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Old 29th July 2010, 03:28 AM   #51
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There is a whole lot of speculation going on in this thread about the CBT. I have read all of Don's papers, some multiple times, and I personally recommend that you start with the Ground Plane Paper. This will jump start you on understanding his approach because it starts with the full array and then shows how the floor image can be used for half the array.

I think it is important to point out that this technique can be used to design a speaker that can provide both vertical and horizontal control, but the design shown at the beginning of this thread is intended to have a wide horizontal pattern and controlled vertical pattern.

Above the lower cutoff frequency of the array, the vertical beamwidth of this design locks in and remains constant though out the audio band, the horizontal beam width is very wide at all frequencies.

One last comment before this thing times out, the top drivers are at -12dB, the shading occurs in steps of 0, -3, -6, -9, -12dB with a net loss of just under 3dB for the array.

-mk

http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20(2005-10%20AES%20Preprint)%20-%20CBT%20Paper%205.pdf
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Old 29th July 2010, 04:45 AM   #52
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@ panomaniac: Are you sure that the array is attenuated by 12dB at the end, I seem to have read that it was less, but it was a fast read.
That's what Keele's papers say and what he told me. I did not measure it.
Amplitude ONLY, not frequency. Also see post above.
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Old 29th July 2010, 01:30 PM   #53
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The shaded array I have worked with uses synthetic aperture technology which results in half the energy radiated into the 20 degree tall vertical beam. The other half of the energy goes everywhere vertically (the other 160 degrees) and is not very important as the beam is 10dB louder than not in the beam. Horizontal control is left to the midrange and tweeter drivers designed to have the same frequency response on axis and 30 degrees off axis. These two together make a 60 degree wide 20 degree tall rectangular window for the listening area straight in front of the center of the array. As the mids are 6.5 inch and the tweets are 1 inch with lens the directivity of the speaker array is pretty constant from 200Hz-20kHz. First reflections in the room are completely unnoticeable because the direct sound is so much louder, at least 10dB in the main beam/lobe. This is done to eliminate room effects and items in the way of the sound, floor and ceiling bounce, and so on. The result is a speaker where at peak levels of 110dB at the listening position (10 feet) the midranges do not even appear to move. Image is stunning and clarity is extreme. Comparing the sound to highest quality headphones the headphones mask out a lot of the sound and loose a lot of the dynamics hiding popping "P" sound clearly audible on the array, as example.

There are a lot of ways to make arrays and of course some work better at some things than others and some solve problems that others do not, of course. It seems to me it is important to target statements about arrays to a particular style of array as the end results vary with particular designs so widely in this style of speaker system. I have never heard or tested anything so dynamic and alive sounding as a good array. All other speaker methods are much closer to dull lifeless and boring by comparison.
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Old 29th July 2010, 01:44 PM   #54
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All other speaker methods are much closer to dull lifeless and boring by comparison.
Yeah, kinda like real acoustic instruments.



Just poking fun. But line arrays always sound "hyped-up" to me. A lot of fun and spectacular, but not realistic. Comes down to what you like - a matter of taste. Great for rock and other amplified music genres. It's a very popular style.
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Old 29th July 2010, 01:49 PM   #55
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I have never heard or tested anything so dynamic and alive sounding as a good array.
+1

At the conclusion of Don's presentation, he treated us to a recording of fireworks...the finale...the conclusion.

At the end of the day the CBT's were set up for one last go...radial aircraft engines...they were in the room with us, the air being chopped by the blades was palpable...and I have been around aircraft
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Old 29th July 2010, 01:55 PM   #56
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@Pano:

Just like some food tastes good but is not healthy ?

But seriously, i cannot see line arrays lacking "reality" from
their working principle.

But i can see the common 2- or 3 way lacking reality by principle.

Like in everything only the real implementation can be judged and
there may be better and worse ones too.
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Last edited by LineArray; 29th July 2010 at 02:03 PM.
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Old 29th July 2010, 03:22 PM   #57
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My key point is there are a lot of solutions to playing music through speakers from a single full range, like a headphone, to these arrays. Every choice has certain advantages and disadvantages which "weigh in" on the final decision. I believe almost any design has merits not found elsewhere therefore no poopooing any one because some other does not do what that one does.

Everyone is right, it is a matter of taste. I happen to like my speakers to sound like live except in really good short reverb time room from where the conductor stands at the podium. Arrays give me that sound more than any other.

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Old 29th July 2010, 04:01 PM   #58
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@sumaudioguy

Your description of a shaded speaker is interesting, but not quite clear, perhaps you can expand on it and/or provide a diagram??

The idea that a 10dB down major lobe bouncing off a surface is not "noticeable" just isn't accurate. What you might say is that YOU did not find it objectionable??

Take the same speakers outside and listen - you might then just notice how MUCH of a factor the room and the stuff bouncing off the surfaces really is?

-------------------

@ everyone

To keep this in context - I am an advocate of line arrays - having built many in the 70s... (again, see my website Archives section?).

I can tell you that there are many speakers that can "reproduce" very impressive sound levels with low distortion today, line arrays do not have a corner on that aspect.

That Don Keele's speakers work well, is fine with me.

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Old 29th July 2010, 05:52 PM   #59
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Default Modeling of line arrays

Since there seems to be interest in line arrays, here is an AES paper I wrote on the topic. It is a little more basic/broad than Don's and might give you all some useful background.

Had to split the PDF into 4 parts.

David Smith
Attached Files
File Type: pdf Line Arrays Part1.pdf (193.8 KB, 410 views)
File Type: pdf Line Arrays Part2.pdf (195.0 KB, 248 views)
File Type: pdf Line Arrays Part3.pdf (185.3 KB, 227 views)
File Type: pdf Line Arrays Part4.pdf (158.6 KB, 232 views)
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Old 29th July 2010, 07:58 PM   #60
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Originally Posted by sumaudioguy View Post
I believe almost any design has merits not found elsewhere therefore no poopooing any one because some other does not do what that one does.
Quite agree, quite agree. I have my favorites but am constantly surprised by others. I've gotten to the point that I just don't know what's going to come out of a speaker. There are some real surprises in store.

Now I have to put on my "grumpy uncle" hat and talk about the Keele array and demo. I was there, I heard it. He had done some of it the night before, too. It was big, it was loud, it was fun, but it was not all that great. I heard speakers, speakers that were straining at that SPL. And lots of overhang, if that's the term. I.E. cones continuing on when they should have stopped. At least 1/2 that was the sub.

I've heard those engine, cannon and fireworks demo things done sooooo much better. All the dynamics without the sloppiness. It's mind blowing when you hear it. To Keele's credit - his arrays did a great job for their small size. Bravo! <hat's off>

As Sum says, it's a matter of taste. Most speaker systems sound puny to me, and the big ones sound overblown. I hear a velvety, delicate smoothness and subtlety in live acoustic instruments and voice that I rarely hear on speakers. But for rock, pop, reggae, hip-hop who cares? Bigger is better. A matter of taste, for sure.
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