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

[Alice of Old Vincennes]

I have designed a (relatively) simple, passive speaker that approaches a very narrow CBT response vertically. If anyone is interested in these types of designs, they can get their feet wet for only $750 a pair, which gets you all the drivers, all the crossover parts, and flat pack cabinets (that still require cutting holes, and building an internal enclosure for the mids).

http://techtalk.parts-express.com/f...owers-nested-array-speakers-in-denovo-cabinet
http://projectgallery.parts-express.com/speaker-projects/skylark-flying-towers/

Comparing these to traditional speakers, here are some of the observations that I have heard, or which others have communicated to me:

Enhanced clarity, while maintaining a wide soundstage.

Consistent spectral balance throughout the room, and even into other rooms on the same floor (while traditional speakers get dark the farther away you get). This ended up being a major reason that my co-worker built a pair. This feature allowed him and his wife to enjoy music more.

Brighter sound. I prefer a response that tilts down a bit on speakers like this. I suspect that the floor and ceiling reflections have a tendency to shift the perceived spectral balance (making it darker) and when you suppress those, a flat speaker can sound bright and very unforgiving. Perhaps the JBLs didn't cause this in part because they aren't actually reducing the floor reflection significantly. The narrower the beam, the more difficult it is to maintain consistency.

High dynamics. This comes with having the extra drivers it takes to achieve the narrow beam.

High measured sensitivity, but not as high perceived. For a traditional speaker, there's typically as much or more energy arriving from the vertical reflections as there is direct sound. Reduce those reflections significantly, and you reduce the perceived loudness. I suspect this same reduction in perceived loudness also impacts the perceived strength of the lateral reflections. Since they don't have to compete with vertical reflections, the strength of the lateral reflections is relatively enhanced. This can be a benefit if you can manage a bit of space, or if you diffuse the first reflection points (if they are too close).

A greater ability to disappear, and let the spatial cues in the recording come through.



I haven't heard the JBLs. The measurements look pretty nice, except for the resonance we're all waiting to hear an explanation for. I do think that it takes two speakers to appreciate the soundstage and imaging differences associated with this type of speaker. I wonder if Amir will be intrigued enough to set up a stereo listening session somewhere, somehow, and report his experience. Perhaps the owner will comment.

Gee, Ben or JBL?

 

[Ericglo]

Thanks Amir for testing these. One of the speakers I have been most interested to see.

Archaea is the owner and gave his thoughts on their usage in his theater. Maybe he will repost here.

Don Keele is one of the primary patent holders for CBT tech. He has some really good videos that explain the soundfield. This presentation compares a floor standing CBT to the older B&W 801....

http://audioartistry.com/brochures/B&W 801 vs. CBT36 Ground-Plane Measurements v8.1.pdf

CBT tech is derived from work the U.S. Navy did back in the '70s and '80s with sonar technology. Think one ping only.

https://www.xlrtechs.com/dbkeele.com/CBT.php

Beat me to it.

Don Keele really brought these to life. Rick Craig has worked with him and produced his own CBTs.

Don did some youtube videos if anyone really wants to get into the details.

 

[Ericglo]

I have designed a (relatively) simple, passive speaker that approaches a very narrow CBT response vertically. If anyone is interested in these types of designs, they can get their feet wet for only $750 a pair, which gets you all the drivers, all the crossover parts, and flat pack cabinets (that still require cutting holes, and building an internal enclosure for the mids).

http://techtalk.parts-express.com/f...owers-nested-array-speakers-in-denovo-cabinet
http://projectgallery.parts-express.com/speaker-projects/skylark-flying-towers/

Comparing these to traditional speakers, here are some of the observations that I have heard, or which others have communicated to me:

Enhanced clarity, while maintaining a wide soundstage.

Consistent spectral balance throughout the room, and even into other rooms on the same floor (while traditional speakers get dark the farther away you get). This ended up being a major reason that my co-worker built a pair. This feature allowed him and his wife to enjoy music more.

