A generalized approach to modal filtering for active noise control. II. Acoustic sensing

Abstract

Scaling laboratory-sized active noise control systems into industrial-sized implementations is a difficult exercise. Problems relating to sensing system design account for some of the difficulty. In the first part of this paper, an alternative approach to sensing system design was presented where acoustic radiation patterns are decomposed using fundamental acoustic quantities, rather than structural modal based quantities. In this paper, the approach is tackled in the acoustic domain instead of structual vibration. The technique has been simulated in the time and frequency domains using acoustic sensors and implemented experimentally.

Local sensing/control or global error sensing/control in structural acoustics: A comparison of two techniques influence over sound power

“…The foundation of the approach is sensing orthogonal multipole radiation patterns [11,44]. The technique is amendable to both structural and acoustic sensing [8,[47][48][49][50]. The multipole decomposition technique begins by writing the acoustic pressure radiation from a (any) source in terms of acoustic multipole radiation patterns, similar to decomposition of structural velocity distribution in terms of in vacuo mode shape functions [11].…”

“…In this case the radiation transfer matrix is independent of any structure properties and is dependent on the transfer function of the most fundamental acoustic radiator, the monopole, and the properties of the fluid surrounding the noise source. The weighting matrix A multi was shown not to be diagonal [11,47,48], however it is symmetric, and so can be diagonalised using an orthonormal transformation. A control system based on this decomposition method would then attempt to measure the amplitude of the acoustic multipoles, a, that comprise the total sound field.…”

Operational modal filter and its applications

“…In recent years, several teams of researchers have developed the use of modal filters and have applied the results of such analyses in the tasks of vibration control, damage detection, and load identification [1][2][3][4][5][6][7][8][9][10][11][12][13]. Generally speaking, the modal filter extracts the modal coordinates of each individual mode from a system's output.…”

Practical implementation of an acoustic-based modal filtering sensing technique for active noise control

“…In this paper the multipole approach [37][38][39] to sensing system design, where radiated power can be decomposed into an orthogonal set of radiating multipoles is experimentally examined in detail. The multipoles are a set of functions made up of in-and out-of-phase monopoles used in the modelling process.…”