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Old 11th May 2010, 08:04 PM   #21
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Default cannot be done passively

Quote:
Originally Posted by jcx View Post
in the curved array the physical geometry provides the phase shift - only amplitude "shading" is needed - parallel/series diriver combinations are used in some of the physical prototype curved CBT arrays that exist so that they can be driven with a single standard audio power amplifier
A curved array only provides fixed delay between drivers. As you say parallel/series gives amplitude only "shading." My array uses specific filters to derive transfer functions for each driver. I use an amplifier for each driver to control the driver well. The result is then one main lobe with half the radiated energy in that lobe. The other half of the energy goes all over the place and is without directivity or phase. This particular setup has constant vertical directivity from 200Hz up with an included angle of 12 degrees, a DI of 10. The horizontal is controlled by the drivers themselves with a constant included angle of radiation of 60 degrees. It is extremely apparent when moving from the beam to out of the beam, extremely apparent. This cannot be accomplished by bending the line or by passive mechanical treatments. Obviously, constant directivity equalization is required throughout this pass band.
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Old 11th May 2010, 10:09 PM   #22
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I worked on arrays at McIntosh and had very useful improvements of directivity with straight lines and shading techniques. If you add frequency tapering you can do even better.

Certainly an active approach or the use of delay will give you mare variables to play with but don't discount the simpler approaches.

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Old 11th May 2010, 11:03 PM   #23
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In my line array i use a combination of weighting by
driver distance and frequency dependent power tapering
for the vertical control of radiation angle.

The horizontal angle is controled by the witdh of the
open baffle relative to the drivers.

pics show the input voltage of the lower and the upper
driver trio.

Tweeters on the rear are used to compensate
falling back radiation with rising frequency
of the fullrage drivers, they move in antiphase
to maintain dipole operation >3Khz.

All compensation is done passively with very low
phase shift and smooth slope.

lower frequency limit 60-70 Hz depending on
room and position, dipole subwoofer needed.

cutoff to subwoofer -6db /octave at 80 Hz using
PLLXO.
Attached Images
File Type: jpg lower.JPG (32.4 KB, 884 views)
File Type: jpg upper.JPG (32.5 KB, 690 views)
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Last edited by LineArray; 11th May 2010 at 11:12 PM.
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Old 13th May 2010, 03:20 AM   #24
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On his Linkwitz Lab website Dr. Linkwitz has some interesting things to say about the Constant Beamwidth Transducer (CBT) technology. He also includes links to Don Keele's Boston AES CBT presentation earlier this year. I suggest that those interested review Keele's presentation viewgraphs and the movie of his pitch. Linkwitz concludes: "It will be the end of the horn and compression driver in quality critical applications."

Linkwitz-Links
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Old 13th May 2010, 05:37 AM   #25
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Would never discount simple approaches myself however, fancy approaches can achieve fancier results. The simply approach is used widely now for concert setup and almost every big player, Peavey, EV, McCormick, etc., has arrays of the simple kind.

Jim Griffin's mention and going to Linkwitz-Links showed a huge amount of useful information- very cool link, thanks.

As a note, the signal to noise ratio and lack of distortion of the amplifier for every driver array is really astounding. With volume set on "blast" I cannot even see the 6.5" midrange drivers move and that is high pass crossover at 100Hz at -12dB per octave.
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Old 13th May 2010, 05:55 AM   #26
gedlee is offline gedlee  United States
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Quote:
Originally Posted by Jim Griffin View Post
Linkwitz concludes: "It will be the end of the horn and compression driver in quality critical applications."
I'll take that bet. Well "horns" are already dead, but the waveguide era is not going away any time soon.
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Old 13th May 2010, 06:34 AM   #27
soongsc is offline soongsc  Taiwan
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Quote:
Originally Posted by Jim Griffin View Post
On his Linkwitz Lab website Dr. Linkwitz has some interesting things to say about the Constant Beamwidth Transducer (CBT) technology. He also includes links to Don Keele's Boston AES CBT presentation earlier this year. I suggest that those interested review Keele's presentation viewgraphs and the movie of his pitch. Linkwitz concludes: "It will be the end of the horn and compression driver in quality critical applications."

Linkwitz-Links
Reading through some of the information, this approach seems somewhat familiar. Makes me think of some of Ted Jordan's work back in th 80's. I think this is a valid approach for large audiances where high SPL is required. Trying to understand how and what different people listen for, aside from tone balance, it seems that there is a group that listens for dynamics and impact, while a different group will listen for the small details.

The people that hear the details take pleasure in the playing techniques and fingerwork of the player. I have heard people complain that they cannot hear this in most of the so called hi-fi systems.

The people that listen to the overall dynamics and impact might complian it's hard to find a system that delivers such. This is the group that the line array will be appealing to.
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Old 19th July 2010, 04:58 PM   #28
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To learn how Constant Beamwidth speakers really work please visit Don's updated and expanded WEB site (www.dbkeele.com). There you will find all his papers on CBT's. In addition there are test signals and a whole lot more.

I have built several different versions of the CBT and if implemented properly, they behave exactly as describe in these papers and they can compete with any high end system available.
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Old 24th July 2010, 02:59 PM   #29
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Well, I heard Don's arrays. While they may not be the worlds best speaker, they certainly do NOT sound like an AM radio. Even without the sub. And as far as I could tell, everything Don illustrated in his directivity plots, he proved with this speaker. The only obvious problems I heard where that he tended to overdrive them, and his sub was boomy. Can't blame the sub boom on the array!

It's fun to play armchair general and criticize what you haven't heard. Once you've heard it, you might not be so quick to dismiss it.

I've also spent time with the ClairAudient line arrays. No subwoofer there and plenty of bass from those 3" drivers. Not an AM radio sound at all. Not perfect, either, but better than many other speakers.

Jim G can chime in. He was in Dayton too and heard the Keele array.
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Old 24th July 2010, 07:23 PM   #30
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Hey Guys,
you might be interested in this approach.

MLA? Multi-cellular Loudspeaker Array. Martin Audio Ltd.
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