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

[Bartl007]

Thanks! Guessing that the CBT-70s could maybe be pushed a little bit more (80hz)?

-Jim

Don't forget the cbt50 is capable of 117dB peaks in music mode (111dB w/6dB Crest factor) and with only 3dB fall off for each doubling of distance from the speaker to your listening position, in most domestic spaces, these speakers have output to burn and are likely safe to boost some down low to get good integration with subs


As you can see, dirac thinks there is useful extension to ~60Hz in my room


The cbt50 should be capable of thx reference levels in all but the largest of home theaters in a surround application. Would really be a massive room to be further than 12ft(4m) from speaker to listener.


The cbt-70 is certainly more capable, but it's not exactly subtle mounted on your wall as a surround speaker. make sure to mock one up in cardboard to get a feel for how much room real estate you may be sacrificing with 4-6 of those mounted to your walls


Maybe someone can send one to Erin for testing since Amir doesn't think that output compression/distortion testing is important... Roll eyes

 

[jhaider]

Are you still happy with the CBT50s as surrounds? I'm very seriously considering buying four of them, to function as side and rear surrounds.

I'd be very interested in your (and others') opinion. For info: I sit approx 3 feet from my right surround, 4 ft from right surround back; 8ft from my left surround and 8 ft left surround back. I would need to mount the CBT50s flush to the wall using the flush wall mount. I find that, when using conventional speakers, the right side dominates significantly, even when all speakers are level-matched in Dirac.

Gimme a week or so and bug me if I haven't posted here yet. We recently had CBTs installed in our family room (50 for side, 100 for rear, the choice between the two in both cases being aesthetic) and there's a notable asymmetry to the side speaker depth. The left side has a fireplace that juts out. As a result the right CBT50 is mounted on the flush mount bracket (which BTW JBL's site is pretty misleading about: they only sell in pairs and come boxed as such but the price posted is per each) and the left CBT is on the standard bracket on the side of the fireplace wall, with the speaker normal to the bracket and the start of the baffle flush with the fireplace wall. (The rears are also on the flush brackets.)

I'm loathe to say anything yet because I haven't listened much (install finished Thursday) and they're not properly calibrated. Because of that I'm also currently running subless. (No subs is better than crappily integrated subs.) I just did a rough level match with the NIOSH app on my iPhone. That said, my initial impression is not "what the hell did I do?" but rather more positive than that. Hopefully there will be time to calibrate this weekend, but we'll see...

NB we're using the Crown DCIn amps for all channels. There is a "speaker tuning" for CBT50/100 but it only seems to include limiter. No PEQ.

 

[BenB]

Don't forget the cbt50 is capable of 117dB peaks in music mode (111dB w/6dB Crest factor) and with only 3dB fall off for each doubling of distance from the speaker to your listening position, in most domestic spaces, these speakers have output to burn and are likely safe to boost some down low to get good integration with subs

What is it going to take to kill this myth about line arrays having a drastically different fall-off in a domestic space?
The first thing to realize is that because of reflections, your typical speaker will exhibit only about a 3 dB fall-off with distance. To put it in perspective, when you move from 6 feet to 12 feet away from your speaker, you may have moved from 11.5 feet to 14.5 feet away from the virtual sidewall source.
The next thing to appreciate is that line arrays only exhibit a 3 dB fall-off in the nearfield. Those JBLs aren't that tall, and unless someone is using them as a monitor speaker on their desk, they are listened to in the farfield.
Lastly, to the extent that line array speakers reduce floor and ceiling reflections, they are reducing the reinforcement from those reflections that naturally reduces the fall-off with distance discussed in point 1 above.

I'm a huge fan of line arrays speakers, but it's because of the actual benefits of the speakers, and with few exceptions, a reduced fall-off rate isn't really one of them.

 

[Bartl007]

What is it going to take to kill this myth about line arrays having a drastically different fall-off in a domestic space?
The first thing to realize is that because of reflections, your typical speaker will exhibit only about a 3 dB fall-off with distance. To put it in perspective, when you move from 6 feet to 12 feet away from your speaker, you may have moved from 11.5 feet to 14.5 feet away from the virtual sidewall source.
The next thing to appreciate is that line arrays only exhibit a 3 dB fall-off in the nearfield. Those JBLs aren't that tall, and unless someone is using them as a monitor speaker on their desk, they are listened to in the farfield.
Lastly, to the extent that line array speakers reduce floor and ceiling reflections, they are reducing the reinforcement from those reflections that naturally reduces the fall-off with distance discussed in point 1 above.