Brighter sound. I prefer a response that tilts down a bit on speakers like this. I suspect that the floor and ceiling reflections have a tendency to shift the perceived spectral balance (making it darker) and when you suppress those, a flat speaker can sound bright and very unforgiving. Perhaps the JBLs didn't cause this in part because they aren't actually reducing the floor reflection significantly. The narrower the beam, the more difficult it is to maintain consistency.

High dynamics. This comes with having the extra drivers it takes to achieve the narrow beam.

High measured sensitivity, but not perceived as high. For a traditional speaker, there's typically as much or more energy arriving from the vertical reflections (combined) as there is direct sound. Reduce those reflections significantly, and you reduce the perceived loudness. I suspect this same reduction in perceived loudness also impacts the perceived strength of the lateral reflections. Since they don't have to compete with vertical reflections, the strength of the lateral reflections is relatively enhanced. This can be a benefit if you can manage a bit of space, or if you diffuse the first reflection points (if they are too close).

A greater ability to disappear, and let the spatial cues in the recording come through.



I haven't heard the JBLs. The measurements look pretty nice, except for the resonance we're all waiting to hear an explanation for. I do think that it takes two speakers to appreciate the soundstage and imaging differences associated with this type of speaker. I wonder if Amir will be intrigued enough to set up a stereo listening session somewhere, somehow, and report his experience. Perhaps the owner will comment.

What about the tweeter? I looked the other day and it is no longer available.

Are these the same speakers that left Dennis Murphy speechless? I would love to see Amir or Erin measure your speakers.

 

[BenB]

What about the tweeter? I looked the other day and it is no longer available.

Are these the same speakers that left Dennis Murphy speechless? I would love to see Amir or Erin measure your speakers.

I hadn't noticed that the tweeter is no longer available. Thanks for bringing that to my attention. I will edit my first post in this thread.

If one of my speakers left Dennis speechless, it would have been the big brother to the skylarks, which I refer to as the Radicals. Dennis heard the skylarks, but I don't think he managed to really get past the spectral balance issues. They are designed to be augmented with a subwoofer, but I don't believe he had one handy. Also, I believe he thought the tilt I added was excessive. So he ended up listening to a speaker that he felt had no highs, and no lows. In contrast, my co-worker found the skylarks with the spectral tilt were still perceived as slightly brighter than his Definitive Technology towers (which the skylarks replaced).

 

[rockyb]

From what I read above, I suspect a good analogy is of that to a point light source, like an LED with a large convex optical lens where the LED is at the focal point. The apparent distance (used in inverse square law) is altered by the lens and increased toward infinity. Thus the beam of light from the LED is focused or columnated so there is little falloff with distance. Of course, the Amir's test results show this works better on one axis than both.
Still wondering how this would be in a home theater application, where the center speaker would be mounted above or below a flat screen LCD TV?

 

[Linus]

@amirm The measured performance doesn't really correlate with your strong recommendation IMO.

Perhaps the novelty, unconventional design and the CBT 'magic' is influencing you? Based on your measurements, I wouldn't bother with these for anything other than a small exhibition or conference room, but certainly not in the home. What do you think?

Terrible Preference Rating and quite expensive ($1050 each). Why would you want those? Speakers with better measurements got worst review. Am I missing something!?

 

[Sancus]

Terrible Preference Rating and quite expensive ($1050 each). Why would you want those? Speakers with better measurements got worst review. Am I missing something!?

This is half of a speaker, they come with a bass module they're supposed to be used with, so the preference score isn't precisely accurate as they obviously have no bass. Though I suppose you can certainly use a sub, but the crossover is high enough that I think they would need to be co-located.

In addition to that, 0 of the speakers in the Olive study were anything like a CBT so the formula is pretty off in the weeds here, I doubt the model is valid.

I would consider the preference score a curiosity for this one, at the most.

