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post #91 of 129 Old 01-24-2014, 11:31 AM
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I skimmed through that thread Rick, and I doubt the GameChanger got a good position. If they measure as well as CBT36, I would expected from own experience they would measure flatter then the others. Perhaps smoothing is covering up something, but overall they look quite similar. Comparisons like that are difficult. One needs to optimiz position for the speakers IMO. Doesn't look like that was done. They other speakers had the same position, but what seems like a small wall barrier on each side certainly isn't good for a speaker with wide dispersion.



Have you produced a taller speaker with Raal ribbons Rick? I've only seen the one with the woofer at the bottom (ArcArray).
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post #92 of 129 Old 01-24-2014, 12:08 PM
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Originally Posted by omholt View Post

@maxmercy

Ok. I'm a little uncertain how to calculate the SPL since it's a line array. A SPL calculator gives me 105,8 dB with two speakers at 3 feet with 200W. But that's with a regular speaker which looses -6 dB pr meter. With a distance of 6 feet, the max SPL should be around 102 dB. Ok, that's what you said.

What I meant by "13-14 dB at 8 Khz" or which is now corrected to 12 dB (102 -90) is what peaks they can tolerare if I'm playing as loud as at 90 dB. And again, I would refute that high peaks so high in frequency happens much in music. Like I said earlier, that would burn up many tweeters in speakers. High peaks are more common much lower in frequency and as you know the SPL capability of CBT36 goes up. At 800 Hz it's 89 dB and at 300 Hz it's 94 dB. Also, an average listening level of 90 dB is quite high. Most probably listen more in the 80-85 dB level, thus a max of 102 dB is sufficient with a normal listening window. Overall, it's not much of limitation for home use at all, unless the distance is great or if you the type of guy that cranks up the volume to 100 dB. Sure, then you need a lot more power a more efficient speaker.

Anyway, I got the feeling that you were saying that SPL was a serious restriction with the CBT design itself. But look like you agree that with higher sensitive drivers it isn't really an issue at all but more related to cost. The CBT36XL has been mentioned and should be able to play much louder in the very highs. If it's needed or not, depends on the usage.

About the waveguide speaker. Yes, the woofer brings the overall sensitivity down to 97 dB. Still, it gives an impression of the potential limitation of sensitivy with the CBT36. The CBTs has much more energy and are far more transparent sounding in the highs. Listening to a guitar, a flute etc, the waveguide speaker is simply not able to reproduce it like the CBT36 does with a feeling that you are listening to a real instrument. I don't think you can say for certain that higher sensitivty with CBTs will yield better sound. Maybe, maybe not. It's something very else when the speaker has a large group of drivers as oppose to a single one. I believe thermal modulation matters (nonlinear distortion isn't considered an issue) and it's the reason why higher sensitivty speaker sound more effortless. But with 144 drivers as oppose to two, I'm not so sure thermal modulation is a problem at all.

Yes. You not only avoid vertical specular reflections and floor bounce, you also get a very even frequency response down to schroeder. I have had other speakers with controlled directivity but not so far down in frequency. The result is that the CBT36s has given me the flattes response I've ever had. Even in a small room with a low cathedral ceilling, I'm close to get the graph within +/-3dB with 24 oct. smoothing (using two subs). They are also they only speakers I've heard that I thought sounded very good with no sidewall treatment in a narrow room. I believe that's because the horizontal response is so even which, despite of reflections, makes the speakers sound natural. A speaker with only CD above 1KHz sound weird to me without sidewall treatment. The only other speaker I know can give controlled directivity down to schroeder for home use is a corner horn. Anything else, end up being too large for homes in most cases.

The corner horn like Klipsch Jubilee is very interesting though and something I'm considering getting for a setup nr. 2. smile.gif

Even though the SPL capability of the CBT36 is very high in the lower registers, it is equalized/wired such that it will run out of headroom in the upper registers first. You are also correct that music, movies and most content contain most of their energy in the lower registers. I also agree with Rick that the power response is such that horizontal reflections will not be as coloured as with other speaker designs. I am sure that a large CBT array, well designed an implemented, will sound effortless. But it is not necessarily an economical way to generate the SPL requirements for DIY HT in labor, driver count, and power requirements. I am not saying they are bad, and had I the funds, I would build/own a set. I like to know both a design's positives and negatives, though. Without digging into the design, it appears near perfect. But the power requirements and SPL limitations are real, and are often glossed over, hence my responses.

