Which 8" coaxial ?

[David dP]

Hi everyone,

I'm new here (been lurking for quite some years though), but I've been building my own speakers for almost 20 years (God, can it really be that long ?). Unfortunately, I'm not very familiar with the high sensitivity side of hifi. That's the reason why I'm asking for you guys' opinions.

These days, I'm starting thinking about a new project : "Multi-role" ultra-compact active speakers, mostly to be used as PA floor monitors, but with a real hifi quality to them.

In other words, I'd like to have at the same time : high input power and high sensitivity, good high/lows integration, low distortion, similar distortion behavior at all power and frequencies, even dispersion, blablabla, etc...

Since I have to start somewhere, the first design choice is to go with an 8" coaxial per speaker.

Now, there are quite some 8" coaxials out there, so I'd appreciate any kind of opinions, info, reviews, comparisons etc...

Here's my preliminary list, in alphabetical order :

- 18sound 8CX400F
- B&C 8CXN51
- Beyma 8XC20
- Beyma 8CXN51
- BMS 8CN552
- Ciare NDCX8-1.4
- Radian 5208C

I did a search in the forum, and saw that some of these drivers have been used by forumites. But since I couldn't find a thread that would aim at compiling this info, I figured I could add this one to the wealth of info here.

BTW, I'm thinking of using Hypex AS2.400 modules, any opinion on those ?

So have at it, and thanks in advance for your help !

Cheers,
David

[dirkwright]

You just have to run some software simulations on each one to get an idea of what you're dealing with. I've done that with the B&C 8CX21 and it doesn't go down very low....

[David dP]

Thanks Dirk ! I'm definitely doing that ! And the amp module's DSP allows me to extend the low end a little bit if needed.

But beyond the purely technical side of choosing the driver, there's the whole subjective thing of "does it sound good or not ?"... Hence my cry for help ! ;-)

[dirkwright]

Originally Posted by David dP

Thanks Dirk ! I'm definitely doing that ! And the amp module's DSP allows me to extend the low end a little bit if needed.

But beyond the purely technical side of choosing the driver, there's the whole subjective thing of "does it sound good or not ?"... Hence my cry for help ! ;-)

I would try to find one that has a separate horn for the HF compression driver. One thing that happens with these coaxials is that the woofer modulates the tweeter output unless there's a separate horn for it. You can see this in the ripple for the tweeter response.

[jerome69]

Salut David,
The drivesr you have selected are done for mid, no bass...

You can also see with Musikit in lyon Bienvenue sur la page des News MUSIKIT
SEAS makes for them a 8" Coaxial...
8" coaxial paper - 7" coaxial TPX - 7" coaxial magnesium

look like but it is not the same cone


Cheers.

[fabel]

Hey David,

one driver that is on my mind is this: FaitalPRO - Professional Loudspeakers Made in Italy

If the measurement on the side is reliable it is one of the Pro drivers that goes nearly flat in both directions low and high to its possible crossover point.

G F

[RockLeeEV]

Originally Posted by dirkwright

I would try to find one that has a separate horn for the HF compression driver. One thing that happens with these coaxials is that the woofer modulates the tweeter output unless there's a separate horn for it. You can see this in the ripple for the tweeter response.

I disagree. You want the coaxial to be the horn, because it gives smooth polar response. There's some tweeter response ripple but you just need to work a bit harder, and an active crossover makes a HUGE difference!

The key with these 8" coax mids is to use them in 3-ways, not 2-ways. Cross them over around 250-300hz to minimize the mid cone movement. This takes away woofer cone modulation of the tweeter. This is what Mark Seaton does with his custom coax in the Seaton catalyst and Jeff Permanian does with the JTR Triple 8. I believe Mark has worked with the B&C 8CXT before and was reasonably happy with it. It's also what KEF does with the BLADE (btw, if you can lose some sensitivity, the KEF Magnesium Uni-Q is probably the nicest measuring coax out there that doesn't cost 4k/pr) and what TAD does with the Reference One (that 4k/pr coax I was talking about) I'm personally looking at the Radian unit myself.

