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

[Archaea]

If you take away the resonance at 800 Hz, response is flat between 200 Hz and 10 kHz. That is very good considering the good directivity control.

@amirm, what's your take on that 800hz resonance not showing up with omnimic frequency response plots in room? As I mentioned in post 50 - I tested all 13 of my speakers from the same position and overlaid their FR to validate they were all the same. Before I shipped the new 70J-1 to you, I tested it against one of my existing speakers to make sure it had the same FR overlay and it did. My FR sweeps didn't catch a 800hz resonance, but I don't know if they should, or shouldn't have in the simple capture I did compared to your tool.

I freely admit I don't understand everything I read in this thread, and my knowledge level is basic compared to yours and some of the members here.
My FR capture/comparisons were only on axis, as pictured -- would that matter? I also measured, and use the speakers with no grills.

I'll put a snip of that picture set here for ease of view, but the uncompressed, more readable one is in post 50.

 

[MZKM]

@amirm, what's your take on that 800hz resonance not showing up with omnimic frequency response plots in room?

You have a bump in the response around the 800Hz resonance, your measurements probably has some smoothing so it doesn’t look as bad.

 

[Archaea]

You have a bump in the response around the 800Hz resonance, your measurements probably has some smoothing so it doesn’t look as bad.

more 950hz? the dark vertical line in the center is 1khz, but yeah okay I can see what you are pointing out. Left most side of graph frame is 100hz ,and it's 5 dB+ lower at 500hz (labeled) than it is at 950 hz in my capture.

1/12 smoothing was used on those captures (as seen in top right dropdown of omnimic software (easier to read in post 50)).

 

[MZKM]

more 950hz? the dark vertical line in the center is 1khz, but yeah okay I can see what you are pointing out. Left most side of graph frame is 100hz ,and it's 5 dB+ lower at 500hz (labeled) than it is at 950 hz in my capture.

1/12 smoothing was used on those captures (as seen in top right dropdown of omnimic software (easier to read in post 50)).

And 950Hz is around the peak in the Spin, and the rise starts around 600Hz, same with your measurement:

 

[Sancus]

The in-room measurement looks pretty much like the PIR to me. There is a ~5dB rise between 500hz and ~950hz in the omnimic graph, the PIR predicts ~4dB. The resonance is definitely there.

 

[Universal Cereal Bus]

Loosely speaking, the same basic beamforming theory as in these?

 

[MZKM]

This premium theater was setup with a full host of these JBL CBT 70j-1 speakers with the bass module 70je-1 mated to (brand new at the time) Dolby Atmos processing

I find it odd that Dolby doesn’t use specific speakers for all their theaters. The ones by me use dual horns (one facing towards the other end and one facing downwards):

 

[Archaea]

I find it odd that Dolby doesn’t use specific speakers for all their theaters. The ones by me use dual horns (one facing towards the other end and one facing downwards):

Kansas City is the headquarters for AMC. I was told they test new setups here, that do or don't make their way in more uniform cookie cutter fashion out to the other AMC theaters. Sadly the JBL's were replaced by some other flavor of speaker the next year or so in that same theater I originally heard them. The replacements were not nearly as good IMO, and were not CBTs or line arrays.

I wish I knew how they handled the surplus of equipment from their test theaters here. Wouldn't that be sweet!?!

Man - looking back at my original post about this - 2013. It's been that long? You can see some of the other KC AMC theater attendees comments in that thread on these JBLs. We all loved them!
https://www.avsforum.com/threads/am...s-reclining-electronic-leather-seats.1506209/

 

[Blumlein 88]

Tall panel ESL's share the line source nature of having only a 3 db/doubling drop off and reduced floor and ceiling reflections. However, they are usually wide enough they don't share the wide dispersion horizontally. So they don't have the same sound wherever you go in a room.

 

[rdenney]

These are PA speakers, and need to be understood in that context.

I installed a pair of the smaller CBT50’s at my church, driven by a Crown amp and a dbx Driverack PA2. The idea behind the CBT is to use a phased array to focus the sound into a horizontally plane, in the same way that a cluster of towers can be phased to aim or null AM broadcast signals in specific directions. With them mounted higher than the microphones, they will skip over the heads of the mikes and lay sound on the ears of the seated congregation.

The space the speakers face is 40x40’ with a 24’ ceiling plus a balcony, small by church standards but much bigger than a home.

