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Some questions regarding sub-floor IB installation
Some questions regarding sub-floor IB installation
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Old 5th February 2010, 07:04 PM   #1
synessence is offline synessence
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Join Date: Feb 2010
Default Some questions regarding sub-floor IB installation

Our newly purchased home does not have a basement, but it does have a 4' high concrete-walled sub-floor that runs under the entire home. Inspired by Tom Nousaine's 'sub that shook the world' article from 1999 and many of the glorious attic/basement/crawlspace designs that have been shared here I've resolved to construct my own sub-floor IB assembly. I have a few questions that I think experience alone can answer. Any wisdom you can bestow would be gratefully received:

- First, on question about the theory. I'm just confused as to how a standard home floor can possibly be dense and non-porous enough to act as a baffle for low frequencies which by their nature are so penetrative. It seems to me that SOME level of wave cancellation must be occurring at the listening position, and it further strikes me that the amount of cancellation might well vary with frequency. Is it simply that the back waves are attenuated enough to make the net gain workable?

- The sub-floor area in question is about 2500 cu ft and is completely sealed save for two 8x19" openings to the outside world intended to allow for ventilation/drying of the sub-basement. I know that for sealed enclosures such a leak would be fatal, but if I'm understanding the purpose of IB designs, backwave pressure has no influence on the system so really the only risk that I'm running is annoying the neighbors, is that correct?

- I know that placing a sub in a corner makes for deeper, smoother output but I'm wondering if my circumstances trump that consideration. In my case the two workable corners in which to vent are are either a) behind the listening position or b) in a corner of a triangular part of the room that is actually 12' BEHIND where our screen and main speakers will be. In both cases, the corner positions are close to the above-mentioned venting ports to the sub-floor (which may or may not matter). Would either of these considerations cause you to move the position of your array? The other option that would utilize SOME measrure of boudary reinforcement would be to put it against the wall to the side of the monitor, which is a bout midway through the room.

- Are there specs (Thiel-Small) that I should be looking for for this kind of use? Can anyone suggest some drivers that are a good marriage of performance and price? I'm not really interested in chrome-plated baskets or any other cosmetic silliness.

- Without some sort of maths to guide me I am just guessing at what kind of cone area and power I'll need. Is there a good guide based upon room volume and desired SPL?

- It would seem that EQing is really required to do this properly - is that the case? Is an RTA required for this or there a cheaper method that is as effective? Is there a salient article or guide to do this properly?

Thank you so much for any consideration that you can spare me. If I'm going to cut a hole in my floor I only want to do it once, so having some confidence in these decisions goes a long way.
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Old 5th February 2010, 10:27 PM   #2
DougSmith is offline DougSmith  United States
diyAudio Member
Join Date: Oct 2008
You'll find a lot of information addressing your questions here:

"Cult of the Infinitely Baffled"Hear The Bass, Not The Box The definitive online resource for Infinite Baffle subwoofer designEstablished 1999 - Home
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