If you wanna keep it a 2-way, I recommend going to a 12" or 15" coax with a bigger compression tweeter. Radian and Tannoy have two such options.

[alspe]

Originally Posted by RockLeeEV

The key with these 8" coax mids is to use them in 3-ways, not 2-ways. Cross them over around 250-300hz to minimize the mid cone movement. This takes away woofer cone modulation of the tweeter. This is what Mark Seaton does with his custom coax in the Seaton catalyst and Jeff Permanian does with the JTR Triple 8. I believe Mark has worked with the B&C 8CXT before and was reasonably happy with it.

Interesting idea. What do you think, is 6,5" or 8" coax better if 3-way is going to be that small that woofer has (lot) less sensitivity? Say 8" woofer at 40 l box + coax, xo at 300 Hz.

[RockLeeEV]

Originally Posted by alspe

Interesting idea. What do you think, is 6,5" or 8" coax better if 3-way is going to be that small that woofer has (lot) less sensitivity? Say 8" woofer at 40 l box + coax, xo at 300 Hz.

It's tough to say, and I suppose it comes down to how narrow you want the directivity to be, and how capable a tweeter you're using.


Radian's "ultimate" coax is a 15" woofer, kind of like Geddes' Summa to an extent. It's so capable that you can cross actively it to subwoofers around 80hz and never have to worry about modulation of the treble, and the added bonus is directivity control down to 1khz for best imaging. Radian and Tannoy have some 12" coaxes too. I know one fellow around here uses the Tannoy coaxial in a very low diffraction box.

The problem with both of the above is that the compression tweeters used are 1.5" so you lose a bit of top end.

Seaton and JTR both use 8" coaxials and 1" compression tweeters. I suspect this is a good balance between output, narrow directivity, and size. Here is a picture of what the Catalyst looks like - that's two 12" acoustic elegance woofers and an 8" coax... and it still needs multiple subwoofers!!

The $75000/pr TAD Reference One uses a 6.5" beryllium coaxial mated to a pair of 10" woofers. I believe this is getting into traditional tweeters rather than pro sound compression tweeters. I suspect it's the best sounding, but have fun sourcing that $4000/pr coaxial driver. Dispersion will be a bit higher but it's the first one to use a metal cone rather than a paper cone, and it's safe to say that it's probably pistonic over its entire passband, which is never a garuntee with treated paper cones although i'm unsure of the audibility of that.

The $40000/pr KEF Blade (sensitivity is around 92db i think) and $9000/pr Pioneer S1-EX both use 5.25" magnesium coaxials in 3-ways. No doubt they sound pretty good but at this point you really start to get into "wide directivity" rather than narrow directivity. The Pioneer is really expensive but i believe the KEF Uni-Q can be obtained if you contact that. These are traditional drivers like I said, not pro sound tweeters and ultra high power handling mids.

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.

If I could just get me the TAD coaxial i'd be in heaven though.

remember that if the 5" driver is designed to NOT try to reproduce 60hz it can be reasonably high sensitivity for a 3-way.

[jerome69]

Originally Posted by David dP

Thanks Dirk ! I'm definitely doing that ! And the amp module's DSP allows me to extend the low end a little bit if needed.

Only if you make a closed box but my experiment has shown a 8" extended in the bass doesn't sound good. For PA application you don't need too much bass, a BR box is enough. But for HiFi you will need bass.

Originally Posted by David dP

But beyond the purely technical side of choosing the driver, there's the whole subjective thing of "does it sound good or not ?"... Hence my cry for help ! ;-)

Hard to say ! PA doesn't pay attention to quality but to power handling.
We can have good surprising drivers but on the paper hard to tell.
I think if you want a PA coaxial speaker, forget HiFi and choose what you want.
The address i gave you is a HiFi speaker but power handling is 80W instead 200W, sensitivity 90dB but can goes as low as 40Hz in 40L .