On Fri, 10 Jun 2005, Michael Huffman wrote: > I think I am going to try out the analog idea, and see how it works on one > window. I reckon that if I mount everything properly just outside the > window, I might get enough of the effect that I want without the howling, and > then do the other two windows.
Schematic: noise-cancelling headphones http://headwize.com/projects/noise_prj.htm In fact, this is yet another "energy sucking antenna" effect. As with EM antennas, if we emit sound at the same frequency of incoming waves, and if we adjust the phase and amplitude of our emitted waves, then energy should disappear, and the device behaves as an absorber. Also, I imagine that you'd want to include a low-pass filter which only lets the system work at wavelengths much longer than the diameter of the loudspeaker. The phase shift might be 180 at long wavelengths, but the phase would be wrong at shorter ones, and so it would break into high freq oscillation even though it was still "cancelling sound" at the lower frequencies. (((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty SCIENCE HOBBYIST website billb at amasci com http://amasci.com EE/programmer/sci-exhibits amateur science, hobby projects, sci fair Seattle, WA 206-789-0775 unusual phenomena, tesla coils, weird sci
