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CBT24 line array speakers
CBT24 line array speakers
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Old 12th August 2017, 08:46 PM   #71
wesayso is offline wesayso  Netherlands
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Go figure, reduced reflections of the side walls compared to conventional speakers. Can anyone figure out why? It isn't magic.
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Old 13th August 2017, 07:11 AM   #72
Omholt is offline Omholt  Norway
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CBT24 line array speakers
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Originally Posted by wesayso View Post
Go figure, reduced reflections of the side walls compared to conventional speakers. Can anyone figure out why? It isn't magic.
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For the ground-plane CBT36 array, this narrowing occurs at floor level! Effectively the bottom of the following balloon is cut off! This is why the horizontal coverage of a CBT array that sprays the side walls is much reduced compared to a conventional speaker, the vertical coverage is very narrow at the sides!
Don is looking at the total reflected energy here, not necessarily the reflections you get exactly at the sweetspot. While a ground plane CBT like CBT36 and 24 have a wide dispersion, they only have it in a small vertical area. As you go down, the dispersion becomes narrower and narrower. While a traditional speaker will be fairly wide in a large vertical area, thus probably spraying the side walls more in total.

However, in the sweetspot you do get reflections from both side walls at ear height with the ground plane CBT36 and 24. And it needs to be treated if one wants the absolutely best imaging, as oppose to a more spacious sound field. A matter of taste. The nice thing about CBT is that it does have a correct tonality even with the side wall reflections due to it's uniformity. And with reflections below a minimum of -20 dB in the vertical plane, the speaker sounds good with little or no treatment in a small room.
A conventional speaker will need much more treatment to sound decent.
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Old 13th August 2017, 09:23 PM   #73
Rick Craig is offline Rick Craig  United States
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Originally Posted by jcx View Post
while I long ago heard a CBT demo at a joint AES, BAS meeting, there wasn't anything to compare to

the floor reflection image extending the array is obvious, but do we want the 'niceness' of the CBT approximating a spherical cap when the virtual center point is on the floor behind the speaker?

monkey coffins on sticks suggest floor (and ceiling?) comb filtering dosen't annoy many enough to do anything about it

I've also heard a tall line souce in a heavily treated, low ceiling room which gave very clear imaging - but the effect was all over the place from recording to recording - as expected with pan potted mixes dominating commercial stereo source
True, the floor and ceiling reflections are something we all have endured, but we never had much of an alternative. Having used CBT's in various environments I think the improved room interface certainly helps. You can also vary the scale (height) to suit your listening preferences. I do find them more realistic sounding than a tall un-shaded array.
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Old 14th August 2017, 09:33 PM   #74
Rick Craig is offline Rick Craig  United States
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Originally Posted by jarvissound View Post
Rick I was contemplating something based on the Dayton AMTPRO-4, which I think would work pretty well as we already use them in our Linkwitz inspired dipoles. The issue is the midwoofers; I'm thinking with the shading and trying to overcome the dipole loss smallish woofers are going to run out of steam pretty quick. I wonder if I can get away with 8 inchers and cross hard about 1.2k????

Pic of our AMT dipole prototypes....which are ok but have issues. One problem is the narrow vertical on that ribbon, which is what got me thinking about these CBT's in the first place.

Thanks for your thoughts Rick.

Brett
Sorry for my late reply. That's a tough combination but you might find it acceptable for your needs. Have you ever listened to the JBL Eon system?
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Old 20th August 2017, 01:17 AM   #75
jarvissound is offline jarvissound  United States
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Sorry for my late reply. That's a tough combination but you might find it acceptable for your needs. Have you ever listened to the JBL Eon system?
Rick I'm not quite following you--what does a JBL Eon have anything to do with what we're talking about here? What is a tough combination?
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Old 21st August 2017, 02:16 PM   #76
Rick Craig is offline Rick Craig  United States
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Originally Posted by jarvissound View Post
Rick I'm not quite following you--what does a JBL Eon have anything to do with what we're talking about here? What is a tough combination?
I was just curious if you had heard their portable line array. I have some friends who need a similar type system for ease of setup and portability.

In regards to your proposed design I was thinking of driver spacing, coverage, impedance, etc. - many things to consider.
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Old 22nd August 2017, 04:27 AM   #77
jarvissound is offline jarvissound  United States
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I've not heard the JBL Eon, but I am well versed in the Bose and have owned the K-Array($$$$$) KR systems. They are small and portable, but ignore the elephant in the room, just like all of these systems: **low frequency and mid-bass pattern control**. All I want is a speaker that illuminates a room roughly similar to how a real instrument does. In theatrical sound that is the goal.

Despite Keele's, and other's, claims of broadband pattern control, none of them actually achieve any semblance of pattern control in the lower octaves, vertical or horizontal. In the horizontal, 180 degrees from 600hz up and 360 degrees 600hz down is NOT constant directivity in my book, while the upper octaves are 120 degrees or less. Can you imagine what a sonogram for those looks like? Klingon "Bird of Prey" comes to mind.

Last time I checked there are five octaves between 20hz and 640 hz. That is half of the audible spectrum.

Obviously those of us in PA/Theatrical audio benefit from mid-bass pattern control. Could it be that the holy grail of home audio is an Econowave design with a dipole bass section??? For theatre sound that seems to be the case.

Brett
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Old 22nd August 2017, 08:43 AM   #78
keyser is offline keyser  Netherlands
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What about a tall CBT with cardioid mid and a waveguide on the tweeters? Of course you'd still have the increase in vertical baeamwidth below a certain frequency, but if the array is sufficiently tall you may be able to push that to around the Schroeder frequency of you room. If I ever build a speaker for the hobby again, that would probably be it.
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Old 22nd August 2017, 07:00 PM   #79
Grasso789 is offline Grasso789  Germany
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Originally Posted by jarvissound View Post
All I want is a speaker that illuminates a room roughly similar to how a real instrument does.
My spanish guitar radiates the bass and tenor in all directions. Even an uprite bass does not beam the bass range. It takes a piano or something bigger to do so, but then it ain't clear to me where the sound is going, uprite piano versus concert piano, lid closed versus open. Tell me of one musical instrument, which is a strait dipole or cardioid with its radiation axis pointing to the listener.

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Old 23rd August 2017, 09:50 AM   #80
Juhazi is offline Juhazi  Finland
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Drums, cymbals, strings, harp come to my mind. But that is just theoretization and has nothing to do with sound reproduction at home. https://users.aalto.fi/~ktlokki/Publ..._aaua_2010.pdf


Summary






The sound radiation patterns of musical instruments represent a considerable part of the perceived room acoustics.


The directivities of fourteen common symphony orchestra instruments and a soprano singer during performance


are investigated. For this purpose, each instrument was recorded with the musician in an anechoic room with 22


microphones distributed around the player. As the result, directivities of the strings and woodwind instruments


are noticed to change with the played tone while the brass instruments radiate constantly in the direction of




the bell. Playing dynamics was not found to affect the directivity although the spectrum of the sound changes






considerably in particular with the brass instruments. The results can be utilized with source modeling in room


acoustics simulation and in research on musical acoustics.


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