The purpose of this speaker is to maintain even SPLs all across large spaces and outdoors, and it does that far better than any traditional design loudspeaker ever could.

 

[Deleted member 2944]

CBT tech is derived from work the U.S. Navy did back in the '70s and '80s with sonar technology. Think one ping only.

https://www.xlrtechs.com/dbkeele.com/CBT.php

Actually, research on this pre-dates that and was pioneered by a couple of defense contractors that have oodles of experience/knowledge with this sort of thing.
US Navy-ish beam-steering sonars are quite a bit more advanced than what we see here with an audio CBT transducer, but the underlying concept is very similar.

Dave.

 

[RealityCheck18]

I built a pair of three-way line arrays around 8 years ago,

Companies were dumping neodynmium drivers like the plague so I purchased crates of them to screw around with line arrays. Initially, went for a dozen 5 inch woofers and 36 then 48 tweeters (10mm ones) in a 6 foot line. That didn't work right so I purchased another box of 50 three inch full ranges and off to the races I went. Set the crossover points for 350Hz and 5,800 Hz and done. Did a bit of EQ in the midrange to calm a peak and boosted 16KHz at +6dB to get it close.

The point of the madness was a garage speaker--wanted something with very wide dispersion horizontally, a 6 foot vertical wall of sound coming at you so it would sound the same sitting down or standing up (garage thing) but not give floor bounce or ceiling bounce to screw things up. My garage has nice, smooth cement which really made a mess of things. After a few failures, some serious tweeking, throw in some EQ and subwoofers it was done. They are placed on push-pull slot loaded subs that stand 20 inches tall and with the arrays, the stack is 7 feet 10 inches (239 cm) tall.

Those things can get really LOUD as 12 five inch woofers, 21 three inch mids and 48 dome tweeters per box easily do. With 200 watts into each speaker, I measured 111 dB at 25 feet (7.6 meters) at the door of the garage. Ultra-wide horizontal dispersion with vertical controlled out to around 4 or 5 meters back before floor reflections hit. You can actually crank them up, walk towards one and press your ear against the 48 tweeter array and it won't blast your ears. It also has about the same volume at 1 foot (30cm) out to 12 feet or around 3.5 meters. This has to do with being on axis VS off axis and the farther back you go, the more speaker go on axis and that counters the increasing distance. Pretty freaky when you hear it do it.

A very fun speaker, they can very very efficient so great for parties in the garage--and in front of the garage. Be aware that the 3dB per doubling of distance only applies to infinite line arrays--all line arrays become point sources past a certain point. The taller the array, the farther away that point is reached and very generally (and broadly) is around twice the distance away from the height of the array gives you near field oddities (the sound level remains very even) At around 4 times the distance VS the height of the array, you start to lose the slow decline and it starts to drop off (depending on frequency)

My arrays are 6 feet or 183cm so are rather entertaining. The best way to show the very narrow vertical dispersion is to place them on saw horses facing straight up and have a person walk beside them--one they step past the last drivers of the array it sounds like you just left the room. Very weird considering there are no horns or anything--you get an immediate drop off in SPL. So yeah, I got to see adults screwing around with them, finding it odd that the SPL didn't change much near field, putting your ears on the tweeter lines or feeling the bass that 6 feet of woofers will give you.

Learned a lot about....woodworking with those things. 3-way line arrays of 6 feet tall is a lot of headaches to just put them together! 162 drivers that need wiring looms soldered in, a double baffle to seal off the mids from the woofers and making sure all those drivers maintain a seal is madening. I won't do it again! You could think 48 tweeters that are at 90dB efficiency would outblast 21 three inch mids at 85dB efficiency---you would think and you'd be wrong!

Good times, good times and they make perfect garage speakers--the dispersion is correct, they sound the same sitting down and standing up (array height is 6 feet) great for partys and so on.

