Crazy PA Coaxials for Hifi

[Geert]

So, looks like @Juhazi has been quite busy the past few weeks with a crazy PA coax project, and he didn't tell us

That's unacceptable

Interesting project indeed. And I'm not surprised he ran into an issue with interference between the horn and the woofer cone. I said it before, all speakers are a compromise, but PA speakers often prioritize efficiency (loudness) and allow a higher compromise on the level of sound quality. I love coaxials, but they're easier said than done.

 

[voodooless]

That's unacceptable

Absolutely

Interesting project indeed. And I'm not surprised he ran into an issue with interference between the horn and the woofer cone.

Nobody should be, it's right there in the datasheet I am however surprised that you can solve the issue mostly with a waveguide extension. That suddenly removes quite a bit of resistance to these horned coaxes.

I'd still like to see a multitone comparison between horned and non-horned coax though. That should show if it's really worth all the trouble. And then there is the narrower directivity: horn coaxes offer generally 50~70 deg, while non-horn coaxes do 80~100 deg. Also due to the larger cone, the non-horn coax can be crossed lower (if the CD can take it).

 

[Plcamp]

Also due to the larger cone, the non-horn coax can be crossed lower (if the CD can take it).

Crazy idea, but could the horn be smoothly extended to baffle edge with ‘co-entry’ holes in it to support woofer output?

 

[voodooless]

Crazy idea, but could the horn be smoothly extended to baffle edge with ‘co-entry’ holes in it to support woofer output?

That isn't very crazy. You could just close off the whole woofer by extending the horn, and then making holes in the sides somewhere near the throat. This does have quite a few caveats though:
- The holes will create a bandpass. You won't be able to use the unit in a 2-way anymore unless you can place them strategically in such a wat that it still works out. It's not easy to test this out without destroying the horn.
- The cavity behind the horn is probably too large to make the bandpass holes work properly. You may have to 3D print some filler to make it all fit quite tight.
- The rear chamber generally should be quite small to give the thing the proper bandwidth.

Danley actually did something like that with a smaller BMS coax:

As you can see, this is also a 3-way horn.

 

[Plcamp]

Another more crazy idea is the extension of the horn as above, except the extension is done with high frequency absorptive material like felt. If a material were relatively transparent at LF and semi transparent at HF, you might extend tweeter performance to lower frequency while also attenuating problems associated with the gap between horn and woofer cone?

My crazy ideas are not, btw, anticipating using the coax for bass…but if a coax could support 300 hz up, I would be happy.

 

[voodooless]

Another more crazy idea is the extension of the horn as above, except the extension is done with high frequency absorptive material like felt. If a material were relatively transparent at LF and semi transparent at HF, you might extend tweeter performance to lower frequency while also attenuating problems associated with the gap between horn and woofer cone?

My crazy ideas are not, btw, anticipating using the coax for bass…but if a coax could support 300 hz up, I would be happy.

KEF did something similar:

https://images.salsify.com/image/upload/s--uWC_uPLW--/ccrgp5pvdz9o64mcb9kj.pdf

 

[voodooless]

Looks like we may have a new contender for the top crown of Crazy PA Coaxials:

18HTX100 Triaxials - B&C Speakers

100 dB (LF), 110 dB (MF/HF) sensitivity, 1600 W continuous program power capacity, 60°x40° nominal coverage, 44 - 18000 Hz response, FEA optimized horn flare for improved acoustic loading and controlled coverage, Double silicone spider with optimized compliance, Aluminium demodulating ring for...

www.bcspeakers.com

They will set you back € 809/piece if you buy two. Not to bad if you consider the cost of the coaxial tweeter and the horn alone.

 

[voodooless]

So this little wonder can be put in a nice reflex 120L box and will do up to 110 dB at 20 Hz with the appropriate tuning. It will need some DSP to flatten the response that way. It will also do 104 dB in a closed box of the same size, will need even more DSP boost, though.

For parties, you'd probably want to opt for some higher tuning, giving you 124 dB at 50 Hz and up from a single speaker

 

[SomeDude]

The megalomaniac in me wants to pair it with two 18" subs....each side.

 

[fpitas]

Is the Kef coaxial not in the running here?

 

[tomtoo]

Is the Kef coaxial not in the running here?

No its about crazy. Something like a 21inch with a 400Hz horn.

 

[voodooless]

Is the Kef coaxial not in the running here?

I guess that will depend on the criteria It won't win an SPL battle with the B&C monster.

It will however probably be more linear. THD? Who knows... IMD, my guess is the B&C will win.

 

[fpitas]

No its about crazy. Something like a 21inch with a 400Hz horn.

Well, alright then!

 

[fpitas]

I guess that will depend on the criteria It won't win an SPL battle with the B&C monster.

It will however probably be more linear. THD? Who knows... IMD, my guess is the B&C will win.

Probably true. I'm a fan of politeness in a speaker, but I think I'm at the wrong party for that.

 

[Steven Holt]

It will however probably be more linear.

Now I'm curious. Are you saying that there is an inverse relationship between linearity and driver size? Many people claim that the SQ of the Kef Q150 is better than the Q350. Could this be the reason?

 

[voodooless]

Now I'm curious. Are you saying that there is an inverse relationship between linearity and driver size? Many people claim that the SQ of the Kef Q150 is better than the Q350. Could this be the reason?

No I’m not. It’s just that we’ve seen the white paper of the KEF 3-way coax, and you can also look at the B&C datasheet. Clearly the KEF is more linear. Driver size has little to do with that. If anything, the horn makes things a lot more difficult. The woofer/horn integration will be quite tricky to get right.

Another thing the B&C is better at: pattern control. The 18” woofer will hold until about 300~400Hz.

 

[Steven Holt]

Thank you for the clarification, I understand better now.

 

[Plcamp]

Can I buy a new KEF coaxial driver anywhere? Or is it only online used ones?

 

[mhardy6647]

Well, alright then!

Looks like we've come to the right place!

 

[fpitas]

Can I buy a new KEF coaxial driver anywhere? Or is it only online used ones?

I've seen them sold as ceiling speakers, of all things. Maybe someone can say if they really are the same.