Those CBT45s look lmpressive. I would love to see an HT with those ceiling-mounted behind an AT screen.

JSS
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post #93 of 129 Old 01-25-2014, 07:05 AM - Thread Starter
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Quote:
Originally Posted by omholt View Post

I skimmed through that thread Rick, and I doubt the GameChanger got a good position. If they measure as well as CBT36, I would expected from own experience they would measure flatter then the others. Perhaps smoothing is covering up something, but overall they look quite similar. Comparisons like that are difficult. One needs to optimiz position for the speakers IMO. Doesn't look like that was done. They other speakers had the same position, but what seems like a small wall barrier on each side certainly isn't good for a speaker with wide dispersion.



Have you produced a taller speaker with Raal ribbons Rick? I've only seen the one with the woofer at the bottom (ArcArray).

Yes - challenges from the room including the framing for the screen obstructing the wavefront, walls to the side in close proximity, sub box in the middle to reflect off, and being elevated off the main floor which will affect the loading of the ground plane. The curves taken of each speaker were done with the microphone placed at the point directly behind the rear row of seats. A wider range of measurements at different heights and angles would help show the differences in each design; however, that just wasn't possible with the limited time we had that day. The measurements I have of the Gamechanger on my site were taken with a passive crossover. I need to go back and post them with the DEQX DSP crossover (I used the DEQX at the meeting but didn't add any room correction to keep the playing field even with the other designs).

I've only built the one CBT design using the RAAL ribbons. Obviously the cost factor plays a big part with more ribbons! The dome tweeters also have an advantage in that they control the directivity an octave higher than the Raal. How much of that you can hear is debatable and I do have a preference for ribbons in conventional designs; however, for the cost vs. performance the domes make more sense in a larger array.

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post #94 of 129 Old 01-27-2014, 07:56 PM
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Originally Posted by maxmercy View Post

I also agree with Rick that the power response is such that horizontal reflections will not be as coloured as with other speaker designs.

Why not?

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post #95 of 129 Old 01-28-2014, 12:53 AM
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The CBTs have a very constant and uniform polar response. In other words, the off-axis response changes very little compared to the on-axis response. Thus the reflected energy is much less coloured. One of the results of this is that the vocal is in center even when you move away from the centerline in the room. Even close to sidewalls, I've experiences the vocal still being in center!

Other speakers have to a large degree an off-axis response that changes and isn't constant. The speaker might have wide dispersion in one frequency area, narrow in another, wide again in another are etc. Hence you get a reflected energy with a different spectral content and treatment is an absolutely requirement to get the the speaker to have a correct tonality. We're so used to this that we probably don't notice or think about it. But it's certainly very obvious when you compare a CBT with another speaker.

Something that may improve the polar of a CBT even more would be making it a one-way speaker. Problem would be covering a large frequency area. I 'm curious if a one-way CBT with 2" drivers (TAD beryllium? biggrin.gif) would work well down to 500-400 Hz or lower. Anyone?
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post #96 of 129 Old 01-28-2014, 01:02 AM
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Another thing to add about that. Avoiding floor reflections is also important. To treat the floor reflections properly is very difficult. Most use a thick carpet. The problem with a carpet is that is exhibits a such a high frequency profile as to not be effective as broadband absorption for a traditional speaker. So again you have colouration from the reflected energy from the floor.

With the CBT the floor reflection is a benefit. It is coupled to the floor and the reflection contributes what is effectively the other half of the CBT. So it negates the need for a full arc. This is a great advantage. It effectively eliminates the need for floor treatment. A bare broadband reflective floor surface is optimal!
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post #97 of 129 Old 01-28-2014, 01:33 PM
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Originally Posted by omholt View Post

The CBTs have a very constant and uniform polar response. In other words, the off-axis response changes very little compared to the on-axis response. Thus the reflected energy is much less coloured.

I won't argue with actual results, but I do with the reasoning; the greater the off-axis output, the more room response will be influenced by the spectral character of the room reflections.

Noah
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post #98 of 129 Old 01-28-2014, 02:22 PM
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No. You're mixing two things. There's a difference between high gain reflections which is related to imaging (pin-pointing) and the power response of a speaker. Any speaker needs early reflections attenuated in order to get great imaging. Independently of the dispersion pattern.

