B&C 12CX/8 coax

[MikeS]

I may have bought a pair of these, not really certain yet, but rather sure.

http://www.bcspeakers.com/download/prodotti/PDF/more/153.pdf

Don't know why, I don't have any sort of way to build enclosures. They guy I got them from moved away and sold his stuff.....
Other than throwing them in existing enclosures of various sizes.

I can either buy the crossover networks or hammer him for the diagram to cobble up my own.

He says he likes them. The 54 fs is kinda high.....maybe a larger box or just run the woofers good and hard and loosen the suspension up a bit.

I do like the point source kinda sound with co-axials.

BTW, they are blowing these out on eBay at around 200 a pair....Not a bad price for a good quality italian made coaxial.

Mike

[MikeS]

My audio buddy Dan posted on Joenet about the B&C 12CX/B coax. Now the guy is sold out on them.
I'm looking forward with regards to listening to these........

[95Honda]

I bet they would sound pretty good.

One thing maybe you could do to get a little more low end out of them is add a little mass to the cone to decrease Fs. Just make up for the slight loss of efficency in the tweeter circuit of the crossover, it would probably only be a db or so...

A buddy of mine bought a bunch of Carboneau (I think that is how you spell it) woofers we were playing around with in the early 90's. Paper cone, rubber suuround, 40 Oz mag, about 9mm of xmax... Pretty much run of the mill for the time. We were measuring them using IMP. One thing we noticed was that thier Fs was a little high (30Hz) for what we wanted, and modeling showed lowering the Fs a little would help. We painted the cones with Varethane liquid plastic... It dropped the Fs about 4-5Hz, made a neglidgable efficiency difference and stiffened up the cone, they measured better... And looked better... Just an idea...

[MikeS]

Here's a schematic of the XO-2 network for 12CXT and 12CX/B.

http://homepage.mac.com/planet10/forum/BnC-XO2-map.gif

I dunno about damping the cone....I understand where you are getting at with lowering fs by adding mass to the woofer cone. But it may be at a sacrifice to upper midrange frequencies, where it maybe can mess up the center frequency of the network.
The frequency range where it crosses over to the tweeter.

Maybe leave the tweeter unhooked, and drive the piss out of the woofer, and loosen up the suspension a bit, maybe that can help.
Or raise the qts and use a larger cabinet tuned lower than fs a bit. I do use use tube amplifiers.....I've had good effect using a semi-fullrange 10", with a fs of 50 Hz in a 3.5 foot volume box, tuned to 36-38 Hz or so.

They12CX/B's got sent today, so I better scrounge up the parts off PE or sumthin' for the networks.....

Mike

[95Honda]

I have a bunch of parts kicking around, let me know if you want some of them...

[MikeS]

Ok.......I have your phone #'s lying about here somewhere. If they are both still current......

[MikeS]

These B&C coax's showed up today.
Gotta love Fedex......I was at work at the time, so they the just set the box next to the porch and put a snow shovel over it.

Good thing nobody snarfed the box. I guess that excellent job of hiding it with a snow shovel worked...heh....

They look like decent built speakers. With shipping included, it comes out to $102.50 per driver. I don't think I could have done worse........

Mike

[MikeS]

My friend Dan found the XO-2 passive networks online for 45 bucks a pop plus roughly 15 bucks shipping.
He says the are quality made units with good parts for high power.
He did note no bi-polar capacitors used.

The B&C's are high power quality drivers, that retail at $269 each.
The networks retail at $78.

I doubt I could kludge up networks cheaper than that.

[MikeS]

Cool....I have a pair of baffles cut-out for 12 inches that the B&C's will fit.
I even still had the PVC ports.

I can mount one in a 3.5 foot homebrew cabinet to try out.

I have a aftermarket passive network to use with a center frequency at around 2.5-3kHz.

It's enough to get a half-assed take, I got plenty of Dacron polyfil to play with and hopefully don't have the ports cut too short.

See how it sounds.....

Mike

[MikeS]

Pay no heed to the lampcord wrapped around the crossover.....

[95Honda]

So, how do they sound?

I still have a bunch of parts if you want to tweak em'

[MikeS]

So, how do they sound?

I still have a bunch of parts if you want to tweak em'

I don't have the port tuning quite dialed-in. It may be too low, there is a peak at 70Hz.
I just rapped with Dan with regards of using a frequency generator and a VTVM to watch and determine the tuning point frequency, and ways to shortening the ports and beat down the peak.

