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JBL CBT 70J-1 Review (Constant Beam Transducer)

jhaider

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Those CBT 50s look like just the thing for a home theater center channel. 20 inches tall and 4 inches wide.

That’s the problem with them for fronts though. You can’t really lie them on their side.

If I were starting from scratch today I’d probably specify the longer version of that one (CBT100 I think) for sides and rears. If it didn’t make involve patching and cutting plaster/lath walls in very conspicuous places I might have changed things around here.
 

rdenney

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Pics of my CBT50 install, showing how small these are:
FE463E84-9BED-405B-9CC7-085E5A73B910.jpeg

C38F2798-FC72-467A-B367-26EF12BAC24B.jpeg


You’ll want to stand back a bit for the crop—iPhone pics are not for tight cropping, and the original pic covered the whole interior.

Rick “very unobtrusive, but very loud when needed” Denney
 

Rick Sykora

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Roger Russell, when he headed up speaker design for McIntosh, developed the line array concept. He wrote AES papers about it long before JBL’s CBT tech. But he did not phase the drivers for vertical directivity, and his design depends in floors and ceilings.

See here:

http://www.roger-russell.com/columns/columns.htm

His “current” IDS-25 is partly what motivated the Parts Express kit as I understand it.

Rick “probably repeated someone else” Denney

OT...

The XRTs may not be CBTs technically, but may be some "borrowing" of design practices to achieve some of the same benefits. ;)
 

MerlinGS

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OT...
The XRTs may not be CBTs technically, but may be some "borrowing" of design practices to achieve some of the same benefits. ;)
I am having a lot of trouble understanding why the XRTs (and the like) are being compared conceptually to CBT designs, it is not clear to me considering the design and concepts differ significantly. I understand both designs may have multiple drivers (although not necessarily; e.g. BG Radia RD75), but the approach to the designs and the size requirements are not similar. A common vertical line array, especially in the context of a home system, does not have to rely on a fixed arc with an amplitude shading of the drivers. The latter can make the speaker design a far more complicated endeavour. Also, it is the fixed arc and shading of drivers that allows CBTs to gain many of the advantages of conventional line array designs without its limitations. As some have already noted, a conventional line array needs to be nearly as tall as the ceiling to gain some of the benefits of line arrays. In contrast, a CBT design, can be much smaller and still achieve those benefits.

Thus far I have not seen any discussion of JBL's "faux" coaxial design. It reduces the size of the speaker (and may have other benefits), but I wonder if the frame that holds the tweeters is partly the source of the recorded resonance around 850Hz.
 

Bjorn

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A "coaxial" design like the JBL CBT will struggle with diffraction issues. You don't see a similar unevenness from a traditional CBT.
 

rdenney

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Read Russell's page. He talks about frequency-sensitive gain control away from center for line arrays that are not the full room height.

He also talks about gain multiplication and focusing.

But that does not mean that the CBT doesn't do anything new--it just means it builds on a body of development and other line arrays that build on that same development need not be a violation of JBL's patent. Russell had a few patents on the line array concept, too.

Rick "it's in there" Denney
 

Rick Sykora

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I am having a lot of trouble understanding why the XRTs (and the like) are being compared conceptually to CBT designs, it is not clear to me considering the design and concepts differ significantly. I understand both designs may have multiple drivers (although not necessarily; e.g. BG Radia RD75), but the approach to the designs and the size requirements are not similar. A common vertical line array, especially in the context of a home system, does not have to rely on a fixed arc with an amplitude shading of the drivers. The latter can make the speaker design a far more complicated endeavour. Also, it is the fixed arc and shading of drivers that allows CBTs to gain many of the advantages of conventional line array designs without its limitations. As some have already noted, a conventional line array needs to be nearly as tall as the ceiling to gain some of the benefits of line arrays. In contrast, a CBT design, can be much smaller and still achieve those benefits.

Thus far I have not seen any discussion of JBL's "faux" coaxial design. It reduces the size of the speaker (and may have other benefits), but I wonder if the frame that holds the tweeters is partly the source of the recorded resonance around 850Hz.

Yes, there is usually more than one way to solve a problem. ;) Most of the current CBT are only approximations of the desired shading, but are measurable and audible improvements.

Don Keele studied this and presented in an AES paper, but the easier read in this presentation: Microsoft PowerPoint - Keele - CBT Paper #6 Array Performance Ranking (DBK Version).ppt [Compatibility Mode] (audioartistry.com)
 
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Emlin

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The Kii BXT claims to do the line array thing up to 250Hz. I guess that that's useful, but exactly how useful?
 

Ilkless

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A CBT with Revel-level build and finishing, plus focus on FR smoothness would be killer. I think the rejuvenation it would bring to Harman's home audio lineup would outweigh the risk of fragmentation.
 

alanca3

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For comparison, this is the data from JBL's provided EASE file:
Distance: 50m
There are a lot of graphs available. If anyone wants to see more, let me know.

Balloon
lpSUjw7.gif



DI
s81r244.png



On Axis
cDw7oDq.png
 

Bjorn

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Yes, there is usually more than one way to solve a problem. ;) Most of the current CBT are only approximations of the desired shading, but are measurable and audible improvements.

