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

[Rick Sykora]

Without derailing the thread too far, do you mind if I ask you which BG ribbons and in what configuration? And to bring it back to the thread, sonically how did they differ and resemble the CBTs? Thanks

Will PM you later as this is off-topic.

 

[HammerSandwich]

Just to keep them out harm's way, my ground plane CBTs are placed against a back wall (as far as the arc allows) and sound just as good as if placed further out in the room.

What's the wall surface above the array? Any damping?

 

[Rick Sykora]

What's the wall surface above the array? Any damping?

If you are asking about room treatment, did not need. Have 8 ft ceilings and carpeted floors, a set of leather sectionals and cloth curtains. The room leans toward be less lively than more. Hope this helps!

 

[Selah Audio]

Some bigger CBTs in churches.
View attachment 119108

View attachment 119110

I spent many hours helping build those arrays!

 

[Selah Audio]

I don't see how a ground plane CBT would make any sense in most domestic rooms. The backward radiation onto the front wall would cause a very strong reflection. I recall reading about an installation where the owner ended up using multiple FEET of absorption on his front wall to try to mitigate it. I remember thinking how unfair it was that Don put together a white paper comparing his design to a B&W speaker. He had them both in a very large warehouse, and blasted the B&W for the uneven impact of the floor reflection on the measurements at the listening position. He didn't have any wall behind the speakers, that would cause similar issues for his speaker.

Actually it wasn't a large warehouse and I helped him do the measurements for that AES paper. Yes, Don is biased - which is not unusual based on the other loudspeaker engineers I've met over the years.

 

[Selah Audio]

Narrow baffles combined with small drivers that don't beam until high in frequency is a recipe for a lot of sound wrapping around the baffle and radiating backward. Secondly, by effectively eliminating a floor bounce, and reducing the ceiling reflections, the reflection off the front wall becomes a higher fraction of the sound reaching the listener. Third, to whatever extent the speaker "defies the inverse square law", the sound from the virtual source behind the wall is louder at the listening position than a traditional speaker that does follow the inverse square law. Lastly, these types of speaker are advertised as being "room friendly" and mitigating undesirable early reflections, so the customer base is skewed toward those who care about reducing unwanted early reflections.

I've stood behind several CBT arrays of different sizes and found no problems; in fact, in some cases even less rear radiation than what you might expect from a conventional speaker.

 

[Selah Audio]

 

[Bjorn]

Do you have measurements to show the difference at the listening position?

I can show measurements of the CBT36 with different positions if you'd like. Let me know which measurements you want to see, and I'll post them in the thread below since it's off-topic here.
https://www.audiosciencereview.com/...th-transducer-cbt-speakers.12060/#post-351081

 

[Selah Audio]

I've worked with Don Keele on CBT arrays and posted some of the work in a few pictures above. We've also discussed the implementation of the technology by JBL / Harman. This particular JBL design doesn't really fully exploit the intended purpose of the CBT concept. The very narrow vertical coverage is the result of a shorter array with a minimal arc angle. Here's a picture of an array that I designed that uses a 40 degree arc and has very good vertical coverage. I cannot take credit for the cabinet though; in fact, we had a company in the EU trying to copy what was done by the DIY builder, Kevin Kendrick.

 

[yourmando]

I've worked with Don Keele on CBT arrays and posted some of the work in a few pictures above. We've also discussed the implementation of the technology by JBL / Harman. This particular JBL design doesn't really fully exploit the intended purpose of the CBT concept. The very narrow vertical coverage is the result of a shorter array with a minimal arc angle. Here's a picture of an array that I designed that uses a 40 degree arc and has very good vertical coverage. I cannot take credit for the cabinet though; in fact, we had a company in the EU trying to copy what was done by the DIY builder, Kevin Kendrick.

Doug Button’s JBL CBTs use shading (attenuation) and delay to create the same effect as the arc but in a physically straight form factor.

A big benefit is you still get the CBT behavior, but in a more flexible form factor allowing for many more mounting options, such as flush mounting on a wall, or angling down from high on down fill applications.

(The 70J and 1000 do have a j taper at the bottom, but the back remains flush)

Another benefit of doing the “arc” this way is that it is configurable to allow for different fill patterns.

The 70J has “broad” and “narrow” vertical fill patterns to tune for long vs shorter throw applications. And the JBL polar plots show the “broad” settting avoiding the lobing at higher frequency that “narrow” has.