He mentioned the tuning should be around 45-50Hz. I'm probably at 35-40Hz.
The bass is rather good and smooth with music considering the peak, but you can notice it. Little more work to go......

I am using a different crossover with a center frequency of around 2.5kHz, with the tweeter padded down, but the midrange and top-end sound really good.
The stereo image with a coaxial is like headphones, almost point source....

I like them so far for a intial start.

Dan Marshall is supposed to be getting the proper crossover networks for the 12CX/B. I'll ask him if there is any differences between the x-over network he has for 12CXT, and the 12CX/B network.
I would think the 12CX/B network has some sort of HF compensation for the compression driver tweeter.

If his new networks match the XO-2 schematic I posted, then I'll bring a diagram of the network and see what you can scrounge up.
Might save a few bucks, see what happens....

Mike

[MikeS]

Mike bummed me these nifty speaker breadboard crossover jigs, and some parts over last weekend.

I went ahead and copied the XO-2 network for the B&C 12CXT and 12CX/B with what parts Mike has, and what parts I had on hand.

For low pass, the stock network calls for 1.0 mh inductor in series. I have 1.8 mh Solen 14 awg hyper-litz wire air core inductors, Mike has 1.5 mh 12 or 14 awg solid wire Solen air core inductors....(I think they are Solen..)

I've been swapping between the two, and haven't determined which I liked best. I tried a solo Rockford Fosgate brand 1.0 mh iron core inductor, and it made the bass sound mushy and soft.

In the LCR trap, the stock network specs .30 mh, 10 uF for the cap, and a 1 ohm 20 watt resistor. I could not find a .30 millihenrie value, so I swapped between a .27 mh inductor, a .25 mh, and a .39 mh inductor.
I seemed to prefer the .39 mh value over the others, the other values sounded more thinish to my ears. The .39 mh made things sound fuller.

I'm using a Bennic 5% 9.9 uF 160 volt cap, with a Jantzen 1.0 uF bypass, and a 1 ohm 25 watt R.

For the high pass, I've managed to scrounge up 2.5 ohm input resistors. Spec is 2.7 ohms.
Then a Bennic 6.6 uF 5% 160 volt cap with a North Creek Harmony 0.22 uF bypass cap. These Harmonys are only plus or minus 10%, I thought they were tighter than that.....
X0-2 network spec is 6.8 uF. I'm damn close at 6.82 uF.
The inductor and resistor in parallel before the tweeter is specced at .20 mh, with a 1 ohm 20 watt resistor.
I'm using a Jantzen 18 awg .20 millihenrie air core inductor, with a 1 ohm 25 watt resistor.
I tried other values of chokes, .25 mh, .27 mh, and a .16 mh 18 awg Solen hyper-litz.
I think sticking around the same value is probably pretty critical here, because all the other inductors I tried sounded wretched.
I played with other values for the series cap in the tweeter circuit.

I tried a North Creek 6 uF 200 volt + or - 10% Crescendo cap, bypassed the Bennic 6.6 uF with a Aluminum Jensen 0.22 uf, even bypassed with a Russian military 0.47 uF Teflon capacitor.
I seem to prefer the 6.6 uF cap, bypassed with the North Creek 0.22 uF Harmony.
I think being a 12 db HP network, (with EQ) capacitor tolerance may come into play here.
The Bennic's are 5%.....all the other values and types I tried didn't sound as good. I still need to configure up the 6.8 uF value using other types of capacitors and see how it sounds.

Getting a proper crossover lashed up really made a major difference with these coax's.
These things sound like high fidelity now....everything I play sounds good....even the shittiest CD's sound pretty good. They flat romp with a 30 year old JVC SS 60 watt integrated amp, and sounds damn good as well.

Hell, they even get and boogie with a single-ended pentode connected 6BQ5 5 watt amp.
And listening with a 2A3 stereo SET amp is quite the magical stereo experience. 3.5 watts can do wonderful bass.....within it's working levels of course...

I couldn't see bothering with looking for vintage Altec, EV, or Tannoy coaxial drivers, unless you can come across them really cheap.
Mismatched drivers, magnet wear, cone/surround damage, higher impedances are all factors to consider.
Tannoys command big prices, so do the Altecs. I'd think these modern B&C coaxials will dance right along with a Tannoy 12" monitor gold. Maybe even best it....a helluva lot cheaper nonetheless.....

MikeS