Floor-to-ceiling array vs CBT

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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 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.

MisterTwister said:
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.
 
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.
 
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!
 
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.
 
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.
 
I am very happy with the performance of my floor to ceiling line array, but I haven't listened to a CBT array yet. I believe the CBT design ignores the problem of ceiling reflections, were a full line does not.

Actually if I understand things correctly (and I may not), it makes better use of them and is part of the reason for the characteristic curve and the power shading on the drivers as they curve. They aren't designed like they are simply because of someone's pet hobby horse as to what makes for good sound reproduction, there does appear to be quite a bit of research and experimentation behind them.

http://www.parts-express.com/cbt36/#
PartsExpress said:
Specifically Designed to Eliminate the Detrimental Effects of Floor Reflections

The CBT36 has been specifically designed to operate over a reflective ground plane and does not suffer from destructive floor-bounce effects. The curved line array of 72 tweeters extends all the way down to the floor to take advantage of the ground-plane acoustic reflection. Effectively the floor provides a reflective surface that acoustically extends the array below floor level and thus creates an array that is over 10 feet tall and controls vertical coverage and directivity down to below 160 Hz!

The Vertical and Horizontal Coverage of the CBT36 Greatly Reduces Ceiling and Wall Reflections

The above-the-floor vertical coverage of the CBT36 is a narrow 28° which is extremely stable with frequency. This greatly reduces ceiling reflections as compared to a typical box style system. In addition, the horizontal coverage which is very broad narrows as you go around the side of the system, which also significantly minimizes side wall reflections.
 
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A domestic line array or cbt speakers concentrate on vertical directivity but mostly they completely disregard the principles of even horizontal directivity! I simply just don't like the hype around them... First of all, we have our ears placed horizontally for stereophonic localization, we walk - don't fly etc.

Here is horizontal 0¤ vs 30¤ of the Selah Audio CBT lindked above. 6dB dip around 2kHz at 30¤ is really really bad! And the speaker is not symmetrical - I suppose this is the better side!

An externally hosted image should be here but it was not working when we last tested it.


It would be so simple to make these better, it is so hard for me to understand this dilemma. But I don't want this kind of poles in my room... I just keep on nagging about this:smirk:
 
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A domestic line array or cbt speakers concentrate on vertical directivity but mostly they completely disregard the principles of even horizontal directivity! I simply just don't like the hype around them... First of all, we have our ears placed horizontally for stereophonic localization, we walk - don't fly etc.

Here is horizontal 0¤ vs 30¤ of the Selah Audio CBT lindked above. 6dB dip around 2kHz at 30¤ is really really bad! And the speaker is not symmetrical - I suppose this is the better side!

An externally hosted image should be here but it was not working when we last tested it.


It would be so simple to make these better, it is so hard for me to understand this dilemma. But I don't want this kind of poles in my room... I just keep on nagging about this:smirk:

Speakers are inherently flawed devices and that's even before you drop them into a room which is never designed with audio reproduction in mind (Would you want to live in an anechoic chamber?). There are going to be trade offs, compromises, advantages and disadvantages to any set up no matter how much money you spend or how they are designed.

How is it you think they could be made better?
 
What speaker has "even horizontal directivity!"? And at what frequencies? Don't all speakers will become directional at some point, and many highly regarded speakers have narrow radiation patterns, both vertically and horizontally. Electrostatics and planers for example.
 
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What speaker has "even horizontal directivity!"?

Well at least according to the marketing information the CBTs are. Have you read any of the technical papers on them?

I believe the SEOS/Gedde style speakers are supposed to as well.

Though they are certainly NOT going to appeal to anyone who cares about how the speaker looks.

This is out of my area of expertise though.
 
The vertical problems are the same when placing drivers side by side whether it is a CBT or straight array. The trick is to get the crossover point as low as possible and the mids as close to the tweeter as possible. It can be done, but that's not the topic of this thread.

I am interested in vertical polars of a floor to ceiling line array. Does anyone have them?
 
The full height line arrays may be more rare than I new. People talk about them from time to time, but it seems to be mostly theory.

Maybe I will make a quick and dirty prototype with cheap full rangers to have a look at the performance from the mid range and down. We know the upper range from straight arrays will be good from Keele's simulations. It would be interesting to see where in frequency vertical control is lost with an array coupled to a reflecting floor and ceiling, if it would be lost at all.
 
The vertical problems are the same when placing drivers side by side whether it is a CBT or straight array. The trick is to get the crossover point as low as possible and the mids as close to the tweeter as possible. It can be done, but that's not the topic of this thread.

I am interested in vertical polars of a floor to ceiling line array. Does anyone have them?

I meant of course horizontal problems.
 
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