The latest JBL CBT 1000 has multiple fill setting settings for each the top and bottom sections independently!

Finally, they have a CBT software tool that allows you to model the location and angle of the speaker, the depth and rise of the room, the mic/seating positions, etc. or multiple planes like a lower and balcony area. So you can see which placement and fill settings work best to cover the listening area more evenly.

The physical arc designs are great for those that can accommodate that shape, but the JBL form factor and configurable options allows for many many more applications, such as using them as surrounds. They are also relatively inexpensive!

 

[yourmando]

@amirm or @Archaea , do the 70J have any audible hiss at normal listening distances? It is a very high efficiency speaker.

Also, what amplifiers to you use, @Archaea ? I know there are Crown CDI models with built in DSP tunings for the 70J and other JBL speakers. Some say these amps cause too much hiss for the M2, which also has 92db efficiency I believe, so they use other amps the the Benchmark Media.

 

[Pultzar]

What do people think about the CBT 1000 for domestic use?

 

[yourmando]

What do people think about the CBT 1000 for domestic use?

I think the idea of the CBT 1000 is very intriguing for home use.

I’ve been researching it and I can think of multiple good uses for the new “country” home I just bought:

1. Garage/workshop/workout space.
2. Outdoors / garden use. Can be mounted far out on a pole, or flush mounted on an outside wall pointed toward the garden area. (Thankfully, no neighbors nearby to annoy.) These are also outdoor rated.
3. Dedicated home theater use as LCRs behind an acoustically transparent screen to go with 70Js as the surrounds. The full stack of CBT 1000 plus its own bass module brings the total CBT heigh to nearly 7 feet and controls vertical directivity down to 200 hz for +/- 20 degrees, and still good control below that. That is pretty amazing. (I know these won’t measure as perfectly as stuff like the M2s, but the directivity control looks excellent and therefore very EQable, and would extend the “constant level” trick to all speakers. Ideally I would be able to audition these vs M2s as LCR but that is unlikely to happen.)

All of these are uses stated in the JBL literature.

Finally, the independent pattern control feature for both the up and down directions can optimize each of these usage scenarios.

For example, these could be mounted higher in the workout room with the downfill pattern on, and the up full pattern more straight ahead.

The garden one could have more of a long throw pattern unless you want a super high pole.

The dedicated theater would probably have 1 our 2 risers so the upfill pattern could accommodate the rising seating slope. The full height 2 module stack cover seats up close and people standing in the back.

 

[Archaea]

@amirm or @Archaea , do the 70J have any audible hiss at normal listening distances? It is a very high efficiency speaker.

Also, what amplifiers to you use, @Archaea ? I know there are Crown CDI models with built in DSP tunings for the 70J and other JBL speakers. Some say these amps cause too much hiss for the M2, which also has 92db efficiency I believe, so they use other amps the the Benchmark Media.

I use my Denon AVR x6700h to power six speakers and my Sherbourn PA 7-350 to power 7 speakers. Neither make enough noise to be audible from the seats (once the AVR power has stabilized) To hear any hiss I'd have to walk right up to the speaker and stand with my ear immediately next to the drivers, even then it's VERY slight. This has not proved a problem whatsoever in my room with these speakers. (Aside from the startup/warmup noise on my Denon x6700wa which goes away after a couple minutes of power on — I suspect it’s related to the Denon capacitor issue that Amirm caught on his first x6700h review)

I have tried it with three different AVRs /pre-pros. No problem with any of them in tandem with the JBL 70J-1 in use.

I do have my main speaker amp and AVR both running through a Panamax M5400PM line conditioner - for what that's worth.

Denon x7200wa avr
Denon x6700h avr
Onkyo 5508 pre-pro

 

[Rick Sykora]

@richard12511 (and anyone else who may be interested)...

Late last year, Dr. Toole gave his opinion about dipoles on the thread about omnidirectional speakers. When I asked a followup about CBTs, he did not offer an opinion. Granted his book did give them some kudos (as surrounds). If he had any non-negative opinion to offer on using them as mains, he has had multiple opportunities to express his opinion.

Given his published work and the fact that he does not use CBTs in his home theater, is pretty evident he did not consider CBTs superior enough to endorse or utilize them. If he has them tucked away in a private listening room, I would be shocked. Little doubt he has had ample access to the JBL CBT products.

