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Sub In The Fireplace

Was wondering what your thoughts are on this. I currently have a Velodyne HGS 18 II, which I have tucked in my fireplace... The mains sit on either side, with their plane about 2 feet closer to the listener. The fireplace, which I obviously don't use, is pretty much in the middle of the wall. The sub fits easily with approximately 2 - 6 inches of breathing room on any given side. Being in a fireplace, the sub is surrounded by brick on 5 of its 6 sides. The house is on a slab. Is this a good thing? Am I losing anything having it there? Advantages, disadvantages? Should I consider insulating the breathing room the sub has all around it?
vectorman67
flex
292 posts
 
Sogood,
I measured my room response before, during and after treating the fireplace. Placing absorbers or diffusors inside the fireplace cavity, or covering the front with glass doors and partially treating the exterior did not work either. 8' tube traps do work.

Vectorman, if you haven't found the problem so far, then you probably don't need to worry about it.
flex
292 posts
 
By the way, I should mention that my main speakers at the time were rear-ported, which probably exacerbated the energy distribution into the fireplace behind the speakers. But Vectorman didn't mention what his main speakers are, and IME the speaker radiation pattern affects some room acoustic problems.
zaikesman
3,017 posts
 
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... ;^)
rives
953 posts
 
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.
vectorman67 OP
42 posts
 
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?
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