Floor-to-ceiling array vs CBT - diyAudio
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Old 9th October 2013, 02:25 PM   #1
jeno is offline jeno  Norway
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Default Floor-to-ceiling array vs CBT

I have been investigating the CBT concept for some time and find it intriguing. Keele's simulations show the supremacy of the CBT over straight arrays regarding vertical directivity and uniformity.

However I sometimes see the claim that a floor-to-ceiling array will overcome the problems of straight arrays and eliminate the need for a CBT?

Is everyone in agreement that this is correct?
Does the floor and ceiling need to have special acoustic properties to act as "acoustic mirrors"?
Are there any measurements on the subject?

The reason I ask is that building a straight array would be much easier than building a CBT. It would also have higher spl. It could also stand against a wall and use longer ribbon or planar drivers, wich would be impossible with a curved array.

Any input?
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Old 9th October 2013, 02:58 PM   #2
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what is CBT?
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Old 9th October 2013, 03:07 PM   #3
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Quote:
Originally Posted by jeno View Post
I have been investigating the CBT concept for some time and find it intriguing. Keele's simulations show the supremacy of the CBT over straight arrays regarding vertical directivity and uniformity.

However I sometimes see the claim that a floor-to-ceiling array will overcome the problems of straight arrays and eliminate the need for a CBT?

Is everyone in agreement that this is correct?
Does the floor and ceiling need to have special acoustic properties to act as "acoustic mirrors"?
Are there any measurements on the subject?

The reason I ask is that building a straight array would be much easier than building a CBT. It would also have higher spl. It could also stand against a wall and use longer ribbon or planar drivers, wich would be impossible with a curved array.

Any input?
I'm not sure how extending an already very tall vertical line array a few more feet is going to dramatically change or fix any issues with one.

OTOH, it sounds like you are also talking about a very high end speaker in either case, so you are probably quibbling over the last 1% of performance for the most part.

Quote:
Originally Posted by MisterTwister
what is CBT?
Parts Express presents the CBT36 Line Array Speaker System

It's a line array that is curved back with some sort of power shading as the array curves.
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Old 9th October 2013, 03:09 PM   #4
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Constant Beam-width Transducer. Don Keele is the man who is most often associated with them.

Keith
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Old 9th October 2013, 04:11 PM   #5
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Well, there's this idea: The Murphy Corner-Line-Array Home Page
I guess it's a matter of whether you want to approximate a point or a line.
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Old 9th October 2013, 04:22 PM   #6
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If you have a listening space with relatively "low" ceilings and hard reflective surfaces (floor and ceiling are hard and smooth) then yes, a line array that spans the space from floor to ceiling (drivers all the way to the floor and ceiling boundaries with separation L and the ends located L/2 from floor or ceiling boundary) will be very effective if your listening position is sufficiently far enough away. This is because the image of the speakers reflected off of the ceiling and floor gives rise to an "infinite" line. The problems with line arrays arises mostly because they are finite and so an interference pattern forms. No such problem with an "infinite" line array...

The CBT uses the floor as a reflecting surface. The curve of the CBT is designed to mimic a "slice" of the upper half of a sphere, the lower half being generated by the reflection from the floor.
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Old 9th October 2013, 04:28 PM   #7
flg is offline flg  United States
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I would think, before you comment on this thread, not excluding the starter, that you would have read the Jim Griffon paper, the JBL paper, the David smith paper, etc., etc., etc.
Ideally, you've also heard some of these monsters???
You just can't keep bringing up the same questions over and over without searching, reading, experiencing, etc. Com'on people.
Line array's are cool. They will never go anywhere with the constant restarting of the same thread questions and desire for dialogue.
Go buy some buy-out speakers and give it a try, but read first!
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Old 9th October 2013, 06:28 PM   #8
jeno is offline jeno  Norway
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Quote:
Originally Posted by Generic George View Post
I'm not sure how extending an already very tall vertical line array a few more feet is going to dramatically change or fix any issues with one.
Well, the idea is that the line will be virtually infinite, but I'm not sure how well it works in real life.

Of course I could just buy some drivers and find out by myself, but I would like to do some qualified design choices before I start.

I have of course listened to a lot of line sources, but none of "infinite" length. I have not heard any CBT yet, but I guess I will before I start any project. I have also read the Griffin paper and all of Keele's CBT papers as well as other papers and is well aware of the term "near field" and "far field" of line arrays. I want if possible to have "near field" in the whole room.
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Old 9th October 2013, 07:32 PM   #9
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The version wt the RAAL/Ilum is on page 4.

He's also got the final product referenced on his web site.

ArcArray

Last edited by Generic George; 9th October 2013 at 07:37 PM.
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Old 10th October 2013, 03:18 PM   #10
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Originally Posted by Generic George View Post
The version wt the RAAL/Ilum is on page 4.

He's also got the final product referenced on his web site.

ArcArray
Sorry somehow part of that post got deleted.

Rick Craig has built some CBT in cooperation with Keele. As well as other line arrays, both types with some very high end parts.

You might want to consult with him. He charges extremely reasonable fees for designing bespoke speakers and clearly has a fair amount of experience wt arrays of both types.
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