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Discussion Starter #1
Considering an IB subwoofer for my home theater.

Directly behind the theater's screen wall is a ~670ft^3 closet. I think I'm good to go on the 10xVas issue.

I would prefer to use a 4x line array to minimize intrusion into the closet, and I think the four drivers equipped with wire mesh grills would be add a real macho look to my theater.

In looking through the forum here, it appears that line arrays are not well regarded.

The screen wall is sheathed with 5/8 OSB and a layer of 5/8 drywall. Compared to standard construction, this wall is very solid.

Is there any reasonable way to use a line array, or should I bite the bullet, go with a manifold and live with the closet intrusion?
 

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I have to preface this comment that I'm not coming from any type of experience background other than my engineering background, but a manifold would be much better due to the ability to oppose the drivers which would significantly reduce the amount of work you would need to do to keep everything inert and solid. A line array would need a lot of bracing to keep all that energy moving cones and air and not the wall (which even well-braced I would expect to move and vibrate to some extent).
 

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Discussion Starter #3
OK. Here's what my theater look like in Sketchup with 4x15s and two manifolds.

Probably the weirdest thing here is the 2x4 running through the middle of the manifold output area. The wall is sheathed with a layer of 5/8 OSB, then 5/8 drywall. Structurally, I could probably get away with cutting out this 2x4, but would really rather not. Seems like the wrong thing to do given the nature of IB subwoofers.

Any comments?
 

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I like the mockup! The big timber beams give it a very cool look :T

I believe you need to make sure that your manifold opening area is equal to or greater than the drivers' area. If your openings meet that even with the 2x4 there, you should be good. As for what effect it may have soundwise, I don't know. Regardless, I wouldn't take the 2x4 portion out; I would adjust the positioning or manifold size to get the proper openings rather than deal with potentially load bearing members.
 

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Discussion Starter #5
The wall is not load bearing... I know that because I installed it myself.

I do need to make sure I'm OK with Sd... but that's easy. I've got room to make
the manifold taller and wider if need be.
 

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Cool. Then the next thing I would ask is how you will install the drivers. You have the drivers inboard in the manifolds, but no detail whether installed from exterior space or installed into manifolds. If you are installing into the manifold, and don't want to cut out the 2x4s, I would do a sanity check that you have clearance to get the drivers in through the gap. :)

What are you doing to cover the manifold openings? Cloth grilles, perf metal sheeting?
 

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Discussion Starter #7
Although not apparent from the photos, the intention is to load the drivers from the back side. The driver manufacturers don't seem to supply cut sheets, so the precise details of driver mounting will have to wait until the physical drivers are in hand.

The "infinite" baffle is an unfinished storage area. Appearances not particularly important. Probably just a metal grill to keep feet out of the drivers. One thing I have to pay attention to is the access door to this unfinished storage area is somewhat narrow. Hauling the manifolds into the storage area might be a problem. If push comes to shove, I can assemble the manifolds in the storage area.

I was planning on using 3/4 birch ply for the manifolds. I've seen some suggestions that this is insufficient. Given the relatively small size, and that the open end will be securely bolted to a very strong wall, more than 3/4 birch ply seems like overkill??

The plan is for the front (open end) side of the manifolds will be covered with the same material I'm using for the screen wall, which will likely not be "grille cloth". With the extreme air movement generated by the IB subwoofer, this could be a problem??
 

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Discussion Starter #8
And one more thing...

It seems the my choice of drivers is AE or FiCar. Any other viable alternatives?

AE and FiCar prices about the same. Any opinions here?
 

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I can only speak to the birch ply question. I don't know how that would be insufficient. 3/4" ply is extremely strong (even junky ply from Home Depot). What it comes to is structure layout. Big panels with no bracing, yeah, you would have a problem, and it would be mitigated less with adding another layer of ply than just properly bracing and building. You can glue bracing ribs on panels to increase rigidity.