Our church is live with lots of smooth decay. Bass isn’t important for voices, and musical instruments in that space don’t need or want amplification. These are used to reinforce voice, to punch through the reverberation for clarity, and they are stunningly good at that. Their efficiency and focus means I have the attenuators on the amp down to just above nothing, and I bought the smallest amp Crown makes. 20 clean watts would have been plenty. Nobody knows they are on except when they aren’t.

But with their pancake pattern, it might be a challenge to make them work at home.

JBL’s room software is very cool, and was extremely helpful to me.

The CBT-50’s are small and unobtrusive—perfect for a church PA.

I EQ’d them using the automated EQ procedure in the Driverack. I can crank this system to Voice if God levels and no hint of feedback. And that’s with the speakers mounted directly behind and three feet above the level of the microphones. We use Electrovoice condenser mikes and Shure wireless lapel mikes.

Rick “good response down to where the room takes over anyway—about 80 Hz” Denney

 

[Bartl007]

These are PA speakers, and need to be understood in that context.

I installed a pair of the smaller CBT50’s at my church, driven by a Crown amp and a dbx Driverack PA2. The idea behind the CBT is to use a phased array to focus the sound into a horizontally plane, in the same way that a cluster of towers can be phased to aim or null AM broadcast signals in specific directions. With them mounted higher than the microphones, they will skip over the heads of the mikes and lay sound on the ears of the seated congregation.

The space the speakers face is 40x40’ with a 24’ ceiling plus a balcony, small by church standards but much bigger than a home.

Our church is live with lots of smooth decay. Bass isn’t important for voices, and musical instruments in that space don’t need or want amplification. These are used to reinforce voice, to punch through the reverberation for clarity, and they are stunningly good at that. Their efficiency and focus means I have the attenuators on the amp down to just above nothing, and I bought the smallest amp Crown makes. 20 clean watts would have been plenty. Nobody knows they are on except when they aren’t.

But with their pancake pattern, it might be a challenge to make them work at home.

JBL’s room software is very cool, and was extremely helpful to me.

The CBT-50’s are small and unobtrusive—perfect for a church PA.

I EQ’d them using the automated EQ procedure in the Driverack. I can crank this system to Voice if God levels and no hint of feedback. And that’s with the speakers mounted directly behind and three feet above the level of the microphones. We use Electrovoice condenser mikes and Shure wireless lapel mikes.

Rick “good response down to where the room takes over anyway—about 80 Hz” Denney

For those that may question their fidelity, the CBT50 was used in a quasi domestic sized room at the CEDIA tradeshow JBL synthesis demo room (2015). I don't remember hearing any complaints about the "PA" speakers they were using for surrounds, but I will admit, I did not hear the demo for myself.

 

[Blumlein 88]

These are PA speakers, and need to be understood in that context.

I installed a pair of the smaller CBT50’s at my church, driven by a Crown amp and a dbx Driverack PA2. The idea behind the CBT is to use a phased array to focus the sound into a horizontally plane, in the same way that a cluster of towers can be phased to aim or null AM broadcast signals in specific directions. With them mounted higher than the microphones, they will skip over the heads of the mikes and lay sound on the ears of the seated congregation.

The space the speakers face is 40x40’ with a 24’ ceiling plus a balcony, small by church standards but much bigger than a home.

Our church is live with lots of smooth decay. Bass isn’t important for voices, and musical instruments in that space don’t need or want amplification. These are used to reinforce voice, to punch through the reverberation for clarity, and they are stunningly good at that. Their efficiency and focus means I have the attenuators on the amp down to just above nothing, and I bought the smallest amp Crown makes. 20 clean watts would have been plenty. Nobody knows they are on except when they aren’t.

But with their pancake pattern, it might be a challenge to make them work at home.

JBL’s room software is very cool, and was extremely helpful to me.

The CBT-50’s are small and unobtrusive—perfect for a church PA.

I EQ’d them using the automated EQ procedure in the Driverack. I can crank this system to Voice if God levels and no hint of feedback. And that’s with the speakers mounted directly behind and three feet above the level of the microphones. We use Electrovoice condenser mikes and Shure wireless lapel mikes.

Rick “good response down to where the room takes over anyway—about 80 Hz” Denney

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

Maybe good for surrounds, but I do prefer more low end from my surround speakers.

