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CBT / corner line array thoughts
CBT / corner line array thoughts
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Old 12th October 2017, 04:46 PM   #1
Chris8sirhC is offline Chris8sirhC  United States
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Default CBT / corner line array thoughts

I've been out of the diy audio hobby for a bit now. I've been focused on a small business I started. I'm currently restarting work on a 16nsb + 1 ring radiator corner line array, but alot has changed knowledge wise since I began the project. I have some thoughts and ideas of like to run by you guys relating to both CBT and corner line arrays.

1) in some sense a true floor to ceiling line array comes close to approximating a sliver of a curve from a point source very far away, esp when you factor in floor and ceiling reflections. Is this true at all? Could something like the picture below bridge the gap between the two concepts? Basically you slightly curve the corner array and have angled ceiling and floor reflectors to make the reflections follow the curve. I have a crude picture below.

2) The next thought relates to doing a multi way corner line array. Getting the drivers as close to the corner as possible is optimal, but I'm guessing the lower you go, the further from the corner it can be without losing anything. Why not put the tweeter line way back in the corner, and have the lower end further out, at the same time creating directional control for the tweeter line?

3) The third thought relates to CBT arrays. It seems like having two parallel rows is less than optimal since they aren't resting on the same sphere. Wouldn't it be better to have a separate thin tweeter row just in front of the woofer line. The curve of the tweeter line will be broader than the woofer line curve since it's further from the theoretical point source. With such incredible polar response coming from CBT arrays, as long as you factor in a delay, how far apart could the rows be?

4) array center to center spacing vs polar response of each driver. Has there been any research into how much a narrow vs wide polar response affects the necessary center to center spacing of drivers in an array? I'm guessing an array of laser straight polar responses requires closer c2c than a wide 180 degree polar response at all frequencies.
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File Type: jpg 20171010_100520.jpg (611.9 KB, 129 views)
File Type: jpg 20171012_112405.jpg (329.3 KB, 126 views)
File Type: jpg 20171012_112410.jpg (362.7 KB, 123 views)

Last edited by Chris8sirhC; 12th October 2017 at 09:55 PM. Reason: More
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Old 12th October 2017, 05:49 PM   #2
Chris8sirhC is offline Chris8sirhC  United States
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1) continued: what heigth is the optimal position for the "center" of the curve? Middle of the room, golden ratio between floor and ceiling, listening height?
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Old 12th October 2017, 09:17 PM   #3
Chris8sirhC is offline Chris8sirhC  United States
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And should the full volume drivers be in the center, vs on the floor like regular cbt?
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Old 13th October 2017, 11:01 AM   #4
AllenB is offline AllenB  Australia
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Looking at your first image, and presuming the ends are close to the floor and ceiling, there will be a reflection from these surfaces unless you end the line on them and normal to them. Ie, an array would work into free space but when you need a longer line, and this won't see that free space in a real listening room, you need to work with the surfaces. This means either using a curved line from the floor that ends in an open space part way up the room (or just a small line in the middle) or using a straight line from floor to ceiling.

Although this second option gives an infinite source distance, the room (which is a confined space, and an odd space wrt the expansion of sound) dictates the straight line, which shouldn't be shaded, and all expansion will be in the horizontal dimension.
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Old 13th October 2017, 11:08 AM   #5
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by Chris8sirhC View Post
2) The next thought relates to doing a multi way corner line array. Getting the drivers as close to the corner as possible is optimal, but I'm guessing the lower you go, the further from the corner it can be without losing anything. Why not put the tweeter line way back in the corner, and have the lower end further out, at the same time creating directional control for the tweeter line?
The one thing you have going for you here is that you can waveguide high frequencies with a finite guide built into the other parts of the speaker in some creative way.

It isn't a perfect situation. Multi-way in a corner is (among other things) about allocating the free space vs utilising the surfaces, carefully.

It isn't possible to put un-folded waveguiding into a corner in a way that doesn't mess up the highest frequencies without either cutting into the wall to mount the drivers behind the corner, or building the HF guide to be self contained.
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Old 13th October 2017, 05:44 PM   #6
Chris8sirhC is offline Chris8sirhC  United States
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Quote:
Originally Posted by AllenB View Post
Looking at your first image, and presuming the ends are close to the floor and ceiling, there will be a reflection from these surfaces unless you end the line on them and normal to them. .
Right, that's by design to take advantage of some of the benefits of true floor to ceiling line arrays. With the curve and reflectors, at least the first reflection follows the shape of the theoretical curve.
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Last edited by Chris8sirhC; 13th October 2017 at 05:47 PM.
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Old 13th October 2017, 06:48 PM   #7
Chris8sirhC is offline Chris8sirhC  United States
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Quote:
Originally Posted by AllenB View Post
The one thing you have going for you here is that you can waveguide high frequencies with a finite guide built into the other parts of the speaker in some creative way.

It isn't a perfect situation. Multi-way in a corner is (among other things) about allocating the free space vs utilising the surfaces, carefully.

It isn't possible to put un-folded waveguiding into a corner in a way that doesn't mess up the highest frequencies without either cutting into the wall to mount the drivers behind the corner, or building the HF guide to be self contained.
I just had some time to read through some of the theory on how the synergy horns work, and it would seem like integrating the mids and highs that way would be beneficial. I'm pretty sold on the synergy concept at the moment, and I'm curious how well that could integrate into a floor to ceiling corner line array. Obviously it would involve building into the wall around the corner for a permanent install, but possibly a bulge in the throat for the mid and woofer columns wouldn't hurt fr too much.

For a traditional 3 way synergy, has anybody thought about using the b&g planar range? Their shape etc should make it easier to mount the mids close to the start of the throat vs normal drivers, plus they have very low distortion and high efficiency. In addition, the square shape of the neo3 seems perfect for a clean mount into the throat of a square wooden horn.

Last edited by Chris8sirhC; 13th October 2017 at 06:58 PM.
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Old 13th October 2017, 11:08 PM   #8
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by Chris8sirhC View Post
Right, that's by design to take advantage of some of the benefits of true floor to ceiling line arrays. With the curve and reflectors, at least the first reflection follows the shape of the theoretical curve.
The floor and ceiling make the line behave like a larger one.. but only in one respect, and for this to work it requires the surface/s to cooperate so as not to lose this energy to a higher order mode. Since the room never deviates from constant floor and/or ceiling height there should be no call for vertical gradients or independent vertical travelling energy, but on the other hand any free end of a CBT calls for free space as that is the purpose of the shading.
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Old 14th October 2017, 03:15 AM   #9
Chris8sirhC is offline Chris8sirhC  United States
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Ah, gotcha. I haven't fully read through the cbt papers yet. What do you think about spacing out the various channels as long as they follow the same point source sphere (with appropriate delays)?
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Old 14th October 2017, 03:17 AM   #10
Chris8sirhC is offline Chris8sirhC  United States
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I mainly like that concept from a artistic / architectural / marketing perspective. Imagine a sphere 18" sub in the corner, a small highly arched mid bass in front of it, a larger flatter midrange array in front of that, and finally a taller flatter tweeter line, maybe even spaced out a foot and not in a straight line.
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