The big question is--are they the "right" speaker for home use? Geez, that is hard to say and I own a pair! When listening to music, they give a very HUGE sound to them because they are huge! This is generaly a good thing but listening to a wall of solo flute is...odd. Maybe the very small "mini-array" as those are would work better in smaller rooms? Having a wall of sound coming at you is a matter of taste, my HT is "point source" which works better for me and pin point clarity.

Glad Amir tested them, always wondered what the robots reaction to so many sound points would be. To get the concept going, forget the small ones and lose your mind with one of Don Keele's CBT "broke back" arrays--I'm sure it will take far more than 2,000 measurements to get the results. Do it for science! If a person is interested in them--best to listen to them because of their distinctive dispersion and weird near field "sound leveling" effects they have. In some cities you can rent those JBLs from pro sound shops which would be fun.

Would I rip apart my straight arrays with no shading and go CBT? No....absolutely not. My goal was avoid floor reflections at all cost and the subs keep them 20 inches off the floor and my ceiling is 10 feet/3 meters which helps there. Some people have built them curved and straight and both of them required EQ to work so not a clear winner either way. If you forced me to build another pair of them, I'd go with the Faital Pro 3" full range neo drivers (25 of them), make the boxes 2 plus meters tall and cross them at around 200Hz to a stack of eight 10" woofers with a healthy helping of PEQ to get them to work. 48 dome tweeters stacked up 6 feet high is not a soldering job I wish to do again--then do it again for the second speaker. You have been warned!

Looking forward to the full JBL system, do some SPL measurements at 1/2/3/4/5 and 6 meters outside in the sunshine to show what happens with distance with that version. Just a simple SPL check and a quick frequency sweep--you can use a point source and put the graphs next to each other to show with measurements what they do.

Truth be told, I did haul them in my living room when my wife was gone for a weekend...good times until she came back. WAF is in negative numbers as they absolutely dominate the room. Alas, they went back to the garage....my narrow coffins got banned. To sum it up, even audiophiles like the goofy things because they are....different. Looking forward to the rest of the array story, they are odd ducks but sometimes having something a bit out there is a lot of fun. Oh yeah, don't lay them on their side like a horizontal center channel.... they absolutely suck that way as they enter acoustic chaos mode on their side. One last tip, if you drink a beer or two--any weirdness they have gets "smoothed" out....keep drinking until they sound great!

 

[Archaea]

@amirm
Thanks for taking the time to test the speaker, and for doing this service to the audio community that you seem to tirelessly attend to!!! I see you will do the bass module next - I suppose they are too tall to be tested together?

As to my experience/opinion on using 13 of these JBL CBT 70j-1 speakers in a 9.8.4 HT setup; I've posted that previously in post 3 linked below, so I'll let you read more there if inclined.
https://www.audiosciencereview.com/...eakers-in-commercial-project.310/#post-435727

In summary, I think they are fantastic. Someone asked about stereo listening. They are a very different sound than what you are most likely familiar with in traditional speakers. They have a sweet spot a mile wide, as in you could literally be in the chair on the either side of the center, main listening position, and it would sound like you are in the main listening position. This compared to many high end audiophile speakers I've auditioned in various home theaters that seem to have a very clear single centered sweet spot about 6" wide.
The CBTs do not have that focused center image sound that a stereo purist might seek, rather it's more of an “all around you" sound. Stereo listening is almost like engaging a multispeaker DSP function. Sometimes when I'm stereo listening I have to double/triple check to see if Dolby Surround or multi channel stereo engaged. With all thirteen speakers in multichannel stereo it's uncanny. I can walk anywhere in my home theater and it all sounds the same. Kneel, sit, or stand. All Uniform sound. No hot spots, no weak spots. With the eight 18” subwoofers, the bass is uniform too. It's a party trick I always show new visitors. Most I've demoed for have never heard anything like it. AND because of the distribution of the sound via the multiple drivers in each speaker you can walk right up to the speaker played at reference volume and not wince. That character makes them a great choice for a surround speaker that has to be too close to a particular seating position.

