ABSTRACT
Chapter 6 deals with active control—the most complex in terms of hardware and algorithms, and thus involving the greatest implementation cost, but giving the greatest flexibility and the possibility of achieving higher levels of sound reduction. In the case of active control, proper selection of measurement and actuation elements, as well as their mounting locations, is crucial. Their presence affects the properties of the object due to the non-zero mass, especially in the case of vibration exciters, but most importantly the ability to observe and control subsequent mods. Therefore, the first part of this chapter presents a method of optimizing the placement of measuring and actuating elements based on a formal approach known from control theory. The method of construction of the electronic system and data processing is also described. The control structures—feedforward and feedback—are presented. Attention is paid to the internal acoustic feedback. The method of control with virtual microphones is presented, which enables the reduction of estimated sound pressure based on other measurements. Control algorithms based on Least Mean Squares family are discussed. The problems of stability and effective implementation are pointed out. Many design guidelines and specific algorithmic solutions for multidimensional control systems are given.
