ACTIVE CONTROL OF EXTENDED ACOUSTIC SOURCES IN A HALF-SPACE

Many noise sources, such as an electronic transformer, are located on or near an acoustically rigid planar surface, such as a concrete floor . Thus far, however, most of the active noise control research has bee n based on the free-field assumption. The work presented here investig ates the effect the presence of a rigid plane has on the active noise control of an acoustic source with characteristic dimensions comparabl e to the acoustic wavelength at the frequency of interest. It is shown that when the source is located a distance of one wavelength or more from the plane, the presence of the plane may be neglected. However, t he minimum radiated power computed using a free space active analysis can be significantly greater than that predicted using a half space ac tive analysis for distances less than one wavelength. As a result, usi ng the simpler free space analysis techniques leads to less effective control for distances less than one wavelength.