I'm a huge fan of line arrays speakers, but it's because of the actual benefits of the speakers, and with few exceptions, a reduced fall-off rate isn't really one of them.

You are correct. I confirmed today with an SPL meter and tape measurer, that in my acoustically treated room, my cbt-50's fall off at 4-5dB per doubling of distance, the same as my direct radiating, two way LCR speakers.

Still these speakers can play plenty loud and can reach reference levels at my main listening position, even though I don't listen at that volume.

 

[BenB]

You are correct. I confirmed today with an SPL meter and tape measurer, that in my acoustically treated room, my cbt-50's fall off at 4-5dB per doubling of distance, the same as my direct radiating, two way LCR speakers.

Still these speakers can play plenty loud and can reach reference levels at my main listening position, even though I don't listen at that volume.

That's great that you were able to empirically test and compare the fall-off between a short line array, and a conventional 2-way speaker. Thanks for taking the time to do that. It's also nice when the empirical data aligns with the theory.

 

[Indy]

Why is there not more interest in these for lcr with a subwoofer? Posted this same question on another forum and a major poster said they don't equate to a horn system particularly Danley's. I'm thinking about getting some to test. I have a DIYSG horn system. I'd like to get some on walls to free up space.

 

[jdubs]

I’ve wondered the exact same. Seems like they would work well in that application.

Jim

 

[More Dynamics Please]

Why is there not more interest in these for lcr with a subwoofer? Posted this same question on another forum and a major poster said they don't equate to a horn system particularly Danley's. I'm thinking about getting some to test. I have a DIYSG horn system. I'd like to get some on walls to free up space.

FYI, JBL is advertising B-stock CBT 70J-1 for 30% off. Not sure what makes them B-stock but it does result in a savings of more than $300 per speaker.

JBL CBT 70J-1 (B-Stock) | Constant Beamwidth Technology™ Two-Way Line Array Column with Asymmetrical Vertical Cove

The CBT 70J-1, with Constant Beamwidth Technology™, represents a breakthrough in pattern control consistency, utilizing complex analog delay beam-forming and amplitude tapering to accomplish superior, consistent vertical coverage without the narrow vertical beaming and out-of-coverage lobing...

www.jbl.com

 

[AlexanderM]

My understanding is that B-stock means it was purchased and returned, then they checked it out, repaired it, and now it's good to go.

 

[jhaider]

Why is there not more interest in these for lcr with a subwoofer?

Because it’s hard to fit one as a center channel.

 

[Jonas_h]

Gimme a week or so and bug me if I haven't posted here yet. We recently had CBTs installed in our family room (50 for side, 100 for rear, the choice between the two in both cases being aesthetic) and there's a notable asymmetry to the side speaker depth. The left side has a fireplace that juts out. As a result the right CBT50 is mounted on the flush mount bracket (which BTW JBL's site is pretty misleading about: they only sell in pairs and come boxed as such but the price posted is per each) and the left CBT is on the standard bracket on the side of the fireplace wall, with the speaker normal to the bracket and the start of the baffle flush with the fireplace wall. (The rears are also on the flush brackets.)

I'm going to bug you since you haven't posted

How are your CBT-family room coming along? Are you happy with the result?

 

[Indy]

I would like to know how the cbt's are working in that room as well. I think I'll just oder a pair of the cbt 70 J-1 and try them for myself.

 

[jhaider]

I'm going to bug you since you haven't posted

With the caveat that I haven’t had any time to really listen closely, I’m satisfied with the CBT50 and CBT100 as, respectively, sides and rears. (JBL 708i LCR, TAD-Pioneer ceiling speakers placed and set as heights)

One thing is they’re pretty directional up top. Our rears fire straight out and Dirac “thinks” they roll off more than they perceptually do. I ended up curtaining Dirac on the top octave because of that.