 

[amirm]

For those that may question their fidelity, the CBT50 was used in a quasi domestic sized room at the CEDIA tradeshow JBL synthesis demo room (2015). I don't remember hearing any complaints about the "PA" speakers they were using for surrounds, but I will admit, I did not hear the demo for myself.

I heard them and they were great. It was a massive theater with seating for some 20 to 30 people.

 

[Bjorn]

For those of you who want to read more about the CBT technology and see different presentations, you can use the link below.
https://www.keele-omholt-technologies.com/papers.php

We (K&O Tech.) plan to release a ground plane CBT to the home market hopefully before summer but progress are slow these days with the corona situation.

A difference between a CBT like the JBL 70J-1and a ground plane version is the latter avoids floor reflections as it uses the floor as an acoustic mirror of the speaker. The result of the avoidance of the floor reflections, minimization of ceiling reflections and minimization of the vertical room mode is much more even frequency response when placed in a living room.

 

[Biblob]

For those of you who want to read more about the CBT technology and see different presentations, you can use the link below.
https://www.keele-omholt-technologies.com/papers.php

We (K&O Tech.) plan to release a ground plane CBT to the home market hopefully before summer but progress are slow these days with the corona situation.

A difference between a CBT like the JBL 70J-1and a ground plane version is the latter avoids floor reflections as it uses the floor as an acoustic mirror of the speaker. The result of the avoidance of the floor reflections, minimization of ceiling reflections and minimization of the vertical room mode is much more even frequency response when placed in a living room.

Any snippets you can give us already on the new speaker?

 

[JustIntonation]

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.

This is somewhat surprising to me that you find it tonally correct since this speaker has no waveguide and a very wide horizontal directivity (only starts to slope in the top treble after you eq the resonance).
Usually when a speaker has a wide off-axis including treble you report that it sounds bright to you (and especially if that speaker also lacks bass like this one). Even speakers that have an objectively much higher score. But not this one apparently.
Perhaps it is not a 1dB/oct slope overall in room response but a narrow or sloping vertical off-axis which works for your listening situation / room?

 

[Bjorn]

Any snippets you can give us already on the new speaker?

I'll start a different thread at some point with more information. It doesn't belong in this one. Hopefully I can get Don Keele to share some as well.

Some pics below though.

 

[Bjorn]

This is somewhat surprising to me that you find it tonally correct since this speaker has no waveguide and a very wide horizontal directivity (only starts to slope in the top treble after you eq the resonance).
Usually when a speaker has a wide off-axis including treble you report that it sounds bright to you (and especially if that speaker also lacks bass like this one). Even speakers that have an objectively much higher score. But not this one apparently.
Perhaps it is not a 1dB/oct slope overall in room response but a narrow or sloping vertical off-axis which works for your listening situation / room?

It may be worth mentioning that the CBT only has a wide dispersion at a certain height. Above and below that window, the dispersion is actually narrow. The horizontal directivity of "traditional" CBT speakers will vary quite a bit and depends on the design.

I think many tend to disregard the importance and influence of vertical directivity. Floor and ceiling reflections arrive very early in most living rooms and don't add anything beneficial psycoacoustically. Especially the floor reflection is also almost impossible to treat in a linear way. A rug will alter the spectral content greatly and no one wants thick and huge absorbers on the floor. The vertical reflections causes quite strong tonal deviations.

It's possible to design a CBT with a narrow horizontal directivity. Or with the ability to change the horizontal beamwidth for that matter. Many possibilities but cost will substantially increase the more complex it's designed. Personally I lean towards horn speakers if a truly narrow directivity is desired. Because it can be done at a much lower cost. But it becomes big if it's going to be great sounding. No free lunch as they say.

 

[Jambo]

Approved by Aliens and H.R. Giger. It fits the decor perfectly.

 

[rdenney]

Hi Bjorn!

From the McIntosh website...

“The ported, 4-way XRT1.1K speaker uses our line array design to yield an even and wide sound field, producing exceptional stereo imaging in nearly all listening positions. With our line array speaker design, listeners closer to the XRT1.1K will not be overpowered by extremely high volumes as they will only be on axis to a portion of the drivers; listeners farther away will be on axis to more of the drivers and will be able to easily hear the music without any large drop off in sound level or quality.”

Those claims sound pretty CBT-like to me.

Btw, I have not heard them so just saying.

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