ABSTRACT
Since active noise control became a practical reality, commercial installations have suffered from insufficient sound source robustness. The robustness requirements necessary to ensure the survival of the sound source obviously differ from one installation to another and clearly active control sources in air conditioning ducts will have different requirements to those in an industrial air handling system in which the environment is very hostile. The sources needed to generate the antinoise must be capable of producing noise levels similar to those produced by the unwanted noise source. Typical acoustic sources include loudspeakers and horn drivers. Vibration sources are used sometimes to control the vibration of surfaces that are radiating the unwanted sound. Typical vibration actuators are piezoelectric patches, piezoelectric stacks, magnetostrictive actuators, electrodynamic shakers, inertial shakers, electromagnetic actuators, hydraulic and pneumatic shakers.