Problem with speakers that have a narrow dispersion is a typical collapsing polar response. So while people think they avoid reflections with such a speaker (often horns), the reality is that they only avoid reflections at some frequencies and the result is that spectral content is changed by the room. Some "frequency" reflections are avoided and some are not, hence colouration. With the CBT, the dispersion doesn't change like that. The reflected energy is much more similar to the direct sound. It doesn't matter whether the speaker has a wide or narrow banwidth in that regard. Again, that would be related to imaging and is easily dealt with treatment if one desires that over spaciousness.

Here are two polar plots where you see the dispersion changes and doesn't stay uniform.


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post #99 of 129 Old 01-28-2014, 04:16 PM - Thread Starter
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Originally Posted by noah katz View Post

Why not?

Here's a full arc CBT I helped build for my church here in NC. I had a chance to be in the room (one level, fan-shaped) before it was treated and bare with just a stage and no furniture. When I clapped my hands from center stage there was a significant amount of slap echo from the side walls. After construction was completed the only absorption panels used were placed on the rear wall of the room. I was concerned about the side reflections coloring the sound and thought this would be a problem. After listening a few times I changed my mind as the intelligibility on speech in particular was excellent.


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post #100 of 129 Old 01-28-2014, 04:40 PM
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Here's a full arc CBT I helped build for my church here in NC.
Quite the accomplishment
How long has it been in use now?

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post #101 of 129 Old 01-28-2014, 05:12 PM - Thread Starter
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Quite the accomplishment
How long has it been in use now?

Thanks - many hours of donated labor went into building three of them as well as three smaller stage monitors. There are two sections joined together, each weighing about 250 lbs. with a total of 56 5" woofers and 28 ribbon tweeters. In use about seven years now and no driver failures.

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post #102 of 129 Old 01-28-2014, 05:20 PM
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In use about seven years now and no driver failures.
That in itself says something.
So all parties ( congregation ) are satisfied I presume?

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post #103 of 129 Old 01-28-2014, 05:53 PM - Thread Starter
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That in itself says something.
So all parties ( congregation ) are satisfied I presume?

I think so but I'm not involved with the sound / media team. Most issues usually concern levels and mixes which can vary depending on who's running the board. Uniformity around the room is good but a little adjustment was needed early on to cover the front two rows based on input from those sitting up close.

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post #104 of 129 Old 01-29-2014, 12:36 AM
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That's a huge CBT speaker. Very cool. It's the perfect speaker to cover a large crowd.
Dealing with flutter echo is also an advantage though. Using RPG type binary panels is better for that purpose as oppose to normal absorption panels.
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post #105 of 129 Old 01-29-2014, 02:40 PM
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Originally Posted by omholt View Post

With the CBT, the dispersion doesn't change like that. The reflected energy is much more similar to the direct sound.

It's true that the better power response results in less colored reflections.

It's also true that less reflections would result in a less colored overall response, which was my point.

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post #106 of 129 Old 01-29-2014, 02:58 PM
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Ok. I see. With the CBT you avoid vertical reflections to a large degree but have more sidewall reflections as oppose to a horn speaker with constant directivity low in frequency. Overall, one has less reflections with a horn that has a 30 (vertical) x 45 degrees (horizontal) dispersion. However, it also comes at the cost of a less uniform response.
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post #107 of 129 Old 01-29-2014, 03:49 PM
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Right.

While a WG system has better directivity control over it's effective range, that range stops somewhere in the midrange, while he CBT has less directivity but is more uniform across a wider freq range.

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post #108 of 129 Old 01-30-2014, 12:04 AM
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WG system? You mean waveguide?
A waveguide doesn't have a particular well controlled vertical directivity from what I've seen. Besides, I've never seen a waveguide has CD lower then 800 Hz. Vertical reflections arrive earlier in most rooms and are also considered more detrimental, so the CBT has overall better directivity control then a waveguide IMO.
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post #109 of 129 Old 01-30-2014, 03:17 AM
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Quote:
Originally Posted by omholt View Post

WG system? You mean waveguide?
A waveguide doesn't have a particular well controlled vertical directivity from what I've seen. Besides, I've never seen a waveguide has CD lower then 800 Hz. Vertical reflections arrive earlier in most rooms and are also considered more detrimental, so the CBT has overall better directivity control then a waveguide IMO.

Perhaps the CBT has better vertical directivity, but, are you sure about it having better horizontal directivity? I would expect the waveguide speaker to have a better horizontal pattern coverage.

