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

[Archaea]

@Wright Sound
Yep. These turkeys sure are terrible…

And

I originally heard them in an AMC Prime theater that would seat probably ~250 people and they were the best sounding cinema speaker / best commercial theater experience I’d ever heard. (Which is why I bought them myself.)
So perhaps the churches you heard them in didn’t have them setup correctly? Have you measured them yourself? Or auditioned a pair under your own setup control?

 

[Bjorn]

There is no magic going on here. And I can tell you, based on actually seeing (and hearing) these turkeys in 2 different churches, they are remarkably ineffective. Short throw, inefficient, very beamy on the highs, disregarding the useless lack of bass. The real problem is that they are being marketed for churches and auditoriums, but have neither the directivity, pattern control, projection, or efficiency for those jobs. 93dB is not high efficiency. A typical pro speaker is 100dB or more sensitivity; a 7dB difference equals 5 times the power, so figure that out for yourself.
While they might be adequate for a conference room, or maybe your jazz trio at the coffee house, there’s much cheaper ways to do that. To reach the back of a room 60’ to 100’ long, requires long throw speakers with a narrow dispersion, like 40°, not a bunch of 1” tweeters. And the data AMIRM posted shows that JBL was lying, or at least misleading about the highly touted "constant beamwidth". Bottom line - they are not only inadequate, they are totally the wrong design for a sound system in a church or auditorium. Note: JBL's own guide suggests that more speakers might (probably) need to be added for coverage. Well ….. if I spend over a thousand dollars on a speaker, I certainly expect it to cover the whole room.
See photos of my designs that actually work.
P.S. Don’t get hung up on the slight advantage of cylindrical vs spherical, No loudspeaker radiates a spherical wave. A 12” or 15” speaker is about 90° conical. A horn will give a 20dB - 30dB advantage of loss per distance, not a mere 3dB. This is another topic fully worthy of a detailed discussion. Very many people have misunderstood this for a long time. Check these out for the 411: http://www.csgnetwork.com/speakerqestcalc.html http://www.mcsquared.com/Qcalc.htm

Together with the bass unit, which also extends the vertical directivity lower in frequency, they work well for smaller churches or churches where the speakers are only used for speech. For very large venues and especially when used for music, you need something else. For instance a CBT speaker you see below.

They are not very beamy in the highs. They get narrower as we can see from horizontal polar below, but still fairly wide in the highs. A typical waveguide/horn speaker will be narrower.

The vertical directivity is actually around 40°, which you say is ideal. However, you need more drivers to reach the back in a very large venue. The vertical polar below shows around 20° up and down, which is a beamwidth of 40°.

The speakers you are showing pictures of are speaker designs with a typical collapsing polar and with serious vertical lobing and comb filtering. Something the CBT design avoids. The weaknesses with the JBL CBTs is primarily how they have placed the drivers, which leads to diffraction, and the fact that they aren't using very many drivers. A taller unit with more drivers has several benefits. And in a domestic room, the ground plane CBT is a much better option as front speakers. Also in some large venues, a ground plane version would be a better choice.

 

[Archaea]

A video of the JBL CBT 70j-1 off axis, at distance, and showing FR with real time analysis.

 

[williamwally]

Those cbt's really seem to perform in room.

However there's definitely not enough subs in that room.

 

[Bjorn]

This is why it's called constant beamwidt transducer.
Also check out Don Keele's real time measurement of the CBT36 and how it compares to a 3-way speaker.

 

[Archaea]

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.

I tested this tonight. Reduced SPL fall off at distance seems pretty legit to me. 3.7dB more SPL in my farthest seat as compared to a traditional 3 way bookshelf design. See my testing here.
NO EQ on the AVR, no subs turned on, and AVR was in direct mode with my AVR crossover set to 250hz. (The highest it could be). Denon x6700h AVR. The right channel was feeding my right surround through my amp and the left channel unplugged.

 

[Randy Bessinger]

^^Nice work Archaea!

