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Having looked through numerous threads and awesome DIY builds, I'm ready to start my own build. Problem is I don't have the basic skills of trying to design something. Before buying a bunch of wood and wasting it, thought I'd get some help from the experts.

Bottom line is I'm trying to build something closely resembling this: http://www.avsforum.com/forum/155-d...nt-center.html#/forumsite/3207/topics/1685882
I'd also like to get down to the 15-16Hz range to get the full listening experience.

Can someone help me design this so I have some sort of a blueprint to go off of?

Here are a few of my limitations:

Budget: $1000 +/-, but less would be better
Room size: 20' x 20' with 10' ceiling, no side walls (to left of sitting position is sliding glass door to backyard, to the right is open to the front door).
Front wall is 109" across, but I have 2 floorstanding speakers that will eat up 26", so useable sub box space is 83" wide
Sub box depth should be no more than 22-24" give or take so as not to extend too far into the room
Sub box height is not a limiting factor, but I am going to place my center speaker, cable box, DVD player, and receiver on a shelf on top so probably not more than 3' tall, give or take. Plus my TV is will be sitting on top of the cabinet as well.

Some specific questions I have:
1. Should I enclose the sub in the cabinet or do I need it to be exposed on a side somewhere? It would be nice to have it hidden for aesthetics, but what is best for functionality?
2. Should I consider dual opposed subs? I read somewhere that might reduce vibrations since I will have all my equipment sitting on this beast.
3. Should I build sealed or ported? This setup is mostly going to be used for TV/movies, and it would be nice to feel the couch shake a little. I'm afraid if I went ported my limited knowledge of how to get it done properly would result in a bad sounding system.

I have been considering the following equipment:
1. Sub drivers: SI HT18 or Dayton Ultimax 18. I'm leaning toward the SI based on price alone, if the ultimax are that much better than I would spend the extra $100
2. Amp: Inuke1000DSP for 1 sub, or the Inuke3000DSP for duals
3. Sub material: 3/4" MDF with possible veneer or I'll shop around locally to find some quality Baltic Birch 3/4".

Thanks in advance to any and all who have read this far.
 

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From an acoustic point of view, the sub cones could face the back wall, as long as there was a few inches of breathing room. This is probably what I'd do. This is somewhat like what is called "slot loading" so there might be some peaks at frequencies that should however be well above the crossover point.

Opposed subs wired in opposite phase can indeed reduce some "rocking" vibrations due to balanced forces (but that is harder. Vibration from the cabinet walls will depend how gonzo you build them-concrete? Heh, a friend did just that. If that's too crazy, there is special plywood with a damping layer. Or you can just build thick and put damping inside. For something this huge, you should step up to 1" plywood, not 3/4"…and allow for liberal internal bracing, and stuffing, and damping of the walls. Allowing for 1" plywood your cabinet could internally be 80x20x30 inches which is 28 cubic feet! That is HUGE. Yes, it would be tricky to port that properly. I'd tend to suggest sealed, stuffed, fed by a giant PA-type amplifier, and a receiver or processor with room correction.

You might also consider like 4 or 6 cheaper sub drivers, like 6 15s in a staggered zig zag so their width fits into the 80" cabinet. Mmm, or 8 15s: 4 sets of vertical pairs. With so much cabinet volume, you don't need low Q, big magnet subs. With so much cone area, they don't have to be the greatest long excursion designs. You might be able to score some great surplus buy.
http://www.parts-express.com/cat/woofers-subwoofers-midrange-speakers/31
and select 15" and sort by price. Others could perhaps give more advice about specific drivers.
Dual coils that can be wired in series could allow more speakers to be paralleled. Otherwise, subdivide this thing to make a separate enclosure for each sub driver.

Don't wire speakers in a common enclosure space to separate amplifier channels. I've seen weird effects on the excursion when I was experimenting with that.

http://www.amazon.com/Loudspeaker-Design-Cookbook-Vance-Dickason/dp/1882580338
is your friend! As a speaker engineer I still use this book.
 

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Your plan sounds a bit complicated - difficult to move, a big project, and somewhat inflexible. As an alternative, why not just make it modular and build known subs flanking a custom equipment rack in the middle. That would allow you to put them next to one another to look like the big integrated console, but they will be easy to move and allow you to build a known design. For example, you could do two of the 32" Marty ported subs which would get you down around 18-19Hz (~24x26x32" each) and then do a 32" tall equipment rack in the middle ~20-40" wide depending on the amount of equipment and wall space.
 
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