 

[Dj7675]

With the caveat that I haven’t had any time to really listen closely, I’m satisfied with the CBT50 and CBT100 as, respectively, sides and rears. (JBL 708i LCR, TAD-Pioneer ceiling speakers placed and set as heights)

One thing is they’re pretty directional up top. Our rears fire straight out and Dirac “thinks” they roll off more than they perceptually do. I ended up curtaining Dirac on the top octave because of that.

Thinking of using one of the CBT models from JBL for surrounds or tops in our theater. What did you have to end up as the crossover for the CBT50/100?

 

[jhaider]

Thinking of using one of the CBT models from JBL for surrounds or tops in our theater. What did you have to end up as the crossover for the CBT50/100?

I'm pretty sure my crossovers are all between 100 and 120Hz. Likely closer to the latter. I never bought the idea that crossovers above 80Hz are localizable, caveat being we currently use three subs that on their own have smooth response a good 3 octaves or so above that.

While I think the CBT 50/100 form factor and dispersion are especially well suited for surround channels, I do not think they're a great fit for height speakers. They are not attractive if oriented correctly - you lose the slim unobtrusiveness if you mount high on front/rear walls, angled down to the LP, and end up with weird-looking thin sticks jutting out of the wall. The dispersion pattern is also IMO not well suited in terms of dispersion to an Atmos-type "tops" setup. (Maybe if you install them at 45 degree angles to the sidewalls? Then we get find ourselves deep in uggo-land though.) I know the famous CEDIA JBL Synthesis demo that put immersive (and the M2!) on the map for a lot of people used them as such, but JBL also used eleven CBT50's for the height layer in that setup.

 

[GimeDsp]

This is a review and detailed measurements of the special JBL CBT 70J-1 (upper unit) constant beam transducer design. It was kindly purchased new and shipped to me by a member. It costs US $1047 on Amazon including free delivery. You can get it in black or white colors.

Note: our company, Madrona Digital is a dealer for Harman and hence JBL. We have actually installed a number of these speakers in commercial applications. See: https://www.audiosciencereview.com/...ransducer-speakers-in-commercial-project.310/. You may also want to assign as much bias as you feel necessary for the subjective aspects of this review.

Other than being tall and narrow, little hints at the unusual design of this speaker:

View attachment 118768

There are four low frequency drivers and whopping 16 high frequency ones:
View attachment 118769

Using "shading control" the drivers work together to limit vertical dispersion to the height of the speaker.

There are two settings on the unit as you can barely see on the right bottom of the speaker above. One sets the width, I choose wide, and the other, "music or speech." I naturally selected music. JBL documentation shows these settings create the flattest response.

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise. Both of these factors enable testing in ordinary rooms yet results that can be more accurate than an anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.

I performed over 2000 measurement which resulted in error rate below 2% up to 10 kHz or so. Above that, error shoots way up so the response there is not correct. I could use more points but as is, it took nearly 5 hours to measure and created a 1.5 gigabyte measurement file!

Testing temperature was around 60 degrees F.

I could not see through the grill to pick a "reference axis" and wouldn't know where that would be anyway. So for measurements, I just picked a more or less center location on the flat part of the speaker.

Measurements are compliant with latest speaker research into what can predict the speaker preference and is standardized in CEA/CTA-2034 ANSI specifications. Likewise listening tests are performed per research that shows mono listening is much more revealing of differences between speakers than stereo or multichannel.

JBL CBT 70J-1 Measurements
Acoustic measurements can be grouped in a way that can be perceptually analyzed to determine how good a speaker is and how it can be used in a room. This so called spinorama shows us just about everything we need to know about the speaker with respect to tonality and some flaws:
View attachment 118771

Harman includes spin data that shows much flatter response than above. Specifically there is no sign of that resonance in their measurements. But it is in every aspect of my measurements. I even heard it during the sweep! The level went up and then back down in the middle. We can see evidence of resonance in waterfall display:

View attachment 118772

And evidence of even more of then in impedance and phase graph:
View attachment 118773

I could also see it in the 'in-room" distortion measurements:

View attachment 118774

Speaking of distortion, it is extremely low:
View attachment 118775

Sure, it doesn't attempt to play very low but what it does play is very clean.

Efficiency is the highest I have measured of any speaker I have tested, clocking at 92 dB or so.

