speakers immune from room effects. can this even be possible?

[DocG]

Like I mentioned in your other thread; I need to confirm with JBL their CBTs can be used in apartments, rather than only in large spaces.

I just dropped the Belgian distributor a mail. Let's see who answers first.

Got a reply this morning. The CBTs are developed for large spaces, but if I want to use them in a living room, the CBT50LA is best suited (combined with a sub, obviously). He doesn't say why the 50 would be better though.

Also asked him if I could demo them in my neighbourhood...

 

[DocG]

if you're interested you might check out this thread where a guy reports how he dealt with the kit:

http://www.amb.org/forum/new-speaker-fi-audio-artistry-cbt36-t1887.html?sid=38c7a6593838355c8ccd20b006df2f89

Phew, I just read the whole thread. Looks far too ambitious for me to bring to a good end. And having it done by an electrician (paid per hour) will make the price skyrocket.

 

[oldric_naubhoff]

I presume the manufacturers haven't heard of room modes (or physics) Even if the speakers self eq'ed how would they do this?

the speakers create much more even and broader soundfield which in turn excites most room modes in your room and through that the modes would tend to cancel each other out. as in case of using one subwoofer against 4 or more in a room. furthermore, almost all speakers available are not made to be true point sources. they would only mimic point source operation on one axis. so they are optimised to create even soundfield on only very narrow fraction of space. off-axis you get severe side lobes reflect as well and contribute adversely to overall quality of sound. this is how a 2-way with L-R xover looks like in vertical plane:

you can imagine it'll be even worse in case of higher order way speaker because more points in freq spectrum at which drivers overlap (there's a proviso to that but it's outside of this topic).

so basically, most speakers naturally sound bad because they create uneven soundfield which needs to be catered for in an echoic environment, like with use of your absorbers or diffusers. or you should listen to your speakers in an anechoic chamber. but such luxury is not granted to most audiophiles.

you ask how the speakers can EQ themselves. well, the answer is simple: Lagendre shaded spherical transducer offers wide and uniform soundfield in horizontal and vertical plane within given boundaries as specified by the cap's arc degree.

I wonder if they make you more attractive also?

this remark is completely unnecessary.

if you want to learn more about CBT I recommend Don Keele's web stie or Audio Artistry on CBT 36 (Google that shouldn't be too difficult). you'll find plenty of white paper, including scans of original military R+D on CBT and Don's AES papers (I presume you know what AES stands for).

 

[oldric_naubhoff]

I'm wondering by what sort of witchcraft or sorcery these CBT speakers avoid nearfield comb effects?

Did they not do the schoolboy physics experiment where you put 2 vibrating paddles in a dish of water?

there's no whichcraft involved. only solid science. the speakers' design is based on military research on constant directivity transducer to work underwater from the 70's. why they needed this kind of knowledge is unknown to me but the fact is the research team came up with a solution. if you have a transducer in shape of a spherical cup (like cut away section of a sphere) and then you apply amplitude shading on the drivers further away from the centre of the cup derived from Lagendre equations, you get a transducer that will exhibit very even soundfield in vertical and horizontal plane defined as 66% of the arc degree of the cup. depending on the size of the cup you get different cut-off frequency at which constant directivity kicks in below that you should get omnidirectional behavior (depending on wave length), but you know that. even soundfield means no off-axis side lobes in frequency response of any kind. or in other words you get on axis performance from that transducer regardless where within CBT operational area (remember 66% of cup's arc) you take measurements. outside that area you get output depression but still no lobes.

now, in case of CBT line arrays. Don Keele together with another guy came up with an idea to use this Lagendre shading to a curved line array (the curvature represents cut-out piece of a circle in this case). that way the got a speaker that maintains constant directivity regardless of frequency above CBT cut-off frequency in vertical plane. in horizontal plane such array does not maintain constant directivity, but still behaves much better than most (all?) other speakers available. essentially you get the same frequency response on horizontal plane within 150 deg. cone. what's most important; you don't get side lobes from interaction between drives. some of JBL's CBTs are straight but this is no problem as when you apply gradual delay circuitry to drivers away from the centre of the array you get apparent curvature of the array.

as for your picture. obviously the speakers do radiate sound waves thus the sound waves will reflect off boundaries. but due to the fact the speakers create even soundfield the reflected sound won't contribute negatively to the perceived sound quality. human ear does filtering out of reflected sound pretty well. it's timbre changing inconsistencies in freq response that are irritating to ear. it's just like playing an instrument in damped and reflective room. in either case you'll get different flavor but you'll know this is the sound a given instrument makes. however, in case of most speakers available they are able to convey purity of timbre only when listened on axis in an anechoic environment.

