Sub In The Fireplace

This is the best thread title I've seen in a long time! My suggestion would be to stuff the chimney with fiberfill and turn it into a giant transmission line by opening the flue... ;^)

The leveling jacks are to hold the plywood and Owens corning fiber board over the flue and while it is pressing up on this--it will also be pushing the sub down--just creating a very rigid positioning of the sub. It is very important to wall off the flue. Flex has shown the problems he had, but my guess is his fireplace was bigger and didn't adhere to the 1/4 wavelength rule for his cross-over point. This would most probably yeild a major bump at probably 2 low frequencies and a very colored disappation of energy. If you looked at a waterfall plot of a sub enclosed in this manner you would likely find at least one and perhaps 2 prominent frequencies that held energy for a long time. Again--this is why it's always good to take an acoustic measurement--then you can be sure. This is a theoretical model--and I have not tried nor measured the response in a fireplace (but now a really want to and compare those greater than the 1/4 wavelength rule and those less than the 1/4 wavelength rule). If you do measure it I would be very interested in your results.

Hi Flex, sorry I neglected to mention my speakers. My mains are an older pair of full range B&W DM3000. They are not ported. The sub, as I had mentioned, is a Velodyne HGS18 II, which is also not ported.

Rives,
I like your idea of creative a very rigid positioning of the sub. I'm a bit unfamiliar with the wavelength rules your citing... e.g. 1/4 wavelength, 4.7' for 60 Hz, etc... would you mind explaining?

Sound travels at 1130 feet per sec. Thus (1130/60)= 1 wavelength for 60 Hz 1/4 of this. The reason I choose 1/4 wavelength is that it is impossible to have 2 peaked values.