SAE 2015 Noise and Vibration Conference and Exhibition

June 22-25, 2015

Grand Rapids, Michigan, USA

DeVos Place Convention Center

Keynote Address - Awards Luncheon

Wednesday, June 24 - 12:00 - 1:30 p.m., Ballroom A

Global Active Noise Control Using Acoustic Energy-Based Techniques

Scott D. Sommerfeldt Scott D. Sommerfeldt
Dept. of Physics & Astronomy
Brigham Young University

There has been an interest in active noise control for the past thirty years. One challenge that has existed is that active control approaches that have typically been used often result in localized control of the sound field. Thus, one might achieve very high attenuation at the location(s) of error sensors, but may have little or no attenuation at other locations. There are a number of applications where global control, or at least attenuation over an extended region, is desired. Two general concepts have been investigated by researchers in an attempt to extend the region of control. One concept is that of decentralized control, in which multiple independent control systems can be implemented in a decentralized fashion such that the overall region of control is increased. The second concept is to develop a control system that yields an extended region of control (ideally global) in its implementation. This address will focus on this second concept and in particular, will overview some active control techniques we have developed that are based on minimizing acoustic energy quantities, including sound power and energy density. These acoustic energy quantities are directly related to the overall acoustic response in the field, so if one can successfully attenuate these energy quantities, the result is global attenuation of the field. It has also been found that using this approach results in active control solutions that are significantly less dependent on the location(s) of error sensors.

Several applications will be reviewed where we have been able to develop active control systems that yield global, or nearly global, attenuation of the field. The first application targets enclosed sound fields at low modal density and specifically focuses on attenuating the sound field in the cab of earth-moving equipment. Research has found that minimizing acoustic energy density can often achieve greater global attenuation in low modal density fields. Thus, this approach has been applied in the cabs of earth-moving equipment, and the desired objective of global control has been largely realized. Another application targets free-field radiation, and specifically focuses on sound radiation from small axial fans. To achieve global attenuation requires that the total radiated power be minimized. However, this represents a quantity that is difficult to measure and incorporate into a control system in real time. A method has been developed that uses the concept of minimizing radiated power, but which is implemented using microphone error sensors placed in the direct near field of the fan, leading to a very practical configuration. Additionally, we have been developing a method that is effective for attenuating the sound radiated from vibrating structures, such as a panel. This technique uses vibration sensors, but is configured to approximate the attenuation of radiated sound power. These energy-based techniques will be overviewed, and results will be presented indicating the control that can be achieved and the global characteristics of the resulting sound field.