Journal of the …, 2005

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 can not always be located close to an observer's ears. Virtual sensing is a method which 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 rigidwalled acoustic duct with arbitrary termination conditions. The expressions are derived for tonal excitations, and are obtained by employing a travelling 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, which 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.