I have got a seating position on a riser with plywood on 2x6's in the back "row" of my HT. This rests on my concrete basement floor. I notice that during low frequencey sounds that the floor vibrates some. I like the effect and am considering getting a second sub that I would modify to fire down to enhance to effect on the floor. My question is: Could I get by with a cheap one if I turned the crossover way down so that it would only produce the rumbles and not alot of audible sound? I don't want to pollute the soundfield with a tubby cheap sub, but would like some additional physical rumbles. I realize there are other products that do this but this seems like it wouldn't be alot of trouble to do. Opinions...?