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Discussion Starter #1 (Edited)
Why did I build this? For the exact same reason George Mallory climbed Mt. Everest, "Because it's there." That and maybe because of all the internet know-it-alls who told me it wouldn't work.

"it's" in this case being a nice big old brick fireplace smack dab between in the middle between my two main speakers, hidden and made unusable by my new 60" flatscreen. This build couldn't be easier or cheaper. I used a single JBL 2245h, a sheet of MDF, a 16' roll of metal roof sealant and eight masonry bolts. The flue was left open.

How does it sound? Magnificent! Power is from a bridged BGW 620b, crossover is 24 dB/8ve at 40 Hz. Mains are JBL SVA 1800's. I use it occasionally for movies at fairly low levels, but I mainly I use it for music, most of which is 24 bit downloads.

The chimney is about 30 ft long, so I calculate a fundamental open pipe/closed pipe resonance of around 9 or 10 Hz. which doesn't seem to be a problem as it it's outside the range of most material. There is room for another 18 on the baffle, so if I get upgradeitis, that will be my next move. I screwed the bolts into the mortar between the bricks so it will be easy to remove when I upgrade or sell the house. In the mean time I'm getting the cleanest most satisfying glorious bass I've ever heard in my system or any other, but this is after all, the first and only IB I've ever heard. I can't imagine ever going back to conventional box bass.
 

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+1, very nicely done! The only thing I might add is...you might consider painting the bottom of the MDF black to make it blend with the surroundings. Just a thought. :T
 

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Discussion Starter #4 (Edited)
+1, very nicely done! The only thing I might add it you might consider painting the bottom of the MDF black to make it blend with the surroundings. Just a thought. :T
The had to move the cable box up to get better remote response so it's pretty stealthy back there now, but I need to get around to doing that.

I'm playing Reference Recordings Organ Polychrome 24 bit/176 right now, and it does seem to be working that solo 18 a little close to its Xmax, but boy are we going deep! The room is well damped, fully carpeted and 63 feet long in one dimension, with lots of alcoves, hallway entrances and other irregularities.
 

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I'd argue that it's technically an Transmission Line and not an IB... but that doesn't mean the idea and its execution don't bring a smile to my face. I love it. I build a partition wall IB (it's a high aspect ratio enclosure at 10x Vas of the 4 drivers, so mine also fails to meet the strictest definition of IB), andI couldn't agree with you more. I'm never boxing a subwoofer again.

I gotta ask though... how does it sound outside your house? Do you have any angry neighbors yet?
 

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Discussion Starter #7 (Edited)
I'd argue that it's technically an Transmission Line and not an IB... but that doesn't mean the idea and its execution don't bring a smile to my face. I love it. I build a partition wall IB (it's a high aspect ratio enclosure at 10x Vas of the 4 drivers, so mine also fails to meet the strictest definition of IB), andI couldn't agree with you more. I'm never boxing a subwoofer again.

I gotta ask though... how does it sound outside your house? Do you have any angry neighbors yet?
And I would argue that it behaves nothing like a real transmission line, nor like the speakers that are commonly marketed as transmission line speakers, such as vintage IMF's. A real transmission line, be it acoustic or otherwise, "fools" a wave into not reflecting at the intersection of two dissimilar transmission media, like the wedges in an anechoic chamber fool the sound into the solid wall at the fat end of the wedge. "Transmission line" speakers are really just 1/4 wave resonators that dump the resonance back into the listening room.They do absorb upper frequency information along the way, but that's incidental to their real design function, which is to augment the low end of a speaker. What I have is a 1/4 wave resonator that dumps the resonance and rearward information into the sky. So on the roof it's acting like the bottom half of a misnamed transmission line speaker, but in the room, since there is insignificant back pressure on the driver and virtually all rearward radiation is ducted away, just like in a manifold IB, it's acting like an IB. The 1/4 wave resonance, 8 or 9 Hz, is below even the lowest pipe organ notes, so that's not an issue with music, I know there might be some junk down there in Blu-ray movies, but that's not what I use this for. I've done some sweeps all the way down to 1 Hz, and nothing crazy happens at F1, but it is putting out some serious energy down there as evidenced by some structural creaking down the hall and up the stairs.

I suppose if I went up on the roof with the music playing I would hear something, but it is completely inaudible from the ground, even at very high levels in the house, so that's not an issue. It's doesn't act like the sealed trunk of a competition Civic rolling past your house or in the lane next to you at a stop light, it's a different beast entirely, acoustically speaking. There really are no downsides to this setup, except that I won't be burning any yule logs next month.
 

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I have always wanted to build a subwoofer in the space underneath my stairs. It is closed in and wasted space, someday maybe....
 

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I suppose if I went up on the roof with the music playing I would hear something, but it is completely inaudible from the ground, even at very high levels in the house, so that's not an issue. It's doesn't act like the sealed trunk of a competition Civic rolling past your house or in the lane next to you at a stop light, it's a different beast entirely, acoustically speaking. There really are no downsides to this setup, except that I won't be burning any yule logs next month.
I was wondering about this too. I know I can hear someone's bass near me on quiet nights, and I'm sure when my dual 18's get built a few of the neighbours will be able to hear them even from the basement. I thought backfiring up the chimney would have been pretty loud, but it sounds like you have the perfect solution there.
 
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