I recommend you take a look at Don Keele's web site or Audio Artistry or JBL to learn more about CBT technology. especially in case of Don Keele's and Audio Artistry sites you'll get plenty to read and plenty graphs to analise. I'd start with those two:

http://www.audioartistry.com/brochures/B&W%20801%20vs.%20CBT36%20Ground-Plane%20Measurements%20v8.1.pdf - comparison of in-room performance of B&W 801 and CBT36

http://www.audioartistry.com/Papers/CBT%20Paper6%20PerformanceRankingof%20Line%20Arrays.pdf - comparison of sound propagation between different types of line arrays.

CBT really works as advertised.

 

[oldric_naubhoff]

Got a reply this morning. The CBTs are developed for large spaces, but if I want to use them in a living room, the CBT50LA is best suited (combined with a sub, obviously). He doesn't say why the 50 would be better though.

Also asked him if I could demo them in my neighbourhood...

bummer.

I asked tech support rather than sales reps the same question. I'm hoping a person in the know would answer.

 

[oldric_naubhoff]

And having it done by an electrician (paid per hour) will make the price skyrocket.

if I were to resort to electrician's help with this project I 'd try to agree to a fixed fee for the project, rather than paying hourly rate.

 

[Clare Newsome]

One of the reasons (other than the fact that they look and sound phenomenal) B&O's BeoLab 5 speakers are my lottery-win dream is that they use Adaptive Bass Control to adapt their output to suit your room. The noise they make while measuring is rather scary, mind you....

 

[DocG]

One of the reasons (other than the fact that they look and sound phenomenal) B&O's BeoLab 5 speakers are my lottery-win dream is that they use Adaptive Bass Control to adapt their output to suit your room. The noise they make while measuring is rather scary, mind you....

ABC works remarkably well, indeed. And B&Os have a rather broad sweet spot, with their acoustic lenses: a big plus for use in a living room. I'm not sure what holds me back (talking Lab9s here; let's stay realistic), but I miss something Maggies do provide, and -- in a different way -- Avantgarde horns.

The CBT speakers seem to collect many of the virtues of these other designs (and more): huge sweet spot, micro- and macrodynamics, a small footprint and thus an exceptional WAF (IMO). But no deep bass -- make that: no bass at all for the JBLs.

The proof of the pudding is in finding a dealer with a demo pair, of course...

 

[hooflungdung]

if something is designed for an untreated environment, then show it off in an untreated room. the room in the video had as much heavy drapery as to cover the stage at the royal albert hall.also a gigantic wall unit & we never saw behind the camera man. Also the photo from 'Stereophile' had enough drapery to be almost anechoic. If there was a smiley with a bloke scratching his chin saying 'Jimmy Hill',i would put it here. If i am walking around a room listening to music then i am at a party & too drunk to be bothered about nodes etc .Part of the trick of good hifi is to treat your room to use reflections that enhance the liveleness of the music & remove or break up as many reflections that muddle the sound. P.S does the designer have shares in the driver manufacturer?

 

[DocG]

I've got news, Oldric.

The other day, I spoke (on the phone) with an interesting man, whom the JBL distributor had pointed me to. He's an EE, with 35 years of experience in the live sound business. He was intruigued why I asked for CBTspeakers. He had studied and tested them for a good while and knew the concept through and through. As a matter of fact, he was just doing tests on how to properly integrate subs with the JBLs. So that was good! The other good news was that he had them on demo (both the 100LA and 70) and invited me to come over and have a listen. The not so good news though is that in his opinion the JBLs are not suited for hifi (has to do with the distance between the drivers or something... went far beyond me).