If you can design to build then install manifolds without getting stuck in the door, I think you will have a better chance for success than building "on-site" in the storage area. Another alternative to going in through the door would be roughing out the drywall openings and sliding the manifolds through.

As for the screen wall - how close are the manifold openings to the screen? Others will have to chime in here, but I would give a swag that if the distance between your screen and the openings >= diagonal of one of the manifold openings, you are good.

Take a look at Prof.'s HT build with his horn fronts and sub. Granted this isn't apples to apples, but looks like his screen is butted right up to his fronts and sub.
 

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Discussion Starter #10
BD55

Attached find a current picture of the theater. Not a great picture, but you can see its a bit more than a Sketchup rendering and its way to late to move manifolds through the walls.

Assembling the manifolds in the storage space is not such a bad thing. The worst part is access to the storage space requires a traversal of the wine cellar which is a no-no :nono: .

I am _not_ using an AT screen. IB Sub to screen distance is not the question. The IB Sub openings will be below the screen. I would like to cover up the IB sub openings. The wall behind the screen will be covered in fabric. I would like to hide the subs behind this fabric. I'm worried that this fabric won't be acoustically transparent enough with the extreme IB sub airflow.

And little more background about how I got to where I am... The original plan was to install two "in ceiling" off the shelf subs in the soffits that are just barely visible in the top of the picture. As I started to seriously consider this, several issues became apparent. (at the risk of offending an owner :D) I looked at the in ceiling offerings and decided than in addition being lame, they're rather expensive. Also the soffits are within the acoustic envelope and are not heavily built. I'm concerned that the subs will rattle, or I will have to do a bunch of work to prevent rattling.

Looked into the IB Sub thing and I have a pretty good "infinite" baffle, but I didn't originally plan for an IB Sub... so I've some challenges.

The Bignordique
 

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Gotcha, thanks for clarifying. I was thinking you were using an AT screen. Ok, so the question is whether covering the openings will cause a problem - whether that be reducing output, or whistling, etc., right? A couple examples I've seen with quad 15"s used 16x20" A/C return vents as coverings and noted no rattling of the screen (2' away) or the vent itself - just the projector.

Properly mounted and gasketed to prevent rattles, I think you can get away with most anything for a covering.

After this install you will have to do a lot to prevent rattles...in the room! :hsd:
 

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A few things from my experience:
  1. A manifold opening equal to the combined Sd of all the drivers is NOT required. I'm at about 1.5 Sd of one driver for my two driver manifolds and it works great. There are many documented builds that do not adhere to this rule and turned out fantastic.
  2. The 2x4 in the manifold opening can either stay or go. I chose to eliminate it in my build. The manifold itself is structure replacing the 2x4 and it is stronger now than it was before. Looks much better without when I take the grills off to show off my subs.
  3. AE IB drivers are not really an option. I don't believe they are being made. You would have to find them second hand. Other options include Dayton, Stereo Integrity, RE XXX. I found FiCar to be the best option for me. I do not regret my purchase in any way, they are killer!
  4. I found that installing horizontal cross members between vertical 2x4's helped with front wall vibrations considerably, at least between the vertical members that are adjacent to the manifolds
  5. 3/4" ply will be fine. Many suggest two layers of 3/4" ply but I believe it is overkill, especially if the panel you are mounting the driver to is just larger than the driver itself. I have zero issues with a single layer of 3/4" ply and my 18" drivers.
I think you'll be much happier with the route you are taking than you would have with the so-called in wall subs! :T
 

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Check out my "Christmas Build" in this same forum. It is a 4x18" driver line array and it has 0 vibrations because it is braced by the concrete under it. The sub does not vibrate at all - but the walls do. I would not recommend a line array unless it is braced against concrete(or something completely solid) and you have a thick baffle.

The cool factor is off the charts - people just freak out when they come over. I did overbuild, so you would not have to go the lengths I did.
 

