See the SoundBlox product at
http://theproudfootcompany.com/soundblox-information.html
They modify ordinary hollow cement masonry blocks by cutting a slot into the
hollow cavities where an absorber, as well as the porosity of the
cement-cinder mix, absorb over a specified frequency range.
Angelo Campanella
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I do not know what you mean by "interference".
Could it be this:
http://en.wikipedia.org/wiki/Active_noise_control
(the Wiki article is rather poor)
w.