I had missed this thread completely (internetless holiday second half of August -- my therapist says it's good for me!).
I've now done some reading, mostly on the JBLs (I'm somewhat put off by the DIY aspect of the CBT36). Apart from the CBT100LA, there's also a CBT50LA and a CBT200LA, with half and double amount of drivers respectively. They have the same freq. response, the most obvious difference being lower/higher SPLs, but I notice some more differences. The vertical coverage is fixed at 20° in the 50 (I guess that won't be too much of a problem). But then they mention the 'Pattern Control Frequency', at 1500 and 600 Hz for the 50 and the 100 respectively. Does that mean the Constant Bandwith Technology only works properly from this freq. and up?
Yes, there's a lot to be said for line arrays when it comes to in-room dispersion. The curved line array approach of the CBT's looks interesting.
As well as good dispersion, line arrays also give you better power handling. If you use the right number and type of drivers wired in a combination of in series and in parallel you can also end up with gentle impedance characteristics. Another benefit is that the soundstage can have height, as opposed to dual concentric designs where the whole band or orchestra sound as if they are on a flat horizontal plane.
The downside of line arrays is the cost of the all those drivers, as well as the cabinets. Also for nearfield listening you get comb effects. And if you're using small drivers you need equalisation for extended bass, or additional large drivers.
Overall, I think there's a lot to be said for line arrays. And there's nothing new about them. They've been around since at least the 1960's.
Line arrays are often used for PA systems, and you can find them in halls, theatres, cinemas, etc. You can make them more directional by building in time delays to some of the speakers (as happens insome sound bars). Unless you are using them in a field, Ideally they should be designed for for the shape and size of your room. If set up correctly they do work, by adding constuctively to the direct sound, while the timing of the echos is effectively spread, smearing them out. All you need is money for a specially designed set. I'm not so sure about off-the-peg ones.
(internetless holiday second half of August -- my therapist says it's good for me!).
I guess I need to have such a therapy myself (now where would I go? maybe central Algeria? )
correct. but it's 1500Hz and 1000Hz. that's why 100s should be a better bet. 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 know using a CBT array in apartment shouldn't be a problem with CBT36 because I saw measurements taken a few inches in front of the baffle and then a few metres away and they virtually don't change save for a slight decrease in overall level, but that's quite understandable that volume decreases with distance. however, with array this is much less than in case of a typical point source or quasi point source (like 2-way bookshelf). typically you loose 6dB of output for every doubling of distance with a point source and only 3dB with a line array. and this is a good news for your amp if you believe in superiority of power quality over quantity. I'm just hoping that in case of JBL's arrays they perform similarly nearfield which would make them suitable for home use.
the 200 looks interesting too but I'd confirm first if such a long array would work well in a room with so narrow vertical boundaries. I presume your room is typical 2.5m high. but if it could be used that way it literally means a wall of sound in your apartment! say bye-bye to shrunken stereo images.
Giro, InTheGroove, Digit, ClassicOne, MG12
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.
I know using a CBT array in apartment shouldn't be a problem with CBT36 because I saw measurements taken a few inches in front of the baffle and then a few metres away and they virtually don't change save for a slight decrease in overall level, but that's quite understandable that volume decreases with distance.
I guess it wouldn't be wise to get the CBT36 as a first DIY experiment; still toying with the idea to have it finished and put together by my carpenter and electrician. That would raise the cost, but it might still be acceptable (JA in Stereophile quotes $8500 for a finished pair!)...
As well as good dispersion, line arrays also give you better power handling.
truth is most line arrays don't offer all that good dispersion. especially those with evenly driven drivers. you get severe lobes off axis that don't contribute to good sound quality.
Also for nearfield listening you get comb effects.
the beauty of CBT is that you don't really. you essentially get the same freq response regardless of distance from the speaker, save for slight drop in level further down the room. that means inches and metres away from the baffle you get the same sound.
And there's nothing new about them. They've been around since at least the 1960's.
quite right but CBT is based on military research in the 70's which were declassified in the 80's. it took another few decades for some forward thinking people to come up with an idea that this research could be used for building speakers. IIRC Don Keele started to work on CBT prototype around 2000.
AFAIK finished speakers are not available yet and I don't know if they ever will be since no sign of them so far.
as for assembling the kit; I guess you won't need a carpenter because the cabinets will come in fully assembled. as for electric work inside it's very easy, you just need to connect the drivers and resistors as required but the manual is said to be very thorough. it's just the bulk of work that may seem overwhelming. the only tough part where you might need some help is checking if the drivers' phasing is OK for which you'll need some extra electric testing equipment and then painting of the cabinet (if you want good effect go for car paints but then you'll defo need professional help) or veneering (in which case a carpenter might be useful).
if you're interested you might check out this thread where a guy reports how he dealt with the kit:
I presume the manufacturers haven't heard of room modes (or physics)
Even if the speakers self eq'ed how would they do this?
I wonder if they make you more attractive also?
General Manager GIK Acoustics Europe
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?
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...
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.
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.
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).
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-... - comparison of in-room performance of B&W 801 and CBT36
http://www.audioartistry.com/Papers/CBT%20Paper6%20PerformanceRankingof%... - comparison of sound propagation between different types of line arrays.
CBT really works as advertised.
I asked tech support rather than sales reps the same question. I'm hoping a person in the know would answer.
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.
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