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post #11 of 20 Old 09-26-13, 01:21 PM
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Re: Line arrays

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!
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post #12 of 20 Old 09-27-13, 04:28 PM
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Re: Line arrays

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!
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post #13 of 20 Old 09-29-13, 11:37 PM
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Re: Line arrays

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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post #14 of 20 Old 09-30-13, 06:55 PM Thread Starter
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Re: Line arrays

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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post #15 of 20 Old 10-01-13, 07:51 AM
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Re: Line arrays

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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post #16 of 20 Old 11-05-13, 08:10 PM Thread Starter
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Re: Line arrays

136 pounds of primordial IB subwoofer.
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post #17 of 20 Old 01-08-14, 11:39 PM
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Re: Line arrays

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-.../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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post #18 of 20 Old 01-09-14, 10:13 AM Thread Starter
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Re: Line arrays

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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post #19 of 20 Old 01-10-14, 01:45 PM
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Re: Line arrays

Wow that's gonna be a great room. Thanks for sharing and keep up the good work!
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post #20 of 20 Old 08-13-17, 01:42 PM Thread Starter
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Re: Line arrays

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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