Measuring for an IB system... - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 42 Old 06-29-06, 11:37 PM Thread Starter
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Measuring for an IB system...

I thought I would share how I measured for a potential IB system in my home theater room.

EDIT: This is our previous home theater room and we never actually installed the IB system, but it may still be of use to some people wanting an option of how to measure for IB driver placement.


First off I scoped out the potential mounting locations and did some measurements. I lifted one of my PB12-Plus/2's up into the recliner and let it relax for a few minutes... of course then I had to relax myself...





Here are some shots of my attic... the red line is about where my front wall is in the HT room...





It looks like I would have to work around the truss system or move it... where you see that center red line is a 3" pipe running to my projector.





Here are the layers of material from HT ceiling to attic...





Here is an inside shot of the proposed location... those red blocks really need to be spaced further apart since I would probably want to stay with each cutout inside the 16" OC area.





Here is a construction pic before the wall and ceiling sheetrock was installed...

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post #2 of 42 Old 06-29-06, 11:48 PM Thread Starter
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re: Measuring for an IB system...

With the sub reclining and me holding the mic taped to a broom stick in one hand and my other hand working the computer, I ran several sweeps with REW (Room EQ Wizard).

My intentions are to install the IB drivers in a manifold somewhere near the front, so I tested locations all across that front ceiling and got the same response about every two feet. I did not go all the way in the corner because there's no way I could mount it on the outside wall with the roof being so low in the attic. I would have to stay close to center.


Here's five different spots across the ceiling...





I went ahead and setup some filters into my BFD (used for sub equalization) and remeasured just off center....

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post #3 of 42 Old 06-30-06, 12:00 AM Thread Starter
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re: Measuring for an IB system...

I will use 8 drivers and possibly two amps. Probably a couple of EP2500's (2 x 1200 watts @ 2ohms or 2400 watts bridged @ 4ohms).

My tentative plan is to run two manifolds with 4 drivers each. I'll run from my sub pre-out on my receiver to the BFD and split out from the BFD to the two amps. Everything will be mono. The manifolds will be symmetrically located and I will use one channel of the BFD to eq both manifolds at the same time. This has worked very well for me on the SVS subs.

I am favoring the SoundSplinters for their xmax ratings and power handling.
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post #4 of 42 Old 06-30-06, 12:40 AM
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re: Measuring for an IB system...

Sonnie, this is very exciting!
I do have a question however. In most cases, doesn't an IB allignment have lesser Xmax utilization than typical sealed or vented allignment due to the relatively low stress on each driver? You'll have so much cone area with 15" subs and effeciency due to large Vb of an IB enclosure that you'll probably barely use all 23.4mm of Xmax the SS Rl-p 15 has to offer in theory? I could be completely wrong but this is my current understanding of IB,nor do I know if the RL-P 15 is considered a low Qts driver. Also with the low Q associated with IB you'll probably not get slow bass at all! You'll be in for a treat indeed.

Edit: look how flat you've gotten your Fr with just a few filters...you're a pro indeed

If you don't have a BFD for your sub, get one fast!
If you don't have REW, get it now!
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post #5 of 42 Old 06-30-06, 01:31 AM Thread Starter
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re: Measuring for an IB system...

Actually Darren and I were discussing the SS RL-p15 earlier. The dual 4ohm version has a higher Qts of 0.447... which is indeed higher than everything else I have been looking at thus far.

As far as xmax... I am going by what I have been reading about some of the lower xmax drivers being pushed to their limits fairly easily. I may not need the full amount offered by these drivers but I have not seen anything around the minimum of probably 18-20mm that I would at least like to have. I am still looking though. $2000 for 8 drivers is pretty stout.
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post #6 of 42 Old 06-30-06, 08:45 AM
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re: Measuring for an IB system...

For IB Higher XMAX is a very desireable trait...nothing less than 12 or 14 should really be attempted. If you are into high DB bass you'll be glad you bought drivers with the higher XMAX. In your room with 8 of these drivers I'll be surprised if you can see straight sitting in the room. Because these drivers are in an infinite baffle they will be utilizing much of the rated xmax on the sub 20Hz frequencies. There is little to no back pressure... we'll use up the mechanical xmax and never reach the thermal rating. Anything under 12mm will be destroyed in short order when played at reference volumes.

I think you may have misunderstood the more drivers needing more power thing too. Actually the opposite is true... I believe ThomasW touched on that in the cult post. You actually need less power.


Oh and yes, a Qts. of .50 is ideal and the .447 of the dual 4ohm is close.

I wish I could hear your system after you get those SoundSplinters rockin'. You might want to have an aid car standing by if you can.

Last edited by Darren; 06-30-06 at 09:05 AM.
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post #7 of 42 Old 06-30-06, 09:38 AM
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re: Measuring for an IB system...

Sonnie,

An IB is very efficient down low, which means that it doesn't take nearly as much power to reach the same output down low as in a small sealed box. In a sealed/IB system, excursion is output. You don't have one without the other, and 2x the excursion yeilds 6dB more output at a given frequency. I haven't modeled the drivers up yet, but I doubt you would need two of the EP2500's. Your money is typically much better spent on drivers than amps here.

Mark Seaton
"Make no little plans; they have no magic to stir men's blood..." - Daniel H. Burnham
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post #8 of 42 Old 06-30-06, 09:41 AM
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re: Measuring for an IB system...

Hey Mark,

You seem to know a bit about the power required for these drivers. Do you feel 300 watts is enough to see their full potential? Because of the reduced power requirements I'd think it is close if not adequate. I think Sonnie is like me in that I like to ensure I have a decent amount of overhead. I like to have a bit of reserve.
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post #9 of 42 Old 06-30-06, 09:42 AM Thread Starter
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re: Measuring for an IB system...

Right now I'm sittin' on 300 watts per driver running an 8ohm load. But I can get up and let 150 watts go and sit back down on 150 watts per driver.
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post #10 of 42 Old 06-30-06, 09:54 AM
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re: Measuring for an IB system...

Woohoo! I'll be living vicariously through you, Sonnie. I put my IB project on indefinite hold and decided to go with a single sealed RL-P15. I got a dual 4ohm just in case I decide to pick up that IB project again.

Keep the great pics coming!!

Jim
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