Which 8" coaxial ?

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#21
Ile said:
That wont happen with PA coaxials designed for 2-way, those have separete HF wave guide.
http://profesional.beyma.com/ingles/pdf/8CX300Nd.pdf

Ofcource there is no free lunch, I guess that bit rugged LF responce is caused by that horn.
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It's true that they don't have the same issues but by that point I'd rather just use a classical horn/mid combo. Only coaxials where the cone itself acts as a waveguide are interesting... those kind of coaxials don't really interest me.
 
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#22
Beyma 8BX....not much power but nice sound. Very very nice. Hi-fi. Almost studio...
For wedges I use Beymas as well but 12kx and 15kx......it is also good sounding not so hi-fi......but foor so cheap units....
What about some 10'' compromise?
Regards, Taj
 
#23
Having never tried any of these drivers (yet), how far down the food chain are the Eminence coax drivers, such as the Beta8CX? It is quite affordable in OZ and might make an OK BLH/Reflex box with a MiniDSP to flatten it out some.

I know the answer is to buy one and try it, but there are about 11 things above it in the 'todo list'. So, just interested, really....
 
#25
Brett said:
And what's it going to do to the mids shadowed by the horn?
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My understanding, based on an article I read from Australia, is that the horn really only suppresses the lower midbass response, not the midrange. Their solution was to add a second woofer of the same size and pad it down 6 dB, or something like that. I don't have any personal experience with these however.
 
#26
RockLeeEV said:
The common theme is that with the smaller drivers, a 3-way is necessary to take away cone movement. Either way you don't want to run any of the above full range - a high pass filter + subwoofer is still necessary even for the 15s.

I guess at the end of the day, what kind of directivity sounds best? Some people argue that directivity should be constant and narrow over as much of the bandwidth for best imaging and timbre, for them the 15" and 12" are probably the way to go. For others the 8" is probably a good idea as it's pretty close, but a lot smaller. And for people who feel most comfortable with classic wide directivity the KEF drivers sound like a nice choice.
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Thanks for the very interesting ideas.

So, if the waveguide for the 12" and 15" coaxials are larger, does that also mean that the tweeter can be crossed over at a lower frequency? I see for example that the 12" B&C coaxial can be crossed over at 1.2 KHz, whereas the 8" version is supposed to be crossed over at 2.2 KHz. I suppose this is probably mostly due to the much larger voice coil in the 12" tweeter than in the 8". (3" vs. 1.4")

For me personally, I have high frequency hearing loss and tinnitus, so the response above about 10 KHz is unimportant to me (or should it?). I can barely hear 8 KHz now...

How does the imaging compare between one of these really high quality coaxials and a regular woofer + horn tweeter?
 
#27
So, if the waveguide for the 12" and 15" coaxials are larger, does that also mean that the tweeter can be crossed over at a lower frequency?
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The larger woofers tend to use 1.5" or 2" compression drivers instead (although the 12" radian can be had with a 1" compression driver). The tradeoff is generally in the top octave. You could argue that an ideal speaker would mate a 3/4" compression tweeter to a 12 or 15" woofer, but that's not very realistic because of power handling requirements even in-home. a 1" compression tweeter can usually work in-home but not for professional applications.

I see for example that the 12" B&C coaxial can be crossed over at 1.2 KHz, whereas the 8" version is supposed to be crossed over at 2.2 KHz
. I suppose this is probably mostly due to the much larger voice coil in the 12" tweeter than in the 8". (3" vs. 1.4")

It's moreso about the directivity match. Basically the 8" and 12" cones respectively will designate the tweeter's off axis response, whereas for the woofers, the direcitivity will be increasingly narrow as frequency rises. So the crossover point is best determined by the point where the tweeter's off axis response matches the woofer's off axis response.

For me personally, I have high frequency hearing loss and tinnitus, so the response above about 10 KHz is unimportant to me (or should it?). I can barely hear 8 KHz now...
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I'd still prefer a 1.4 or 1" compression tweeter over a 2".

One thing some do is add a ribbon super tweeter running from ~10khz to 20khz at about 6db/octave just to fill in the response.

It's really up to you. The B&C 12CXT could be a good choice but it will ultimately depend on the crossover; same with the Radian.

How does the imaging compare between one of these really high quality coaxials and a regular woofer + horn tweeter?
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It should be very stable and well defined, especially in a very aggressively rounded low diffraction box. I don't recall the exact polar patterns though, so i don't know what kind of presentation you should expect.
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#29
Brett said:
That's counterinuitive to me. At lower frequencies where the WL are longer the flare would be more invisible (smaller acoustically) to them and so have less effect.
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Wouldn't that be because sound waves are more attenuated when going through a "hole" that's smaller than half their wavelength ?

Anyway, for coaxials that aren't like this Beyma with a real HF horn, is it really the LF cone that acts as a horn/ wave guide, or is there a very small horn behind the dust cap ?

Other question : if the LF cone creates FM distortion, how is it different from the highly praised wideband speakers such as Fostex et al. that get used all alone ?
 
#30
David dP said:
Other question : if the LF cone creates FM distortion, how is it different from the highly praised wideband speakers such as Fostex et al. that get used all alone ?
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Because not everyone praises those wideband speakers ;P

Those full range drivers operate through cone breakups and beam the upper octaves heavily. A coax will have wider, more consistant dispersion, and will use a tweeter in the woofer's breakup range. The KEF coaxial for example uses aluminim or magnesium cones which are pistonic in their passband and otherwise dealt with in the crossover.
 
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#35
David dP said:
OK thanks, that's what I thought...
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And so do almost every other coax - at least every one I have ever seen or owned, including Tannoys (several sets of Red/Gold/HPD), the three different PAudio I have here now, every Beyma and B&C I've seen as well as some vintage stuff. You need something to transition from the CD throat to match it to the cone and some do it better and some do it worse.

WRT to Fostex, I would rather listen to a good multi way with a chainsaw running in the room than every Fostex FR I've heard.
 
#37
David dP said:
I totally agree. That was the reason for my question ! I can only image a coax being "better", in the sense that it has a real HF driver, although not a high-end one.
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Don't sell CDs short. Great ones are great, and better than most domes I've used. There are some ribbons ot AMTs I'd consider in their place such as a Beyma TPL150H, but it's not coaxial.
 
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