Active control of sound and vibration

In many industrial and defense applications noise and vibration are important problems. The conventional method of treatment is to use passive damping techniques or to redesign the system. However, passive damping techniques are primarily effective at higher frequencies, and redesign is often costly and ineffective. In the last decade, active control of sound and vibration (at audio frequencies) has emerged as a viable technology to bridge this low-frequency technology gap. Recent developments have been propelled by the rapid technology growth in affordable and practical digital signal processing chips and, to a smaller degree, improvements in control transducers. In this article the authors overview the active sound and vibration control field, first by putting it into a historical context, then by outlining the relevant control theory and implementations, and finally by describing some current practical applications.