But he was very positive on the CBT36s, though it would be expensive to get them to Belgium (kit+shipping+taxes+finishing). So yesterday, I had a look at the CBT36 vs. B&W slides: astounding!

I certainly plan to go and see him, for a more in depth discussion of my needs and his suggestions. It's a 100 km drive, so that's doable on a day off. If I learn something interesting, I'll be glad to share! To be continued...

 

[JMacMan]

One of the reasons (other than the fact that they look and sound phenomenal) B&O's BeoLab 5 speakers are my lottery-win dream is that they use Adaptive Bass Control to adapt their output to suit your room. The noise they make while measuring is rather scary, mind you....

I agree, and when I get my pair, then my Lab 9's will move to the surround position!

The other interesting aspect of the design with the ALT lenses, in the context of this thread, is that the power, or polar response is virtually flat throughout 180 degrees in the horizontal plane when viewed in plan; and around 30 degrees in the vertical, albeit the lenses are designed to minimise ceiling and floor reflections - this being an outcome of the research that B&O, Kef and a Danish University did via the Archimedes project into the speaker/room inteface and psycho-acoustics.

As such, for a listener the direct and reflected sound is to all intents amplitude and frequency response near equal; whether this gives the speaker it's sonic advantages in authentic tonal timbre of voice and instruments is hard for someone like me, an HiFi amateur, to say; however the mathematics and the measurements back up the theory of the lenses, as does the listening in my experience of them.

I've been 'firmly' told by a *cough* well known active speaker manufacturer that the ALT lenses are simply an excercise in pointless engineering and sales spiel, and it has all been done before and failed etc, but I prefer to believe that the mathematics and the measurements don't lie, - the laws of science and physics being what they are - and I think anyone who has actually heard them would tend to agree.

Not many people see B&O as a company pushing the boundaries of the state of the art in loudspeaker design, but the B&O ALT range does something re sonic authenticity that no conventional MDF ported speaker box has been able to approach in my experience of HiFi in the 40 odd years I've been involved in the hobby.

JB

 

[DocG]

I've got news, Oldric.

The other day, I spoke (on the phone) with an interesting man, whom the JBL distributor had pointed me to. He's an EE, with 35 years of experience in the live sound business. He was intruigued why I asked for CBTspeakers. He had studied and tested them for a good while and knew the concept through and through. As a matter of fact, he was just doing tests on how to properly integrate subs with the JBLs. So that was good! The other good news was that he had them on demo (both the 100LA and 70) and invited me to come over and have a listen. The not so good news though is that in his opinion the JBLs are not suited for hifi (has to do with the distance between the drivers or something... went far beyond me).

But he was very positive on the CBT36s, though it would be expensive to get them to Belgium (kit+shipping+taxes+finishing). So yesterday, I had a look at the CBT36 vs. B&W slides: astounding!

I certainly plan to go and see him, for a more in depth discussion of my needs and his suggestions. It's a 100 km drive, so that's doable on a day off. If I learn something interesting, I'll be glad to share! To be continued...

Yesterday, I went to meet the man I mentioned above. We had an interesting talk on different speaker concepts, and the influence of the room on them (He was particularly fond of open baffle systems, and - understandably - not so happy with 'modern' architecture. 'Less is more', especially more messing up the sound ).

And then we listened to the JBLs. Well, I understand that they are exceptional for large spaces (church, conference hall, ...), especially for speech. But they are indeed no hifi speakers. Most remarkable is their "sweet spot", which is not sweet at all: while the sound (loudness and quality) is extremely even when walking through the room, it is clearly worse in the "sweet" spot, where sibilance and harshness rule. That is a conceptual issue - no way around it (you can't solve this with DSP without making the rest of the room sound dull). The 100LA was noticeably worse than the 70 in this respect. And the 100LA's sound pressure clearly drops below 200 Hz, which necessitates dual subs. And they apparently are really difficult to blend properly. End of the JBL story for me.

