Abstract From:
Kenneth A. Cunefare and Steve Shepard, "The active control of point acoustic sources in a half-space," J. Acoust. Soc. Am., 93(5), pp. 2732-2739 (1993).
Analysis of active noise control applications generally neglect the presence of nearby reflective surfaces, such as a ground plane. The research presented in this paper examines the impact of the presence of a nearby reflective plane on the active control of sound radiated by a number of point sources. It is shown that when the sources to be controlled are within one wavelength of the reflective plane, be it rigid or pressure release, that the plane can significantly impact the control versus control under free field conditions with the same source separations. The orientation of the noise sources and the control sources with respect to each other and to the plane also significantly influences the control. For sources more than one wavelength away from the reflective plane, the use of the simpler free space analysis yields acceptable results as compared to using the more complex half space analysis.
Shown below is a noise source (primary) and a control source (secondary) above a pressure release or acoustically rigid plane.
An active noise control analysis was performed to minimize the total acoustic power with the sources in various configurations with respect to the plane. The impact of the plane presence of the the solution was studied by comparing the active noise control solution with that found in a free-field configuration.