These JBL weren't my first exposure to CBT / Line Array technology speakers, I've had a few experiences and I've liked all of them.

My first audition was to the AVS123's LS6 and LS9.

I heard them at a few audio meets, and one of my friend's has a pair. They sounded great, but discontinued, HUGE, complicated, and now expensive, I wasn't going to buy a set of 13 of these.

-----------
The second exposure was to a set of Selah Game Changer Line Arrays at a "Heavy Hitters" blind testing audio meet in PA. The Game Changers stole the show for me. They were diminutive, the smallest speaker in the lineup, and I initially smirked that they entered a big boys competition because they had such tiny little drivers. In the blind audition, they filled the room completely - sounding the same everywhere, and blew me away. I had no idea what speaker was playing, but it was my favorite and I was incredibly surprised I picked them as my favorites over the other much more visually imposing candidates. Again too expensive for me, but I sure liked them!

Video footage of that Heavy Hitters G2G and meet. What fun!
(13) Gorilla83's Home Theater Heavy Hitters Meet, with stops at Popalock's, Craig John's, and DMark1's - YouTube
The blind testing day starts at around the 18:30 mark. (Some crazy stuff in this video -- want to see what 16, eighteen inch subwoofers do in a home theater? Skip to timestamp 15:35)

-----------
My third experience hearing a CBT design was at Axpona 2017 when Don Keele (the designer behind the CBT design) helped introduce the Epique CBT24K speaker as an audio speaker in partnership with Parts-Express. I walked by a mammoth pile of speakers (various products P.E. carried) with the CBT24K out front stand alone. As I walked by the display the sound was like a uniform wall, it sounded the same no matter where I walked within about a 20 foot range in the hotel lobby. It truly baffled me because I couldn't tell where the sound sourced from. It wasn't directional and barely changed volume as you walked closer or further away from the stack of speakers? How weird! The buddy I was with asked me if the sound was from the Epique line arrays, since he spotted and recognized Don Keele talking among the passer-bys, and understood the technology more than me. I told him no - it didn't sound like those little speakers could be doing that big sound, so I proceeded to walk up to the mountain of speakers and start putting my ear next the various drivers trying to figure out what speaker was producing such a uniform sound regardless of where you walked ---- were all the speakers on I initially wondered? I came to the realization it was, in fact, the little Epique CBT pair with tiny 2.5" drivers. I was blown away yet again. My buddy and I both bought a pair right there at the trade show floor! Sadly I never got around to putting mine together. My intent was to put them in my living room. Life happens - it's still unfinished. Someday?

-----------
My fourth experience (actually my third experience chronologically) was the local Kansas City AMC Prime movie theater

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 was blown away again. It was my favorite commercial movie theater sound experience I'd ever had - and nothing else was even close. The sound experience was amazing, the music as the credits rolled was utterly fantastic! My buddies and I after the movie spent time commenting on just how excellent the sound was, we took pictures of the speakers, and tried to identify them. I looked them up, $1200 a piece for the mainspeaker CBT 70j-1 and then another $600 a piece for the bass modules CBT 70je-1. Ouch! As you can see in the picture the AMC had a LOT of money in those JBL CBT speakers!
Ugh. Too expensive, yet again, but since these were a mass production speaker I figured I might have a good chance of getting some used cheaper. I set up an eBay alert and got occasional alerts for the next ~ 3 years. Finally an auction popped up locally with 34 JBL CBT 70j-1 that a company had used for a couple 5K races - and had stringed them along the race path (because of the CBT characteristic of losing SPL at half the rate per distance of a traditional speaker). The seller was about 60 miles away so I could do local pickup, and he was selling them cheap. I bought 13 for about $420 each.