Early window reflections are very good:
View attachment 118776

Notice how the ceiling reflections - dashed red - are at so much lower level due to beam forming produced by CBT technology. Floor reflections are not that much reduced though.

Our predicted in-room frequency response is very good, sans that resonance:

View attachment 118777

Horizontal directivity is wide and not controlled a lot:
View attachment 118778
View attachment 118779

Vertically, it is another game altogether:
View attachment 118780

This thing is a shaft of sound coming at you! Vertically directivity control is definitely there.

Edit: here are two 3D graphs which should help with understanding of how the sound field is shaped to be a horizontal donut as opposed to sphere:

View attachment 118970

View attachment 118971

Listening Tests
The efficiency advantage came through immediately as soon as I played my first track through the CBT J70-1. I could barely turn up the volume before the speaker would fill my large space with ease. Turn it up even more and it can get scary loud with no hint of distortion! Granted, deep bass is not there but everything above that plays with incredible efficiency and dynamics.

Tonality was very good but I thought I take down the resonance peak with EQ:
View attachment 118781

The difference was subtle. The sound was more open now, more detailed and slightly less harsh. Once there, I sat and listened and listened! It was an incredible experience.

If you have not ever heard a CBT speaker, it is something altogether different. You can walk up to it and level barely changes. Ditto for going back or even moving horizontally. It can almost be called "constant level speaker!" You feel like you are freed from sitting like a statute in a fixed spot. You can walk around a large area and overall response of the speaker barely changes. It is so uncanny and what I experienced when I listened to these at Harman years ago. They had them in this massive airplane hanger type building. Yet these were filling them with so little drop off in level as you walked forward and back.

While these speakers are a natural for outdoor use, they also make great surround speakers. They solve the issue of the people sitting to the sides hearing too much of the surround speaker closest to them.

Conclusions
I must say, while I expected to hear the nice experience of CBT beam forming, I did not expect the speaker to sound so correct tonally. And be so efficient and effort-free. With just that bit of EQ, you have a very high performance speaker. They need bass enforcement though. I have the companion lower half of this speaker which I will test next.

I am going to strongly recommend the JBL CBT 70J-1. You need to hear one to open your vista of what is possible with a bit of complex math.

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As always, questions, comments, recommendations, etc. are welcome.

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Hi Amir, I am looking at getting 2 of these or the 1000, did you mention what the vertical directivity switch was set to?

 

[Dj7675]

Hi Amir, I am looking at getting 2 of these or the 1000, did you mention what the vertical directivity switch was set to?

I believe it was set to Wide/Music

 

[More Dynamics Please]

One of the main criticisms of using LR speakers to create a phantom center is that it's only optimized for the center listening position and the center image isn't convincing when seated off center. Given the consistent audio characteristics of a CBT line array like the 70J-1 wouldn't it be more effective at creating a stable center image across multiple listening positions than more conventional LR speakers? If so then it could be a good option for a simple 2.1 or 2.2 system for music and non-surround movies with a pair of 70J-1s mounted on either side of a flat screen TV or non-AT projection screen where optimum center speaker positioning is not possible.

 

[beaRA]

One of the main criticisms of using LR speakers to create a phantom center is that it's only optimized for the center listening position and the center image isn't convincing when seated off center. Given the consistent audio characteristics of a CBT line array like the 70J-1 wouldn't it be more effective at creating a stable center image across multiple listening positions than more conventional LR speakers? If so then it could be a good option for a simple 2.1 or 2.2 system for music and non-surround movies with a pair of 70J-1s mounted on either side of a flat screen TV or non-AT projection screen where optimum center speaker positioning is not possible.

The wide dispersion helps mitigate the effect of level differences on the center image, but the precedence effect will still cause the image to move toward the nearest speaker. Another strategy to widen the phantom center sweet spot is to use narrow, constant directivity speakers with extreme toe-in. When you move to the side, the far speaker gets louder and the near speaker gets closer.

 

[JeanKazamer]

Would you guys attribute the low distortion to the multiple drivers used ?
Surely at this price range and with the number of drivers, those aren't probably " top " material .

Using more drivers to achieve the same SPL level means they have to work less and thus reduces distortion ??
( sounds logic to me if it is the case ... )