IB. Need advice please.

[Rolyasm]

My friend is building a dedicated HT next to his attic. I thought it might be a very good possiblity to build him him an IB. Below are the pics and dimensions. The HT is surrounded on two sides by the attic. One side is a lot larger, but both are connected. It wouldn't make a difference which side the IB went, the smaller or larger, as long as they are connected? I drew my idea on the picture and labeled the IB sites #1 and #2. Those positions would make it easier for running wire and setup. He wants a nice sub but doesn't want outrageous cost. So if we could stay under the $1,500 range, that would be a lot nicer. $1,000 would be better. Dimensions are 29 x 15 x 9, but the rafters slope at a 31 degree angle. The connecting side is 14 x 6 x 9, with a very steep slope on the roof. The two sides form and "L" shape. So ideas on drivers, rough costs and amp power needed would be appreciated. Thanks a lot and I promise not to ask as many questions on this go around and it won't take a year to build either. :T
Roly

[Rolyasm]

I think I figured this correct. The one side I have as 6 x 14 x 9=756 cf. The other side is 29 x 15 x 9=3915 cf. Add those together to get 4671 cubic feet, then I just estimated a 1/2 reduction d/t the rafters. So around 2335 cubic feet or 66,094 liters. If I figured this correct, I could use a lot of drivers with high Vas and still be ok. So any suggestions on some 15" or 12" drivers? I read the thread about the Canadian drivers and they sound interesting. I looked at Ascendant but I really don't know what to look for as to what would work best in this situation.
Roly
P.S. Thomas, I bought another book on audio and electronics. Trying to make you proud of me.

[ThomasW]

Sorry but the pictures are basically unintelligible.

For a room that size use 4 Soundsplinter RL-p15" D4, powered by a Behringer EP2500 and get a BFD to handle the EQ.

Obviously one needs to check room placement in advance of purchasing components. Use the methods described on the IB FAQ page.

[Rolyasm]

Thanks Thomas. I am really excited for my friend. More so than he is because I don't think he understands what he will have when we finish. I think we will have to do a cube-type or rectangle manifold on the side of his mains. Sounds like it isn't an issue but I will check placement. Anyway, read the FAQ's, just a few questions. I understand that the larger opening into the room is better, however I see a lot that are about the same size as the drivers. Is the rectangular box an inherantly better design over the cube because of the larger opening into the room? Or, say I could build a pyramide shape, so my drivers are closer to the tip of the pyramide. I understand this would be difficult, just trying to understand the principle. In theory this pyramide design with a much larger opening should sound better, correct?
Last question. Are there any drivers you would recommend that are one-step under these Soundsplinters but close in performance. Just so he can have an option.
Thanks
Rolyasm

[ThomasW]

Most of your questions are answered here

http://home.comcast.net/~infinitelybaffled/page2IB-IBmanifold.html

There is no benefit to a pyramid. There's a disadvantage in that it doesn't provide for mechanical cancelation like a straight side box with the drivers mounted in opposition.

There are no step down drivers. There are Mark's from Canada, the various offerings from PE, there's Soundsplinter, next are the more expensive one's from TC-Sounds.

One thing to note is that one RL-p15" costs about the same as 2 PE drivers and will play as loud. He could buy 2 RL-p15" and see if that's loud enough. If it's not he could add 2 more to the same manifold. If he buys 4 lower output drivers he's toast because there's no room in the manifold to upgrade.

For months people have been talking about bring new drivers to the market, but so far none have appeared.

[Rolyasm]

Thanks,
I looked at the FAQ's again and didn't see whether or not a rectangular design would be better than a cubed design. The rectangular design would seem to give you a larger opening and perhaps a better response. The only down side I can see is that if we do the rectangular and only use two drivers, one half of the rectangle would be void of any drivers. Is this an issue? I really think this is the last question. The IB site is really informative.
Thanks
Roly

[soho54]

The only down side I can see is that if we do the rectangular and only use two drivers, one half of the rectangle would be void of any drivers. Is this an issue?

I wouldn't worry about that too much. There are several people who have done this in the past, with no apparent ill effects. If you are still worried, fill the extra area with insulation, until you get the remaining 2 drivers. Problem solved.

[WillyD]

AE, whenever they open up shop again, has a good deal on drivers.

http://www.aespeakers.com/

4 for $400 (for their IB model, which I presume will be a pretty solid performer) is nice.

[ThomasW]

The FAQ says...

The fundamental rules for manifolds are 1) make the outlet as large as possible, and 2) keep the manifold as short as possible.

The decision as to the shape of the box is basically determined by the available space. Generally speaking the larger the box and the larger the opening, the better the sound quality. There is no sound quality difference between a rectangular box and a cube if they are the same size. So choose the shape that fits your needs.

If one uses a rectangle and 2 drivers, it makes sense to block off the part of the manifold not used.

Willy,
IF AE reopens, and IF AE starts reliably shipping drivers in a timely manner, the products will be considered.

[Rolyasm]

Alright. Got it. I appreciate all the help. I will try to take some photos and keep you updated if I have problems. He is about to sheetrock, so it may be awhile before we get it all setup and tuned. Thanks for all the help. If some similar but cheaper drivers come on the market in the next few weeks, please let me know. I will browse the forum to keep my eye open. Thanks a lot. Shouldn't be hearing from me for awhile.
Roly

[WillyD]

Willy,
IF AE reopens, and IF AE starts reliably shipping drivers in a timely manner, the products will be considered.

Of course.