<title>Feedforward active interior noise control</title>

Abstract

Analytical and experimental studies undertaken for controlling noise in the interior of a three-dimensional enclosure with a flexible boundary are presented. The rigid boundaries are constructed from acrylic material, and the flexible boundary is constructed from aluminum material. Noise generated by an external speaker is transmitted into the enclosure through the flexible boundary and active control is realized by using Lead Zirconate Titanate (PZT) piezoelectric actuators bonded to the flexible boundary. Condenser microphones are used for noise measurements. For panel and cavity controlled modes, analog controllers based on feedforward schemes using acoustic error signals are developed and discussed.

Studies on performance functions for interior noise control

“…In this paper, extending on the work previously reported by us [2,[20][21][22], analytical and numerical investigations into performance functions for interior noise control are presented. The primary contributions of this work are the following: (a) formulation and comparison of zones of quiet for different performance functions for control of sound fields enclosed in three-dimensional enclosures; (b) investigations into the influence of the locations of actuators on sound pressure levels inside the enclosure; and (c) investigations into the control mechanisms associated with different performance functions in three-dimensional enclosures for panel and enclosure modes.…”

“…Here, noise control in the interior of a helicopter is of interest. The primary contributors to noise spectra in helicopter are the main rotor, tail rotor, and turbines in the frequency range of 50-500 Hz and gear mechanisms in the main transmission for frequencies above 500 Hz [1][2][3][4][5]. The sound and vibration energy is propagated through the structure (structure borne radiation) or through the air directly (direct radiation) to excite the cabin walls.…”

“…An example of a study using secondary acoustic sources is the study of Bullmore et al [7]. Examples of studies using secondary force inputs include references [2,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] where the force inputs have been realized by using either electrodynamic shakers or piezoceramic actuators. The nature of an enclosed sound field may be characterized by the Schroeder frequency (e.g.…”

Active feedback control of multiple waves in helicopter gearbox support struts

“…The transient and persistent disturbances generated by the gearbox mechanisms as well as the main rotor are transmitted through the struts into the fuselage; this transmission is one of the main sources of structure-borne noise in a helicopter cabin. The frequency components associated with this noise lie in the bandwidth extending up to 6 kHz [3,4].…”

“…Among many approaches pursued to realize cabin noise reduction, control of waves transmitted through the noise path such as struts has been found to be viable. An early initiative 3 Corresponding author. in this regard is due to Westland Helicopters Ltd. During the late 1980s, they demonstrated that considerable reduction of the average vibration level can be achieved by using an active control of structural response (ACSR) system at the blade passing frequency of 17.5 Hz [1,5].…”