 

[lewdish]

I went to an AMC Prime the other night to see Guardians of the Galaxy Vol. 3, hoping to hear the JBL CBT setup there, but the model I saw there doesn't seem to be the same CBT series that Amir reviewed. I also couldnt find this model on JBL's site either. Anyone able to identify? It does have that kinda curved CBT look to it but the arrays were quite short

 

[TomG]

Hi all, I recently came in contact with this speaker while stopping in a local church. My wife and I were sitting in the third row from the stage. Once the music started , holy cow!! why is it so loud ? I look up and mounted directly above the pulpit, aiming down the center of the church , CBT 70J ! like a sword of a HF sound beam !. I check the db meter in my phone, peaks of 94DB!!!!!! to make it even better, bare walls, plenty of glass, can you say clap echo ? wow. I don't know how they had the controls set. The Pastor told me he sent the measurements into sweet water, and they recommended the system. They spent quite a few bucks, (saw some big subs, all jbl system). I advised him in the nicest way I could, they are damaging peoples hearing. Any advice on set up for these things? funny,mit sounded good on the boarders of the room, away from the beam!(death ray lol). Thanks for any feed back, Tom G

 

[Rick Sykora]

Hi all, I recently came in contact with this speaker while stopping in a local church. My wife and I were sitting in the third row from the stage. Once the music started , holy cow!! why is it so loud ? I look up and mounted directly above the pulpit, aiming down the center of the church , CBT 70J ! like a sword of a HF sound beam !. I check the db meter in my phone, peaks of 94DB!!!!!! to make it even better, bare walls, plenty of glass, can you say clap echo ? wow. I don't know how they had the controls set. The Pastor told me he sent the measurements into sweet water, and they recommended the system. They spent quite a few bucks, (saw some big subs, all jbl system). I advised him in the nicest way I could, they are damaging peoples hearing. Any advice on set up for these things? funny,mit sounded good on the boarders of the room, away from the beam!(death ray lol). Thanks for any feed back, Tom G

maybe you could work with sweetwater to reconfigure the software?

if not, may be they could recommend someone to do. you can also find local audio engineers on AES site if needed.

 

[dasdoing]

Hi all, I recently came in contact with this speaker while stopping in a local church. My wife and I were sitting in the third row from the stage. Once the music started , holy cow!! why is it so loud ? I look up and mounted directly above the pulpit, aiming down the center of the church , CBT 70J ! like a sword of a HF sound beam !. I check the db meter in my phone, peaks of 94DB!!!!!! to make it even better, bare walls, plenty of glass, can you say clap echo ? wow. I don't know how they had the controls set. The Pastor told me he sent the measurements into sweet water, and they recommended the system. They spent quite a few bucks, (saw some big subs, all jbl system). I advised him in the nicest way I could, they are damaging peoples hearing. Any advice on set up for these things? funny,mit sounded good on the boarders of the room, away from the beam!(death ray lol). Thanks for any feed back, Tom G

sounds like they were in narrow mode? in the described setup they need to be in wide (unless they are used one on top of the other). the narrow settings also has a boost in the treble.

 

[TomG]

sounds like they were in narrow mode? in the described setup they need to be in wide (unless they are used one on top of the other). the narrow settings also has a boost in the treble.

Thanks much, I plan to go back there and advise them. I'll check their settings, if they let me.I just walked in and told them they have a problem, while I was talking some one else came over and had the same complaint, so maybe they will be open to suggestions. Also, any idea how high up these should be ? thanks again. TG

 

[TomG]

maybe you could work with sweetwater to reconfigure the software?

if not, may be they could recommend someone to do. you can also find local audio engineers on AES site if needed.

Thanks, good idea's. Like I said , I was just a visitor to the church . I plan to go back just to see if I could be of help. It really was way too loud, hearing damage loud ! if they want I would talk to sweet water for them to describe the problem. funny, even after this I wouldn't mind a pair to play with ! they throw some sound, that's for sure. Anyway, thank you gentlemen. TG

 

[TomG]

I willed you know what happens when I go back, thanks again. Tom G

 

[rdenney]

Hi all, I recently came in contact with this speaker while stopping in a local church. My wife and I were sitting in the third row from the stage. Once the music started , holy cow!! why is it so loud ? I look up and mounted directly above the pulpit, aiming down the center of the church , CBT 70J ! like a sword of a HF sound beam !. I check the db meter in my phone, peaks of 94DB!!!!!! to make it even better, bare walls, plenty of glass, can you say clap echo ? wow. I don't know how they had the controls set. The Pastor told me he sent the measurements into sweet water, and they recommended the system. They spent quite a few bucks, (saw some big subs, all jbl system). I advised him in the nicest way I could, they are damaging peoples hearing. Any advice on set up for these things? funny,mit sounded good on the boarders of the room, away from the beam!(death ray lol). Thanks for any feed back, Tom G

In the system I built, I have the Crown amplifier attenuated down to probably five watts. All it does is put a point on the consonants so that they don't blur in the reverberation of the room. Clarity is greatly improved but people generally don't perceive that a sound system is being used.