Don Keele studied this and presented in an AES paper, but the easier read in this presentation: Microsoft PowerPoint - Keele - CBT Paper #6 Array Performance Ranking (DBK Version).ppt [Compatibility Mode] (audioartistry.com)
The presentation also shows that a circular or bent CBT is free lunch compared to a straight line array with delay from DSP/amps. The latter can achieve almost the same result, but brings up the cost considerably.

Personally I think the curved speaker also look much better, but I know other might feel differently.

IMG_1851.JPG
 

Spocko

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So here you have some amazing speaker technology from JBL that can be described as the "perfect" home theater surround speaker due to the constant amplitude of sound regardless of the seating distance. Why hasn't JBL explored this further for dedicated HT use?? It's like they have a gold mine of technology buried and no product manager to uncover the treasure that lays within.
 

Spocko

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The presentation also shows that a circular or bent CBT is free lunch compared to a straight line array with delay from DSP/amps. The latter can achieve almost the same result, but brings up the cost considerably.

Personally I think the curved speaker also look much better, but I know other might feel differently.

View attachment 119259
I am a HUGE FAN of these linear array speakers, if only JBL can dedicate their vast resources to make this happen.
 

test1223

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Hello,

a really interesting speaker. I am considering to buy a pair for stereo usage in a room where a perfect speaker placement isn't possible (asymmetrical placement in the room, a flat screen next to the speaker with almost no space between them, placed at a wall). The listening distance is about 3.2m (10.5ft) and the speaker distance is only 1.3m (4.3ft). With standard speaker the amount of direct sound at the listening position is to low, so a speaker with a narrow vertical directivity would definitely help a lot. Also the lower spl loss with distance should help from a theoretical stand point. I don't need the high spl capability at all. A good subwoofer and dsp will be added. 50% music and 50% movie usage.

I think a good linearray should outperform any standard speaker in this scenario.

It would be really nice if someone who has the speakers ( @Archaea ) can give me his thought. In general feedback is very welcome.

Best
Thomas
 

Archaea

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Hello,

a really interesting speaker. I am considering to buy a pair for stereo usage in a room where a perfect speaker placement isn't possible (asymmetrical placement in the room, a flat screen next to the speaker with almost no space between them, placed at a wall). The listening distance is about 3.2m (10.5ft) and the speaker distance is only 1.3m (4.3ft). With standard speaker the amount of direct sound at the listening position is to low, so a speaker with a narrow vertical directivity would definitely help a lot. Also the lower spl loss with distance should help from a theoretical stand point. I don't need the high spl capability at all. A good subwoofer and dsp will be added. 50% music and 50% movie usage.

I think a good linearray should outperform any standard speaker in this scenario.

It would be really nice if someone who has the speakers ( @Archaea ) can give me his thought. In general feedback is very welcome.

Best
Thomas
Could you take a picture of the space? My pea brain is having trouble imagining the scenario where your listening position is 10’ but the speaker would be 4’ and a traditional speaker direct sound output would be too low? I already committed to a learning and subjective test requested by another member to place the two speakers horizontal and try to describe the imaging and dispersion/reflection differences between vertical placement and horizontal placement for stereo listening. While the speakers are out of my baffle wall I will test your scenario and also give you a subjective evaluation - but it will help me to see it.
 

test1223

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Could you take a picture of the space? My pea brain is having trouble imagining the scenario where your listening position is 10’ but the speaker would be 4’ and a traditional speaker direct sound output would be too low? I already committed to a learning and subjective test requested by another member to place the two speakers horizontal and try to describe the imaging and dispersion/reflection differences between vertical placement and horizontal placement for stereo listening. While the speakers are out of my baffle wall I will test your scenario and also give you a subjective evaluation - but it will help me to see it.
roomDG.jpg


Yes I have tested and designed many speakers and set-ups and the amount of direct sound should be in the range of a studio set-up (EBU listening recommendations). You can achieve this with standard big or PA like speakers (12 1), but you have the disadvantage of no envelopment, so a more narrow vertical and wider horizontal dispersion should be a lot better.
The speakers will be placed beside the TV with no distance to the wall and TV and will be tilted a bit upwards to also cover the upper part of the room which will hopefully provide more diffuse later reflections than a standard narrow di box.

The mini JBL 104 are there only to get some sound but they are not good at all for this purpose.

Thank you very much for helping me out.
 

Bjorn

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With a room like that I would have personally chosen speakers with super narrow horizontal dispersion (preferably narrow vertically too) and treated the rear wall with absorption behind the head.
 

test1223

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With a room like that I would have personally chosen speakers with super narrow horizontal dispersion (preferably narrow vertically too) and treated the rear wall with absorption behind the head.
Yes that is plan B. The main disadvantage is that you have almost no envelopment. This can only be solved with some additional "ambiance" speakers and I don't want to design a speaker for this room... Also all speakers which are good, provide such a di and are not super expensive are big. The space is very limited and is not appealing from the optics. If you have some suggestions I will be very happy.

Damping of the rear wall is an option but with such a none optimal configuration I thing it is more a wast of aesthetics for not much better sound.
 
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