Subject: is it possible to cancel out sound thats being blasted from a speaker?

I know that there are Noise Reduction headphones on the market at the moment, but i was wondering if the technoldy exists that will cancel out(180 degree phase shift?) sound being blasted from speakers at distances of about one hundred yards or less. Is there a cost effective way of deigning a circuit which would achive this?  Or is the technolgy impossible to do at this level?

Thanks for any reply,

Adam

Re: is it possible to cancel out sound thats being blasted from a speaker?