Now Don Keele's CBT36 speaker stays on my radar. I'll contact Parts Express to figure out how and at what cost I could have a kit delivered in Belgium, or better still, if they are willing to send me the computer drawings of the enclosure, so I can have it made here. If so, I'll ask my carpenter what he thinks. And finally I need spousal approval for these somewhat weird looking and rather large speakers... But no need to upset my OH unless all is practically feasible!

 

[DocG]

Still exploring my options, I contacted Parts Express (who distribute the CBT36 kit worldwide). Buying the electronics + the CAM-drawings of the cabinets (without actual cabinets) is not possible. But shipping the whole lot, including the cabinets, to Belgium (with UPS) appears to be far less expensive than I had feared. Add a 'broker fee' and the import taxes (roughly 25% of kit + shipping), and I could have them delivered to my door for under €2100. I guess I'd better have them properly insured during transport, so I must add those expenses too. But so far, it looks doable.

Next hurdle: cost for veneering and lacquering. And then find some one who can handle a soldering iron, and is willing to teach me how to use that...

It's a funny thought. So far, my "longlist" for speakers in the new living room [that is another project than the Devialet] consists of 3 sets, and I haven't heard any of those yet! It should be possible to demo the Avantgarde Zero 1s, before I decide (promised for Q3 or Q4 of 2013). Buti if those are not completely satisfying, I'll have to rely on an educated guess between these CBT36s or a pair of 'Gunned' Magnepan MMGs... Unless something all new and unexpected comes along, of course!

[Edited for spelling.]

 

[DocG]

Oh, and I found a nice discussion on the CBT36 on DIY Audio (http://www.diyaudio.com/forums/multi-way/165596-constant-beam-width-transducers-line-arrays-8.html), with several contributors who know a thing or two about speakers. On page 8 (post #79) even Don Keele himself pops in, unfortunately for no more than 1 post... Some posters, who heard the speakers, are rather positive, but not unanimously so ("lacks the smoothness and musicality of a top speaker")... Makes me a little more reluctant again... :?

 

[matt49]

All very interesting, but as you say a stab in the dark. At least with the "Gunned" Magies you know more or less what they'll sound like: Maggies, only better.

I'd be very reluctant to take a punt on the self-build project. It's not just the money, it's also the time.

:cheers:

Matt

 

[jiggyjoe]

These have got to be worth a listen. http://www.essenceelectrostatic.com/

 

[DocG]

I think you're right, Matt.

This speaker does many things very well (if the theory is correct -- and I think it is, after hearing the JBL CBTs), most of all the room-wide 'sweet spot' [could make me a social audiophile, how about that for a paradox!], with the speakers minimizing ceiling reflections and making use of the floor reflections to enlarge the image...

But apart from the money and time it will take to assemble the kit, it's this quote (from one of the few people who heard the speakers, and posted their impressions - a forum moderator btw) about the sound lacking smoothness and musicality that disturbs me most of all. Because that is exactly what was wrong with the JBLs...

i'll wait for the Avantgardes to arrive first! And then maybe I'll be so impressed by the Vivids that they make it to the living room, who knows!

:cheers:

 

[DocG]

These have got to be worth a listen. http://www.essenceelectrostatic.com/

Yeah maybe, if they ever make it to Belgium... About half a year ago I contacted their sales director, Bob Rapoport, who said he could get a demo pair in Antwerp by July, then September, and I haven't heard him since. I'm not stalking him, cos the shop where they would be on demo also does Avantgarde, and since the Zero 1 is also (very) late, I'm waiting to possibly combine the two demos. Could be a fun shoot-out! But I guess that'll be for next year!

:cheers:

 

[Native_bon]

These have got to be worth a listen. http://www.essenceelectrostatic.com/

More interested in the HDACC DAC... Another way to make money? :clap: I think most people are becoming wise now about new ways to get hands on our money.. But some how something tells me the audiophile in me is still curious... :doh:

 

[Native_bon]

Well its actually been mentioned on whathifi pages here

http://www.whathifi.com/news/cyp-unveils-au-a300-multiroom-amplifier-and-au-d250-dac

Edit: dnt mean to go off topic. just found it interseting