That said, while respecting his contributions to the study of audio, am hopeful that there is something beyond monopoles in our future. Even with fancy processing, multiple monopoles do not come close to the sound stage I have heard from my modest CBTs for home theater listening. Btw, I do have a private listening room and it is currently monopoles. Am looking forward to upgrading them to the next best speaker design (that is affordable and can pass SAF!).

 

[Selah Audio]

So Harman have been fudging their spin data and FR.

It could be due to smoothing and / or the measurement distance.

 

[Selah Audio]

Way cool man. How much SPL loss can be expected in such designs with doubling of distance?

It depends on the distance where you measure from. It will transition from 3dB to 6dB when you move away from the nearfield. With this being a shorter array measurements at increasing distances are important.

 

[Selah Audio]

Doug Button’s JBL CBTs use shading (attenuation) and delay to create the same effect as the arc but in a physically straight form factor.

A big benefit is you still get the CBT behavior, but in a more flexible form factor allowing for many more mounting options, such as flush mounting on a wall, or angling down from high on down fill applications.

(The 70J and 1000 do have a j taper at the bottom, but the back remains flush)

Another benefit of doing the “arc” this way is that it is configurable to allow for different fill patterns.

The 70J has “broad” and “narrow” vertical fill patterns to tune for long vs shorter throw applications. And the JBL polar plots show the “broad” settting avoiding the lobing at higher frequency that “narrow” has.

The latest JBL CBT 1000 has multiple fill setting settings for each the top and bottom sections independently!

Finally, they have a CBT software tool that allows you to model the location and angle of the speaker, the depth and rise of the room, the mic/seating positions, etc. or multiple planes like a lower and balcony area. So you can see which placement and fill settings work best to cover the listening area more evenly.

The physical arc designs are great for those that can accommodate that shape, but the JBL form factor and configurable options allows for many many more applications, such as using them as surrounds. They are also relatively inexpensive!

Yes, I am aware of the shading and the novel use of passive filter delays to help shape the beamwidth. I helped build the arrays in the attached picture, which I believe were the first large scale CBT arrays in the USA. It would be helpful to see how these measure at different distances in a home setting.

 

[yourmando]

I use my Denon AVR x6700h to power six speakers and my Sherbourn PA 7-350 to power 7 speakers. Neither make enough noise to be audible from the seats (once the AVR power has stabilized) To hear any hiss I'd have to walk right up to the speaker and stand with my ear immediately next to the drivers, even then it's VERY slight. This has not proved a problem whatsoever in my room with these speakers. (Aside from the startup/warmup noise on my Denon x6700wa which goes away after a couple minutes of power on — I suspect it’s related to the Denon capacitor issue that Amirm caught on his first x6700h review)

I have tried it with three different AVRs /pre-pros. No problem with any of them in tandem with the JBL 70J-1 in use.

I do have my main speaker amp and AVR both running through a Panamax M5400PM line conditioner - for what that's worth.

Denon x7200wa avr
Denon x6700h avr
Onkyo 5508 pre-pro

Excellent, thanks!

 

[yourmando]

Late last year, Dr. Toole gave his opinion about dipoles on the thread about omnidirectional speakers. When I asked a followup about CBTs, he did not offer an opinion. Granted his book did give them some kudos (as surrounds). If he had any non-negative opinion to offer on using them as mains, he has had multiple opportunities to express his opinion.

Given his published work and the fact that he does not use CBTs in his home theater, is pretty evident he did not consider CBTs superior enough to endorse or utilize them. If he has them tucked away in a private listening room, I would be shocked. Little doubt he has had ample access to the JBL CBT products.

I don’t think many would claim the CBTs are superior in every home theater use, or that there are no good CBT theater applications.

Floyd Toole wrote a fascinating article on his home surround setup:

https://www.thescreeningroomav.com/...te-real-world-home-theater-and-listening-room

A system based on Salon2s, Gem2, Voice2 etc are clearly an ultimate setup.

He also had specific needs. For example he wanted this for a multi use room that looked “relatively normal” vs a dedicated escape room (where he could hide M2 and Synthesis speakers, maybe).

Let’s face it, the Salon2s look much better in such a room, and he has the means made maybe special access to get the “ultimate.”

Perhaps he would consider CBTs as surrounds if he had a dedicated space and wanted a much wider listening area, as he mentioned in his book. Or maybe he’s not into that and only wants the best speakers for a couple “money seats,” but might feel differently in a public cinema he’s attending so he can get even levels no matter where he’s sitting.

It doesn’t seem like CBTs are the ultimate for everything, but do have unique strengths for a number of applications.