Rick "that's why it's called sound reinforcement" Denney

 

[MediumRare]

Thanks, good idea's. Like I said , I was just a visitor to the church . I plan to go back just to see if I could be of help. It really was way too loud, hearing damage loud ! if they want I would talk to sweet water for them to describe the problem. funny, even after this I wouldn't mind a pair to play with ! they throw some sound, that's for sure. Anyway, thank you gentlemen. TG

Perhaps you can offer to run an REW sweep with the mic in a few different locations. That would immediately determine what changes need to be made.

 

[dasdoing]

Thanks much, I plan to go back there and advise them. I'll check their settings, if they let me.I just walked in and told them they have a problem, while I was talking some one else came over and had the same complaint, so maybe they will be open to suggestions. Also, any idea how high up these should be ? thanks again. TG

I wonder, they invested in a good system....so who set it up?
there is software to find the best position for them. that's what the Ease and CLF files in the download section are for.
if these are the only mains, the higher the better for uniform loudness.
fiering in the middle of the audience is a good starting point, though looking at the vertical they probably should better aim at the last 3rd of the audience. that should also even out the treble since there will be loss over distance. but it depends on how big the audience space is, the first row obviously should be in that 45 degrees angle.
But again, this should be simulated in software.

EDIT: these have actually their own specialized software: https://jblpro.com/en/softwares/cbt-calculator-v1-3-0-1

 

[rdenney]

I used JBL's software for location for the CB50's I installed at our church. For these, "higher is better" is not necessarily the case. These put out a flat pattern with attenuation above and below the plane extending out from the speakers. Horizontally, they are wide, but vertically they are narrow. I wanted that plane to float over the top of the lectern and pulpit microphones and hit the middle and back of the audience more than 15 feet back from the front of the seating area. Within 15 feet, the consonants could be heard clearly without sound reinforcement, but they blurred farther back due to reverberation. But I also wanted some effect of the speakers in the balcony. Mounting them too high would have forced a different type of loudspeaker array with more vertical spread.

And there is the issue of maintaining speakers hanging from a 24-foot ceiling. I only needed an 8-foot ladder to reach my mounting points.

As with all technical projects, understanding the objectives is the critical first step. Is it a dead room that needs everything amplified to be heard? Is it a live room that smears speech acoustically but it's plenty loud without amplification? If the former, the objective would be to create a reasonable facsimile of the speaker's voice with the impression that it is coming from the person speaking. That needs an array above the speaking point with a fairly wide pattern so that everyone hears the same basic amplification. But if it's the latter (and being too live describes most traditional church architecture), then speakers need a narrow pattern and need to be positioned to put those consonants at the people who aren't getting them acoustically.

For equalization, I used a dbx PA2 parametric equalizer with its calibrated microphone to balance sound and (mostly) to notch out resonant frequencies to attenuate feedback.

But there is also the PAF (preacher acceptance factor). Some preachers believe their voices to be able to carry to the crowd of 5000 for the Sermon on the Mount. They hate amplification because they think it is unrealistic. Others want just the opposite, because they view themselves as giving a stage performance, and want every whisper to pin people to their seats. And don't even get me started on the choir, which thankfully is happy without amplification at my church.

Rick "better to discuss objectives with those who have them than argue about design with amateurs" Denney

 

[dasdoing]

I used JBL's software for location for the CB50's I installed at our church. For these, "higher is better" is not necessarily the case. These put out a flat pattern with attenuation above and below the plane extending out from the speakers. Horizontally, they are wide, but vertically they are narrow. I wanted that plane to float over the top of the lectern and pulpit microphones and hit the middle and back of the audience more than 15 feet back from the front of the seating area. Within 15 feet, the consonants could be heard clearly without sound reinforcement, but they blurred farther back due to reverberation. But I also wanted some effect of the speakers in the balcony. Mounting them too high would have forced a different type of loudspeaker array with more vertical spread.

