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Crazy PA Coaxials for Hifi

I'm a bit older and have been building coaxial speakers for decades.
When Tannoy drivers were easier to buy on the market than they are today, some Tannoys from 8 to 15 inches for friends and me.
Some projects with the Isophon 2000, a 12 inch coax.
I have used PA coax from RCF, BMS, Beyma and B&C.
My last project is an 8 inch B&C coax and I think that's it for now.
I always had man-sized speakers and wanted the same performance in a smaller space, so I coupled two PA 8" coax from B&C to an 80 Hz bass reflex cabinet with an active 18" Beyma Subwoofer.
You can only see the satellites and the maximum undistorted volume of the system is close to the original concert.
The final tuning was a few years ago (2018). I tuned them pretty linear from 80hz. The active 18" Beyma subwoofer takes over the range up to 80hz.

Beyma 18LEX1600Fe

1000023265.jpg


The omnidirectional behavior of this B&C coax is very good, because the small horn has a large opening angle.
I make any changes to the listening position with the DEQ2496 or, since a few weeks, with the WiiM Ultra.

BC Coax 8FCX51-3093 (1).jpg
BC Coax 8FCX51 Messung (1).jpg
BC Coax 8FCX51-5157 LQ (1).jpg


This is a 12 inch pa coax

1000023261.jpg
 
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Thanks, @sigbergaudio . That helps a lot with knowing how far to take the horn design. Happy to learn it isn't detrimental to subjective sound quality. The problems are pretty high up in frequency so I suspected it wouldn't matter very much.
 
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nc535 said:
nice directivity but ugly raw response
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That is to be expected. Off-axis it should already look a lot better, and obviously it will need some shaping, but all in all, super linear frequency response isn’t very high on the list of priorities of such a driver :) Haven’t seen pricing yet, probably €800 or so.
 
voodooless said:
That is to be expected. Off-axis it should already look a lot better, and obviously it will need some shaping, but all in all, super linear frequency response isn’t very high on the list of priorities of such a driver :) Haven’t seen pricing yet, probably €800 or so.
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And I do expect it, but not quite so ugly as that! Look at FaitalPro 8HX200 or Radian 5208C or BMS12C362. Their FRs aren't exactly pretty but they tame a lot more easily than these big coaxes. Common wisdom is to make the smaller coax with a woofer and let the woofer do the heavy lifting down low.
 
nc535 said:
And I do expect it, but not quite so ugly as that! Look at FaitalPro 8HX200 or Radian 5208C or BMS12C362. Their FRs aren't exactly pretty but they tame a lot more easily than these big coaxes. Common wisdom is to make the smaller coax with a woofer and let the woofer do the heavy lifting down low.
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They are not triaxials nor do they have a horn installed. A lot of the bad stuff is due to the horn. If you look at the DCX464 frequency response alone, it’s a lot smoother. Look at the BMS triaxials, they are also a hot mess.

These things are just not easy to work with and not easy to get right, but I’ve seen a few examples of wedges using these with an impressively linear frequency response. Certainly usable for home HiFi if you can stand the looks and size ;)
 
that is a good point about the bad stuff being due to the horn. I saw that myself when I was looking for a coax driver. not only does the horn mouth not have much of a termination but the woofer output has to diffract around the horn and MF horn output can bend around behind the horn and reflect off the woofer cone causing combing ripple. Perhaps that is why it's crazy to consider these. Better off using a coaxial without a horn, like one of the ones I listed, with a separate woofer for the low end.

You would think that if a manufacturer had a driver with such ugly FRs, which was much better viewed from off axis or which could be cleaned up with the right crossover, he would show that somehow in his data sheet or marketing material.
 
nc535 said:
You would think that if a manufacturer had a driver with such ugly FRs, which was much better viewed from off axis or which could be cleaned up with the right crossover, he would show that somehow in his data sheet or marketing material
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That isn’t usually done with PA chassis. But you’re in luck, because B&C has a kit for the 18” version that shows what is possible:
IMG_9840.jpeg

That’s with a hybrid crossover, making it a 2-way active speaker.

I also know that even the 2-ways like the BMS can perform way better than the datasheet with some care. I think you can find this a few pages back :)

As for the horn, possibly one could employ a similar setup to the top of the like KEF 3-way coaxial wall/ceiling speaker. It uses special materials to virtually extend the waveguide, and let the bass frequencies through at the same time. That should clean up the response quite a lot.

These big triaxials still intrigue me. Maybe at some point I’ll pull the trigger on a pair…
 
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well the 18"' FR looks much better and the application note is fairly comprehensive. The FR is impressively flat but the directionality anomaly at 1 khz concerns me. Its likely where the waveguide loses pattern control but if so, what narrows the response lower down? I've often thought the same thing - that one could/should do something to extend or better terminate the waveguide but I'm not willing to spend the money required to try ideas out. I don't want a box as big and wide as that anyway. I think Tom Danley had the right idea - seal off the opening between the woofer cone and the waveguide and then poke holes in the waveguide for the bass to enter. He does that with much smaller coax's though.
 
nc535 said:
He does that with much smaller coax's though.
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Not quite. The B&C uses a coaxial compression driver, where Danlay uses a 5.5 to 6.5” coaxial, or even no coaxial at all (1” CD and a series of smaller drivers). These all have slightly different trade-offs. The bass of a Danley system consist of just normal woofers through the horn itself. This indeed reduces edge diffraction artifacts significantly.

You could probably drill some holes in the horn for the woofer and get something similar to the Danley setup, then close up the area between woofer and horn. There is just no way back ;)
nc535 said:
I'm not willing to spend the money required to try ideas out
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Yeah, that is exactly the major issue here. It takes time and significant effort to get this working properly.
 
I was talking about Danley's use of coaxes. That might not work with an 18" coax because of cavity resonances. But the 18" crosses much lower and you could stuff the cavity, so maybe.

I actually designed and built a CD plus small woofers synergy horn back in the day. It was supported by a 15" woofer below so I would not have to have large bandpass ports in the horn itself. I can't say how much this helped because being a corner horn, there was no way I could get take good polars for it in my house, no usable corners outside, and the bass cab was too heavy for me to move by myself anyway.

1739111175678.png
 
ai1 said:
766EUR for 18HTX100
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Yes, it's an interesting chassis with some show values for those interested in technology, but like the BMS Triaxials, it wouldn't be my first choice for power hi-fi.
Many tuning problems, a horn that is too large for the cone loudspeaker underneath, a horn that is too small for the flange-mounted coaxial compression driver.
The 18-inch bass is also supposed to take over parts of the midrange and its ThieleSmall parameters do not allow a really low tuning.
To summarize: Too many compromises.
 
somebody did some speakers with those beast ? i was planning of doing something and i like the idea
 
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