Identification and control of acoustic radiation modes

A formulation is given of reduced-order acoustic radiation sensors and\ud reduced-order actuators for broadband sound fields. Methods are presented\ud to determine these descriptions from measured data, and their\ud application in systems for broadband active noise control is discussed.\ud One application area is the reduction of sound radiated from plates with\ud structural actuators and structural sensors, using measured or modeled\ud versions of the most efficiently radiating patterns of a vibrating body,\ud the so-called radiation modes. The second application of the radiation\ud mode theory is in active noise barriers for the reduction of traffic noise.\ud Without special precautions most of these systems suffer from spillover;\ud a technique is given to arrive at good reductions at the error sensors with\ud reduced spillover

Panel Resonance Control and Cavity Control in Double-Panel Structures for Active Noise Reduction

An analytical and experimental investigation of panel resonance control and cavity control in a double-panel structure is presented in this paper. The double-panel structure, which consists of two panels with air in the gap, is widely adopted in many applications such as aerospace due to its low weight and effective transmission-loss at high frequencies. However, the resonance of the cavity and the poor transmission-loss at low frequencies limit its noise control performance. In this paper, the resonance of the cavity and the panels are considered simultaneously to increase the noise transmission-loss. A structural-acoustic coupled model is developed to investigate the vibration of the two panels, the acoustic resonance in the air cavity, and the control performance. The control design can be optimized through the model using a combined stability analysis incorporating both structural and acoustic control. Finally, the results will be presented and discussed

Comparison of various decentralised structural and cavity feedback control strategies for transmitted noise reduction through a double panel structure

This paper compares various decentralised control strategies, including structural and acoustic actuator-sensor configuration designs, to reduce noise transmission through a double panel structure. The comparison is based on identical control stability indexes. The double panel structure consists of two panels with air in between and offers the advantages of low sound transmission at high frequencies, low heat transmission, and low weight. The double panel structure is widely used, such as in the aerospace and automotive industries. Nevertheless, the resonance of the cavity and the poor sound transmission loss at low frequencies limit the double panel's noise control performance. Applying active structural acoustic control to the panels or active noise control to the cavity has been discussed in many papers. In this paper, the resonances of the panels and the cavity are considered simultaneously to further reduce the transmitted noise through an existing double panel structure. A structural-acoustic coupled model is developed to investigate and compare various structural control and cavity control methods. Numerical analysis and real-time control results show that structural control should be applied to both panels. Three types of cavity control sources are presented and compared. The results indicate that the largest noise reduction is obtained with cavity control by loudspeakers modified to operate as incident pressure sources

Simulation-based design of a steerable acoustic warning device to increase (H)EV detectability while reducing urban noise pollution

This paper describes the simulation-based design methodology used in the eVADER project for the development of targeted acoustic warning devices for increased detectability of Hybrid and Electric Vehicles (HEVs) while, at the same time, reducing urban noise pollution compared to conventional acoustic pedestrian warning systems. A key component of this system is an external warning signal generator capable of projecting the warning signals to a contained area in front of the vehicle where potential at-risk situations are detected. Using acoustic beam forming principles a suitable warning strategy and an initial layout for realizing such a system is defined. Starting from this information, acoustic Finite and Boundary Element models of the transducer array allow assessing more realistically the performance impact of the system integration and of the most critical changes in the acoustic environment in which the signal generator needs to operate

Real-time Kalman filter implementation for active feedforward control of time-varying broadband noise and vibrations

Tracking behavior and the rate of convergence are critical properties in active noise control applications with time-varying disturbance spectra. As compared to the standard filtered-reference Least Mean Square (LMS) algorithm, improved convergence can be obtained with schemes based on preconditioning, affine projections, Recursive Least Squares (RLS), and other methods. The RLS method potentially leads to very fast convergence but straightforward implementations may suffer from round-off errors and suboptimal tracking behavior. In this paper a Kalman filter approach is used which, as compared to RLS, includes a covariance weighting for model output errors in order to improve tracking behavior and robustness. An orthogonal transformation scheme was used to reduce the influence for round-off errors of the Kalman recursions. In this paper an extension is given for multiple input multiple output systems, and results of a real-time implementation are presented. Conclusions are given regarding the suitability for real-time implementation of previous formulations. Different parameterizations of the secondary path model between the active control source and the error sensor are compared. Real-time results demonstrate the rapid convergence for reduction of noise in a duct, as well as numerical stability during extended operation intervals.status: publishe

Optimization of the reconstruction and anti-aliasing filter in a Wiener filter system

This paper discusses the influence of the reconstruction and anti-aliasing filters on the performance of a digital implementation of a Wiener filter for active noise control. The overall impact will be studied in combination with a multi-rate system approach. A reconstruction and anti-aliasing filter will be selected and its parameters will be varied to optimize the system level performance of the Wiener filter for a feedback controller based on an internal model control principle. It will be shown that the selection of the reconstruction and anti-aliasing filter is an important decision that can largely influence the overall system performance. This method can be used in combination with standard optimization algorithms to automatically find the optimal filters that will give the largest reduction for the overall system

Application of virtual sensors in three-dimensional broadband active noise control and the effects on the quiet zones

This paper presents various experimental results of a real-time, multiple-channel, broadband Active Noise Control (ANC) system, employing the Remote Microphone Technique (RMT) as virtual sensing algorithm in different settings. The effects of virtual sensing on the shape and size of the quiet zone are experimentally investigated. To enhance the quiet zone, an acoustic energy density probe can be used as error sensor. Such a sensor not only measures sound pressure, but also the particle velocity in three directions, providing four signals to be minimized by the ANC system. The RMT is used to construct a virtual three dimensional, acoustic energy density probe, which is validated in real-time ANC. In conclusion, advantages, drawbacks and practical considerations of using RMT virtual sensing in active noise control are discussed

Modeling and Compensation of Nonlinear Distortion in Horn Loudspeakers

Horn loaded compression drivers are widely used in the area where high sound pressure levels together with good directivity characteristics are needed. Major disadvantage of this kind of drivers is the considerable amount of nonlinear distortion. Due to the quite high air pressures in the driver the air is driven into its nonlinear range. This paper describes a technique to reduce the distortion caused by this phenomenon. Using a Digital Signal Processor (DSP), a feedforward compensation technique, based on an equivalent lumped parameter circuit, is implemented and tested in real–time in series with the loudspeaker. Measurement and simulation results are given. The overall conclusion is that a distortion reduction is obtained in the frequency span from 600 to 1050 Hz