There's more to the story, 10 of the 13 had an 8 ohm sandbox resistor that had failed, making a 10dB dip at 2Khz, so I had a LOT of unscrewing and crossover solder work to do, but ultimately I got them all fixed with the guidance of some smart, helpful guys on the DIY board at avsforum - measured with a calibrated omnimic as overlaying each other correctly, and finally was good to go!
All 13 overlay each other correctly when measured from the same position (FR measurements taken indoors inside my home theater room - all from the same position to validate each speaker was working similarly), metal speaker grills removed in all instances — I use them without the grills)

While all were disassembled, I installed the RGB 5050 lighting strips behind the tweeter array to match the AMC Theater look and that's where I now sit.
(I bought three more new last year, to eventually bump my HT system to 16 channels, and Amirm was sent one of the new units, which I tested before hand to verify it overlaid with my current 13 speakers in frequency response perfectly -- it did), so if the unit amirm measured was defective, then my 13 are also defective. (at least based on frequency response taken by my omnimic)

I've been through a lot of speakers in 15 years. (6 entirely different sets in my home theater room. Klipsch, Wharfedale, Elemental Designs, JTR, Mackie, and now these JBL CBTs) These are the first speakers where I feel like I'm done. I've had them now for about 3 years, I have zero intent of replacing them. Similar to my search for subwoofers, with both I've found my own place of satisfaction, and I do not need, or even desire to chase something else.
For cinema, I don't know that I've heard better than these speakers. I've observed that all matching speakers is an incredible boon in the world of atmospheric audio/object based audio, where the Dolby Atmos or DTS-X objects can move between any speaker seamlessly in your cinema, and I'm particularly pleased with the JBL CBTs for that purpose!

Anyway - long read, but I know I like line array and CBT designs from several different experiences, and have further confirmed it with my time of ownership. Your mileage may vary! Thanks again amirm for measuring the speaker and supporting the community!

If any of you are ever in the Kansas City Area and desire an audition of my setup let me know. I enjoy giving HT demos, and talking audio with other enthusiasts.

 

[amirm]

@amirm
Thanks for taking the time to test the speaker, and for doing this service to the audio community that you seem to tirelessly attend to!!! I see you will do the bass module next - I suppose they are too tall to be tested together?

My pleasure. The two may have fit but would have made the sound field even more complex to measure.

 

[Maiky76]

Hi,

Here is my take on the EQ.
The raw data with corrected ER and PIR:

Score no EQ: 2.98
With Sub: 5.85

Spinorama with no EQ:

• Reasonably Flat as i would expect, just the bump around 900Hz
• Great Directivity
• No Bass so Sub score may be more relevant?

Directivity:
Better stay at tweeter height
Horizontally, anything goes almost.

EQ design:
I have generated two EQs. The APO config files are attached.

• The first one, labelled, LW is targeted at making the LW flat
• The second, labelled Score, starts with the first one and adds the score as an optimization variable.
• The EQs are designed in the context of regular stereo use i.e. domestic environment
• Quite a bit of work is required, Pro integration?
• I have added bass boost but it could be removed/altered with a sub.
• Just be careful about max SPL if you boos the LF
• With significant damping in the room the EQ LW might be better

Score EQ LW: 4.43
with sub: 7.18

Score EQ Score: 5.37
with sub: 8.03

JBL CBT70J APO EQ LW 96000Hz
March182021-153023

Preamp: -5.4 dB

Filter 1: ON HPQ Fc 54.8 Hz Gain 0 dB Q 1.19
Filter 2: ON PK Fc 318 Hz Gain 2.3 dB Q 3.62
Filter 3: ON PK Fc 536.5 Hz Gain 2.07 dB Q 3.24
Filter 4: ON PK Fc 706 Hz Gain -1.74 dB Q 4.02
Filter 5: ON PK Fc 946 Hz Gain -3.62 dB Q 5.46
Filter 6: ON PK Fc 1369 Hz Gain 1.46 dB Q 3
Filter 7: ON PK Fc 2001 Hz Gain 1.62 dB Q 4.07
Filter 8: ON PK Fc 6455 Hz Gain -2 dB Q 1.48
Filter 9: ON PK Fc 10504 Hz Gain -3 dB Q 7.33
Filter 10: ON PK Fc 13127 Hz Gain 5.76 dB Q 0.85

