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Discussion Starter #1 (Edited)
I have a cement shelf that wraps my theater room. My dimensions are 16ft x 22ft x 10ft. The cement shelf 46" high and 18" deep. If I place a drop ceiling they will be 8ft. So from the shelf to the ceiling is approx. 4ft. If I build a baffle wall for my front speakers I can add another 18" from the cement wall. Im curious if I have the space to build an I.B. either behind my front baffle wall OR down the side walls. (keeping in mind if I use the side walls the speakers will be 46" or higher with a 18" depth). I could build a false wall on the right side against the concrete and use that space for an I.B.
My other option would be to use the side wall that leads into the basement using that open space for an I.B.
Its still a build in progress so now is the time to make the changes.
 

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Discussion Starter #4
The drivers could be 12,15,18 no preference. The problem I am having is with the space itself. When I build the front baffle wall. I will have an closed area 16ft wide but only 18" deep up to the 46" cement shelf. Then it will open to 3 feet from the baffle wall to the back wall extending the additional 4 feet to the ceiling. If I build a false wall along the right side it would 18" deep X 48" high X 22 feet long. In not sure an I.B. will actually work since the space is so shallow. It's long but shallow. I was consider a line array type behind the front baffle wall. As far as the side wall, maybe 2 subs facing each other with a hole in the wall to port the sound.
Is my only concern the "volume" regardless of the shape and depth of the walls?
 

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I am definitely no expert when it comes to IB, my understanding is that you want the largest area behind the driver you can manage so that it doesn't act like a box.
Having said that, the area you have available should be adequate to get some decent results and I don't think the depth is an issue as long as the driver is not near any side walls so that the sound pressure can spread evenly behind the driver.

If I'm wrong I hope someone else will pick me up on it. :)
 

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It's all about the speaker you choose, you will need a minimum of 4 times the VAS rating of the speaker (for volume). But optimally 10. So find out which IB speaker you are interested in and use those specs to see if you have enough volume.
 

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Looks like you have a similar problem to mine... I wanted IB, and had to build a partition wall to enclose the back side. The total internal volume behind my wall is about 136 ft^3, so I followed the Vas *10 rule and selected drivers whose Vas was 1/40 that volume. (Using four drivers, 136 / 10 / 4 = 3.6) Fortunately for me, the drivers that most closely matched the specs I was after also happened to be a decent quality low-budget driver from PE. I'm still doing construction on this monster, so I'm a ways off from getting things all dialed in. Initial tests have gone extremely well though.

The bottom line is that even with fairly limited rear enclosure volume at your disposal, an IB setup is definitely not out of reach. Something to watch out for though: If you go the line-array route for the drivers, be prepared to brace the wall very heavily. All that mass moving in unison generates a lot of vibration in the structure to which it's mounted.
 

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It's all about the speaker you choose, you will need a minimum of 4 times the VAS rating of the speaker (for volume). But optimally 10. So find out which IB speaker you are interested in and use those specs to see if you have enough volume.
Right; now WRT the shape of the I.B., if it has a high aspect ratio such 1.5 x 4 x 22 ft, then instead of the ~uniform particle density that a speaker program assumes, it's a 1/2 WL resonator, so room modes will dominate its frequency response, making driver positioning critical for best overall performance, i.e. needs to be at an odd harmonic of the longest dimension in two planes of both this short wall 'sub' and the room wall height, width, so finding a solution will set the shelf height.

I learned this the hard way with a 300 ft^3 false wall IB loaded with a stereo pair of dual 15" 'subs' XO'd at 120 Hz. With no way to EQ it beyond the bass tone control on the amp, it was horrible since I'd positioned them to just look good. Even if I'd had today's digital EQ, I still couldn't have done anything about the huge dips except by shelving the rest, which was a no-no due to the low power available meant keeping efficiency high, especially since I was mating them to SET driven theater horns.

Bottom line, doing this right requires the fewest drivers, but this often causes too many compromises in the system design unless the woofers are placed in the corners [horizontal and/or vertical], so most folks resort to making a 'wall of sound' with lots of inexpensive drivers and relatively little power, then EQ it.

GM

Almost forgot: http://ibsubwoofers.proboards.com/
 
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