This is my first post on the AVS forum, so thanks for having me. I'm currently doing a master's research thesis on using a speaker array to control room acoustics via the use of out-of-phase cancellation. My question is relatively vague, but it obviously requires alot of background info first so...
I've worked with everything from a 2 speaker array to a 12 speaker array and many different sizes inbetween. Essentially, I'm pumping a low frequency sine wave (I've used 200, 320, 500, 800 and 1kHz sine tones) through a single source speaker towards the audience section in a shoebox sized room (aprox 18 meters long, 7 meters wide, 5 meters tall). My array then is placed inbetween the the source and the audience (pointed towards the audience) in a way to account for time delays etc. All speakers have been calibrated accurately for volume and time delay based on distance from the source so that the sine wave output by each speaker in the array is exactly 180 degrees out of phase with the wave coming from the source once it passes over it.
What I get are patches of extreme cancellation (source outputting 100db and areas of cancellation of less than 40 db) randomly around the room. Each frequency yields different areas of the same extreme amount of cancellation, but most areas are spherical with a diameter of around 40cm. There seems to be no rhyme or reason to the location and size of these cancellation areas.
Now the room is not anechoic so I know there are plenty of reflections reducing the effeciency of my system; however, shouldn't I start to see some regularity in the wavefront output by the array? I've put as much insulation (duvet covers) all over the walls to try to dampen the room as much as possible. I know they're not the best insulation, but that's why I'm not using any tones below 200hz. Without getting into too much detail, I can assure you that the distances between each array speaker and each other are well under the wavelengths of the test tones and their volumes are calibrated in accordance with the decay per distance metered by the source playing by itself.
I'm hoping to see a larger area of cancellation maybe 1-2 meters directly in front of the array, but so far I have only seen random circles of cancellation all over the room. Has anyone else dealt with array cancellation much? I of course have a thesis advisor here who helps out as well, but I just wanted to throw this out there for second opinions. Any help in achieving more widespread (location-wise) cancellation would be of great help. Thanks a bunch everyone!