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Discussion Starter #14
I absolutely adore SketchUp. Allows me to become confident about various low level mechanical issues and then think about the higher order issues.

I have two objections to the location shown in the previous renderings. The manifolds significantly impact the usability of the storage space. And, I would need to come up with some acoustically transparent vent for the output ports of the manifolds.

I could leave the output side of the manifolds open. That's pretty macho. Maybe too macho. Any covering needs to be pretty solid so it won't rattle.

So I have a new idea, move the manifolds to a high spot. Hi enough so that I can walk under them. And, put them behind an already planned fabric enclosure with significant distance from the port to the fabric.

Although various doors, framing, etc make it tight, the port cross section is >2x Sd of a single driver.

We have "expansive soils" in Northern Colorado. Hence the stage wall hangs from the ceiling, and has these relatively small pins that hold the bottom of the wall in place. The attachment of the wall to the ceiling is more solid than the "pinned" bottom. So I think that's a plus as well.

Comments?
 

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The new configuration you have will induce a bit more vibration than completely opposed, but I think it would be fairly minimal. The closer you have the drivers to full-opposed (i.e. the axes of the drivers are co-linear), the better cancellation you will have.

With the way you described the pinning/structure of the wall, I think you will have a better setup up high (though it probably won't be too fun lugging the drivers up there :) ).
 

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How are you coming along? I got my best response with two manifolds 1/4 the length of the front wall from the corners. You might get good response in the front corners as well. Pairing them up in the middle would probably be the least ideal placement. I think either close to the floor or close to the ceiling would be OK. Best to use a pair of small sealed subs if you have them to measure response at proposed locations before final installation. If you can't pull that off you can put a sealed sub on your sofa and measure the response at the proposed locations, you just won't get a summed response.

As far as covering manifold openings I used a double layer of this very inexpensive, very nice looking upholstery fabric from jo-ann for $1.99/yd. http://www.joann.com/utility-fabric-upholstery-underlining/10173300.html. Very breathable and looks and sounds great. I'm using it to cover my manifold openings and to cover my acoustic panels and other acoustic treatments in the room.
 

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Discussion Starter #18
The mechanical situation was fairly constrained. Best place for the subs was in the upper corners of the screen wall.

Included a picture. The subs/manifolds are mostly visible as the the light colored boxes near the corners.

When its all done, the subs will be behind some fabric covered frames. You can see one of the as yet uncovered frames on the right side.

I installed some LED strip lights inside the manifolds. When the lights are off, the manifolds are not visible behind the fabric covered frames. When I turn the lights on, you can make out the manifolds and the drivers. This is shown in the second picture.

Haven't tried to measure response yet. You can see, the room is not done yet (pant, pant, pant). Fer sure, they can rattle the walls though.

llj
 

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Discussion Starter #20
Sheesh... finally getting around to using REW on my room. Had to re-acquaint myself with the hometheatershack.

Certainly interesting to look back almost 4 years to see what I was doing back in those days.

Yes, my HT is still incomplete. I work on it when everything else is done.

But... it is now sporting this "QRD sculpture" and a Linux based home automation controller. Both of my own manufacture.

Uttering things like grep and awk whilst ssh'ed into your theater controller is thrill that's hard to describe :).

The IB subwoofers are basically insane. I've never dared turn the iNuke above about 4. I'm certain it would shake the house apart if I took em to eleven. A movie with a good LFE makes hair are your arms vibrate, even at relatively modest volumes. Its a pretty strange sensation.

I did order the carpet for it last week, and I'm in negotiations with _High Command_ on the fabric that will soon adorn the walls. I'm definitely in the home stretch.

I'm sure some of you are wondering what a "QRD sculpture" is. I was gonna include a .mov, but the forum won't allow that. This "QRD Sculpture" is a 28x21 array of 3D printed boxes arranged as a QRD. Each box has an individually controllable RGB LED inside. The attached photo doesn't really do it justice... but it is what it is.

Big
 

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