And there is the issue of maintaining speakers hanging from a 24-foot ceiling. I only needed an 8-foot ladder to reach my mounting points.

As with all technical projects, understanding the objectives is the critical first step. Is it a dead room that needs everything amplified to be heard? Is it a live room that smears speech acoustically but it's plenty loud without amplification? If the former, the objective would be to create a reasonable facsimile of the speaker's voice with the impression that it is coming from the person speaking. That needs an array above the speaking point with a fairly wide pattern so that everyone hears the same basic amplification. But if it's the latter (and being too live describes most traditional church architecture), then speakers need a narrow pattern and need to be positioned to put those consonants at the people who aren't getting them acoustically.

For equalization, I used a dbx PA2 parametric equalizer with its calibrated microphone to balance sound and (mostly) to notch out resonant frequencies to attenuate feedback.

But there is also the PAF (preacher acceptance factor). Some preachers believe their voices to be able to carry to the crowd of 5000 for the Sermon on the Mount. They hate amplification because they think it is unrealistic. Others want just the opposite, because they view themselves as giving a stage performance, and want every whisper to pin people to their seats. And don't even get me started on the choir, which thankfully is happy without amplification at my church.

Rick "better to discuss objectives with those who have them than argue about design with amateurs" Denney

very interesting. I didn't even think about how the first church rows don't necessarily need reinforcement.

 

[rdenney]

very interesting. I didn't even think about how the first church rows don't necessarily need reinforcement.

Yeah, the issue is the relationship between direct acoustic sound and reflected/reverberant sound. The further back in the room one goes, the higher the percentage of reverberant sound. One reason I went with the CBT50 model is that it drops off considerably below 100 Hz, which is where the room needs attenuation more than amplification. Attenuation was not an option, and while being desirable for speech intelligibility it undesirable for live music. So, there was no interest in putting up absorbent panels. Echo isn't that bad, mostly because the ceiling is curved rather than flat. But there is a lot of reverberation--the RTA60 is several seconds.

So, really what I wanted was amplification in the speech range and higher for the middle and back of the room. Consonants produce impulses with high overtones (just like a click) and that's what I wanted to emphasize. Nobody realizes the system is on until it isn't.

Some designers will place speakers along the sides to provide that amplification in the middle and back, but then are faced with localization problems. At the very least, they need enough of a time delay to sound like a reflection rather than getting in front of the primary sound. That becomes much more complicated and expensive, though if our church was much larger and long for its width, as are a lot of traditional cathedral architectures, it might be necessary. Our seating area is nearly square, plus a balcony further back and (obviously) higher.

I also installed a hearing-aid loop system, which transmits a base-band audio electromagnetic field in the room. Hearing aids with "t-coils" will be excited by the signal in that base-band em field. It's like radio but without being modulated onto an RF carrier frequency. But I didn't want speech-only EQ on that system--that signal needed to be full-range. So, I bought the speakers for their natural emphasis in the speech band so I didn't have to do it in the electronics. That works as long as nobody fiddles with the bass-mid-treble tone controls on the mixing board. I use the same trick for getting a full-range signal into our YouTube livestream, though the highs will be rolled off slightly by the 100 feet or so of single-ended audio cable connecting the control-room output of the mixing board to the computer running the livestream. That all works far better than it has any right to, given how cheaply I made that work during Covid.

When I play recorded music over the PA system, I have to use channels on the mixer where I compensate for the emphasis of the speakers somewhat by cranking up the bass. It's acceptable but not at all perfect. We do that about once every five years, usually for a specific request for a wedding or a funeral. We don't do media presentations in that space.

The little JBLs are really efficient because of their column-array multiplication, but only at higher frequencies given the tiny size of the drivers. They don't need much amplification at all to do what we ask of them. And they do it unobtrusively, either visually or acoustically.

I would not use these for home playback, though in a room with a bad ceiling reflection they might be useful when coupled with subs.

Rick "as any musician can confirm: sounding good at three feet ain't the same as sounding good 'out front'" Denney