As far as waveguides being able to hold pattern control and cross a compression driver below 800hz, there are several waveguides that are more than capable of doing this. Take the Seos-24 or Seos-18 for example. The Seos-24 can hold pattern control down to sub 500hz! I am not exactly sure of the Seos-18, but it should be able to hold the pattern control down to 800hz with a decent compression driver.
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post #110 of 129 Old 01-30-2014, 04:53 AM
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Perhaps the CBT has better vertical directivity, but, are you sure about it having better horizontal directivity? I would expect the waveguide speaker to have a better horizontal pattern coverage.
First you have to define "better". And I think the answer has been given to the differences ealier in this thread. The waveguide has a higher Q where it's operating but below the waveguide there's no controlled directivity. The polar is collapsing plus you have some beaming. That leads to a colored reflected energy. There's a good reason why the folks who produce the waveguided often don't show what's happening below the waveguide. The CBT has a lower Q but it's constant. Take you're pick but I know what sounds more natural and correct whether sidewall reflections are dealt with or not. I have both type of speakers.
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As far as waveguides being able to hold pattern control and cross a compression driver below 800hz, there are several waveguides that are more than capable of doing this. Take the Seos-24 or Seos-18 for example. The Seos-24 can hold pattern control down to sub 500hz! I am not exactly sure of the Seos-18, but it should be able to hold the pattern control down to 800hz with a decent compression driver.
Yeah, the Seos-24 seems to have controlled directivity lower. That's the caveat with horns. It requires size in order to achieve controlled directivity low in frequency. Just imagine how big the horn will become for CD down to 200 Hz. The Klipsch Jubilee has CD all the way down to schroeder when corner mounted though. I believe it's a better design then traditional waveguide speakers.
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post #111 of 129 Old 01-30-2014, 11:37 AM
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Quote:
Originally Posted by omholt View Post

A waveguide doesn't have a particular well controlled vertical directivity from what I've seen. Besides, I've never seen a waveguide has CD lower then 800 Hz. Vertical reflections arrive earlier in most rooms and are also considered more detrimental, so the CBT has overall better directivity control then a waveguide IMO.

Yes, CBT has much better vertical directivity control than WG systems.

I would submit that CBT has poor horozontal directivity, as directivity is the opposite of dispersion.

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post #112 of 129 Old 01-31-2014, 09:49 AM
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Originally Posted by noah katz View Post

Yes, CBT has much better vertical directivity control than WG systems.

I would submit that CBT has poor horozontal directivity, as directivity is the opposite of dispersion.


CBT has a lot of drivers, so you could stacket WG systems and then you have better vertical directivity and less HF reflecions vs CBT!
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post #113 of 129 Old 01-31-2014, 11:16 AM - Thread Starter
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CBT has a lot of drivers, so you could stacket WG systems and then you have better vertical directivity and less HF reflecions vs CBT!

Actually the waveguides would have a negative impact on the vertical coverage due to the greater center-to-center spacing. The vertical directivity is very well-controlled with dome tweeters.

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post #114 of 129 Old 01-31-2014, 06:37 PM
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Actually the waveguides would have a negative impact on the vertical coverage due to the greater center-to-center spacing. The vertical directivity is very well-controlled with dome tweeters.

Yes, that may be the case with waveguides indeed having less vertical directivity, but, I think most of us would trade a better vertical directivity speaker for a better horizontal directivity speaker as most folks probably listen to their speakers at ear hight sitting down, which, I am sure you already know, just throwing it out there.
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post #115 of 129 Old 02-01-2014, 12:25 AM
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A waveguide even at a size of 15" has wide and no controlled directivity below 1000-800 Hz and it beams in the highs. To call that a better directivity is a misunderstanding IMO. The result is coloured reflected energy and an unven response below 1000-800 Hz compared to a CBT. Doesn't the frequency respons below 1000-800 Hz count? Sure, it you have a horn and CD down to schroeder, then it's another comparison and a debate. But that's not the case with the popular waveguides people buy. Most buy either 10" or 12" waveguides. A few bigger ones. The result is both uneven frequency response below the waveguide working area (compared to the CBT) and colouration from the room.

I get the impression that people have become a little obsessed with sidewall reflections within a certain frequency window and are not able to see the whole picture (as described above). Add to the fact that the CBT almost avoids vertical reflections which in almost in every room arrive earlier, are considered more detrimental and gives overall gives less early reflections then the waveguide in many rooms, I think one isn't seing things clearly.