JBL CBT70J APO EQ Score 96000Hz
March182021-152809

Preamp: -4.3 dB

Filter 1: ON HPQ Fc 56 Hz Gain 0 dB Q 1.19
Filter 2: ON PK Fc 93.5 Hz Gain 2.43 dB Q 1.72
Filter 3: ON PK Fc 325.5 Hz Gain 1.82 dB Q 3.74
Filter 4: ON PK Fc 541 Hz Gain 2.32 dB Q 3.18
Filter 5: ON PK Fc 718 Hz Gain -2.01 dB Q 2.71
Filter 6: ON PK Fc 948.5 Hz Gain -2.66 dB Q 6.52
Filter 7: ON PK Fc 1368 Hz Gain 0.92 dB Q 2.15
Filter 8: ON PK Fc 2029 Hz Gain 1.72 dB Q 4.37
Filter 9: ON PK Fc 5465 Hz Gain -2.84 dB Q 0.69
Filter 10: ON PK Fc 6906 Hz Gain -1.2 dB Q 3.56
Filter 11: ON PK Fc 10465 Hz Gain -3.1 dB Q 6.63
Filter 12: ON PK Fc 13558 Hz Gain 4.35 dB Q 0.47

Spinorama EQ LW

Spinorama EQ Score

Zoom PIR-LW-ON

Regression - Tonal

Radar no EQ vs EQ score
Great improvements (thanks to the directivity)

The rest of the plots is attached.

 

[daftcombo]

Is it similar to line-array design?

 

[mitchco]

@RealityCheck18 and @Archaea very cool! Speaking of line arrays, I assume you have seen wesayso's build on diyAudio: The making of: The Two Towers (a 25 driver Full Range line array)
Lots of great info, including CBT and the very nice open source DRC DSP.

 

[Rja4000]

Thanks for this very interesting review.

I guess this is inspired by PA line array architecture.
The Wikipedia article on this subject is worth reading.
https://en.m.wikipedia.org/wiki/Line_array

Line array is widely used for big audience PA, since they allow a more stable frequency response and sound level on a very wide area.
And for economical reasons, the trend is to have more and more people in one single concert, so a much wider coverage is a strong economical benefit.

Sound level is key, especially for countries like France, where the SPL is limited by law to 105dB at any location in the venue.
Traditional speaker systems can't do that, since level decreases quickly with distance from loudspeaker. Not with LA.

So that's probably no coincidence that first commercial implementation was done by the French company L-Acoustics and that this is also the base of originaly-french Nexo company's success (now owned by Yamaha)

Typically, for PA, those system are modular, and computer-optimized for each room or venue.
They are also hanging as high as possible, to keep source in direct sight of public.
(have a wall of people between you and the source and the sound will change dramatically)

Using this technology for small rooms has some drawbacks, though, and although the depth of good sound is big, there is probably a hard limit where it degrades a lot.
The vertical directivity may also be a problem...

 

[riffmaker]

That's interesting. I thought sound power dropping proportionally to the square of distance is a feature of acoustics. I had no idea it can be modified.
So does this law work only for traditional speakers? Or does it work for sound generally, with CBTs being an exception?

 

[test1223]

That's interesting. I thought sound power dropping proportionally to the square of distance is a feature of acoustics. I had no idea it can be modified.
So does this law work only for traditional speakers? Or does it work for sound generally, with CBTs being an exception?

It is the none spherical wave. The linearray provides a more cylindrical wave. So the drop of is lower. You can form even a planar wave which has in theory no drop of at all.
Even a normal speaker not necessary provides a spherical waves in all frequency bands, therefore you have some variations with distance of many speakers.

 

[MZKM]

You have the full height of the speaker as far as vertical alignment.

This is what is confusing to me. In the vertical off-axis plots there is no indication that there even is other tweeters playing. I would have thought it would have looked more like an omni-directional speaker in that regard.

______
EDIT: I watched Keele’s video series, and while I know better how they work, I still don’t get the narrow vertical dispersion.

Traditional (free standing) CBT:

For a ground-plane (floor standing) CBT, it cuts the arc in half and uses the upper half:

It can do this by making use of the floor reflections, where due to the constantly curved nature, it emulates the sound from the drivers in the discarded bottom-half:

My confusion though is that this JBL is of the ground-plane design, so how can it properly work when off the floor?

EDIT: The J in the name is for the standard J shape you see at concerts.

It is a hybrid of the delay beam forming and physical arcing. Beam forming (even with digital delay) has limitations due the directivity of the drivers themselves. Physical arcing helps provide constant coverage angles to higher frequencies.

__________

Keele also states that a straight array can be used, but time delay would be needed to compensate for the distance difference, JBL offers both line array & J shape.
__________

However, even in his examples the vertical directivity is not narrow, quite the opposite:

____________

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.

On the notion of measurement axis, James Larson states this in his review of the Parts Express CBT24:

One feature of CBT speaker design is that, the higher you listen to the speaker up to the cabinet’s highest point, the less the SPL will change from distance. At standing height…you can walk back and forth…to a distance of a few meters and experience almost no change in loudness.

I also found this graphic:

I assume this is because all the drivers below the top are louder in 3dB increments, so while the level should drop by 3dB as distance double as a property of a regular line-array, these 3dB louder drivers negate the effect (up until a distance to where the 0dB attenuated base tweeters are in your listening window).
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Amir, going by the polar plots, the Klippel is using 10 meters as the distance; can you recompute this as like 2 or 3 meters? If so, I would expect the vertical measurements to make more sense. Changing the center of expansion towards the top may also make a difference.

 

[fordiebianco]

Don Keele is one of the primary patent holders for CBT tech. He has some really good videos that explain the soundfield. This presentation compares a floor standing CBT to the older B&W 801....

http://audioartistry.com/brochures/B&W 801 vs. CBT36 Ground-Plane Measurements v8.1.pdf

Has anybody ever listened to Don Keele's Epique from Dayton Audio? Always eyed the thing...

 

[tifune]

This is half of a speaker, they come with a bass module they're supposed to be used with, so the preference score isn't precisely accurate as they obviously have no bass. Though I suppose you can certainly use a sub, but the crossover is high enough that I think they would need to be co-located.

The purpose of this speaker is to maintain even SPLs all across large spaces and outdoors, and it does that far better than any traditional design loudspeaker ever could.

Very salient points which I maybe missed in the original review - the MSRP for each module is $1k but if you're diligent you can get each for 1/2 off. For 2 channel I would say the bass module is more or less required. Subs change things as always but personally if I can have extension to 45Hz, even at -10, already well thought out by someone far more qualified than myself for $500/ea I would take it. I believe for wall mounting the bass module needs to mounted alongside the main unit, the official JBL mounts don't support the unified vertical orientation.

The "outdoor" functionality really gets hammered home when you consider the rated specs: a 92dB (roughly averaged for music mode) speaker that can handle 700W continuous, 1000W for 2 hours? Not sure where else you would use that EXCEPT outside. Also, they're IPC-55 rated once coupled with a small boot that covers the input terminals.

I setup mine with a Behringer NX1000, just waiting for weather to warm up to give it a solid test. Probably will use a Qudelix for LDAC/Adaptive APTX and PEQ, and for <$200/ea add more NX1000's if needed. With fans that loud where else could you use NX's EXCEPT outside?

The outdoor grille doesn't look nearly as cool as the xenomorph-styling in this review but hopefully if you're enjoying a warm day you're not looking at your speakers too much. And yes, amongst brand name speakers these probably set a new low for WAF if that's a consideration