One needs a much bigger horn speaker if you want to even out the odds against CBT. Then you have two different speakers for different applications. Which is better here is more related to the type of use.
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post #116 of 129 Old 02-01-2014, 04:58 AM
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Originally Posted by omholt View Post

A waveguide even at a size of 15" has wide and no controlled directivity below 1000-800 Hz and it beams in the highs. To call that a better directivity is a misunderstanding IMO. The result is coloured reflected energy and an unven response below 1000-800 Hz compared to a CBT. Doesn't the frequency respons below 1000-800 Hz count? Sure, it you have a horn and CD down to schroeder, then it's another comparison and a debate. But that's not the case with the popular waveguides people buy. Most buy either 10" or 12" waveguides. A few bigger ones. The result is both uneven frequency response below the waveguide working area (compared to the CBT) and colouration from the room.

I get the impression that people have become a little obsessed with sidewall reflections within a certain frequency window and are not able to see the whole picture (as described above). Add to the fact that the CBT almost avoids vertical reflections which in almost in every room arrive earlier, are considered more detrimental and gives overall gives less early reflections then the waveguide in many rooms, I think one isn't seing things clearly.

One needs a much bigger horn speaker if you want to even out the odds against CBT. Then you have two different speakers for different applications. Which is better here is more related to the type of use.

You are correct, I did not think about the frequencies below the waveguide/compression driver crossover point. I have only limited experience with line arrays, wish that I could afford to build a nice one! I am particularly interested in line arrays with ribbon tweeters. My local speaker shop has some really big McIntosh line arrays that cost like $25,000+ in their show room powered by some ubber expensive McIntosh amps and a McIntish pre-amp. I think that I may try to make my way down there this afternoon and spend some time listening to them!
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post #117 of 129 Old 02-01-2014, 05:02 AM
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Also, just out of curiosity, when designing and building a line array, how do you know what the optimal number of tweeters and mids would be? I can only imagine how nice a RAAL based line array would sound! Just wonder how many of them it would take to give a great SQ? I would also assume that the cheaper Fountek NeoCd3.0 ribbon tweeter would sound terrific in a line array!
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post #118 of 129 Old 02-01-2014, 05:32 AM
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when designing and building a line array, how do you know what the optimal number of tweeters and mids would be?
Since there are a number of options and design variables that depends.
Keele has done a large volume of work and evaluation on arrays ( based of course on fundamental work of early last century - 1930 ).
This includes at least 7 different array implementation, from the simplest original "un-tapered" arrays ( which have directivity that varied ) , to designs that modify directivity through spatial offset and signal conditioning.
In the 80's were prototypes that used the smallest drivers available - headphone elements.
Keele built an array using small headphone drivers prior to his current C.B.T.

EDIT:
Ureda details the design criteria and issues in these frequently referenced
AES papers
that https://engineering.purdue.edu/ece40020/Homework/SomeRefs/Line_Array_Theory.pdf
http://www.nextdigital.com.br/AES2001_Ureda_Line%20Arrays.pdf

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post #119 of 129 Old 02-01-2014, 06:58 AM
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Just in case.
CBT isn't the same as a line-array. Read Don Keele's papers. A regular line-array has a lot of flaws and not something I would recommend. It's called CBT (constant beamwidt transducer) and gotten it's own name because it's in several ways very different.
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post #120 of 129 Old 02-01-2014, 09:16 AM - Thread Starter
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Quote:
Originally Posted by Martycool007 View Post

Yes, that may be the case with waveguides indeed having less vertical directivity, but, I think most of us would trade a better vertical directivity speaker for a better horizontal directivity speaker as most folks probably listen to their speakers at ear hight sitting down, which, I am sure you already know, just throwing it out there.

Actually I think control of the vertical coverage has been underestimated - maybe because many designs couldn't optimize it so we just kind of gave up on it? It became apparent to me while listening to an acoustic upright bass because the scale of the CBT array sound and placement was much more "real" than a conventional design. With the horizontal coverage of any speaker the bottom line is what the side reflections do to the imaging and tonality at our listening position. One of the common themes of the CBT is that regardless of where I've played them people have commented on the uniformity in the sound from the back to front of the room as well as moving horizontally from side to side. Now if the horizontal coverage pattern was a problem for the tonality and imaging don't you think the comments would be unfavorable?

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