Big Blue

[jack_bouska]

I ordered a Behringer DCX2496 digital crossover yesterday so I can hook these babies up to some amps that I am more familiar with and tune in the response a little better. I’ll have to hold off on a more expensive crossover for now.
When it arrives I plan on using the digital link from the cd player and setting up some sort of 6-way volume control between the crossover and the amps. I don’t know exactly what this will look like just yet, probably 3 stereo analog pots connected with gears and a small chain or something.
Anyone done anything similar?

I built up a 12 gang log pot by dismantling 12 dual potentiometers and re-assembling the pieces so that they all connect together to form a single very long multi-ganged potentiometer. Tracking is reasonable, but not perfect. A six gang version would be better. Buy extra pots, and match the tracks using an ohm meter, then assemble matching carbon tracks as stereo pairs.

I use this beast to adjust the output volume of a pair of DCX2496's, configured as dual 5-way crossovers. See attached images. I don't have the manufacturer make and stock number, but I'll look it up when I get home tonight. - Jack Bouska

[scorpio]

Selectronic in France does a kit for similar purpose, have a look at:

http://www.selectronic.fr/audiophiles.asp

Caution, it's all in French...

They also have an interesting page on all sorts of other mods for the 2496, including power supply etc...

Sorry, can't write a translation, there's too much info.

Cheers,

[scorpio]

Blaaah, my mistake, go at the bottom corner of the page I sent the link, they have an international page with an english fact sheet, sorry it's late in the day for me already...

[jack_bouska]

I don't have the manufacturer make and stock number, but I'll look it up when I get home tonight. - Jack Bouska

I dug out a sample of one of the dual gang pots that I am using, and had a look at the manufacturers name, they are listed as NMEG (see photo below).

These are fairly expensive, see maplins catalogue:
http://www.maplin.co.uk/Search.aspx?criteria=FX09K&DOY=8m11
However they provide good front to back tracking when ganged together in large lengths.

For a simpler, and less expensive option, try looking for potentiometers which allow adjustment via access at the back of the pot, using either a flat blade screwdriver or hex shaped Allen-key recess. You can then build a six channel volume control by ganging together three stereo pots, by shaping two of the front spindles to fit into the back of the preceding pot. See example in photo below. Front to back tracking is not as good as the nmeg option above, but a little dab of epoxy helps fill the gaps and form a tighter unison.

Another (much more expensive) option is to use switched volume controls, like the CT2 six gang version from DACT http://www.dact.com/html/attenuators.html which will set you back a few hundred dollars (almost as much as the DCX!), so buying a few dollars worth of stereo log pots looks like a much more economical approach.

Jack Bouska

[John W]

Thanks for the info. This looks like a good solution. I'll check out a couple sources today and see what I can find.

[John W]

I got the new Behringer crossover connected up this weekend. Hooking up the speakers through this crossover to a trio of mosfet home-built amps made a big difference in the sound. Much better.
The volume control is three dual pots connected side-by-side with ribbed knobs and belts. I think connecting them front to back would be a better solution, but I didn’t want to wait for mail-order and was able to get work this up from locally available parts.
So far, the crossover is working out quite nicely. The software is fairly intuitive and sound is great. The horns are very natural sounding, but even after equalizing them flat as best I could, I found the 2445s a little harsh. Eventually I swapped in a pair of aluminum diaphragm 2440s which is a big improvement.
Also the initial tuning of the ports was 28hz. This was a little low and boomy for the woofers, so I swapped in a couple shorter ports bringing the tuning up to about 32hz. Anyway, I’m not done tweaking yet.
Here are a couple shots of the setup and the equalizing on the drivers. The response is fairly flat now.

[jack_bouska]

The horns are very natural sounding, but even after equalizing them flat as best I could, I found the 2445s a little harsh. Eventually I swapped in a pair of aluminum diaphragm 2440s which is a big improvement.
(snip)
Here are a couple shots of the setup and the equalizing on the drivers. The response is fairly flat now.

What's the vertical & horizontal scales on the green RTA display? (Hz and dB/div)

On axis?
how far from the boxes?
how do the curves look off axis?

as mentioned in an earlier post, the 10kHz passive xover to the cat's eye is probably too high and not steep enough to suppress the diaphram breakup on the 2445's. Aluminum has more internal damping compared to titanium, and the 2440 phase plug might also suppress some of the breakup above 10k

[John W]

The RTA is Behringer too, an 8024 in 1db mode. I think there is an 8db spread vertically between the grid lines.
You can just make out the horizontal scale if you look real close at the picture. Roughly the first 19 bars cover 20hz to 1.25k, the next 10 bars cover the range of the horn 1.2k to 10k, then the last three the tweeter. I think that either the pink noise generator or measurement setup is missing in the tweeter region. I can make adjustments and hear the difference, but can't seem to get the top bars level.

This measurement is taken about 2/3 of the speaker height vertically and about 4 feet from the front, on axis. I also took some measurements from the actual listening position and did a little more tweaking there.
I missed doing the off axis measurements. I'll have to set things up and try that part again.

[John W]

as mentioned in an earlier post, the 10kHz passive xover to the cat's eye is probably too high and not steep enough to suppress the diaphram breakup on the 2445's. Aluminum has more internal damping compared to titanium, and the 2440 phase plug might also suppress some of the breakup above 10k

Yes, this could very well be the case.

[John W]

I turned a pair of new horns for the big speakers for use with a pair of 1.5 in 2435HPL drivers. After playing around with a few different designs using the Hornresp program I settled on the design below.
http://www.users.bigpond.com/dmcbean/

The program isn’t the most user friendly, and I had to estimate a few of the parameters, still once you learn the basic steps it allows you to easily calculate contours for quite a few types of horns.

I needed the design to fit the existing hole, and terminate flush with edge of the cabinet. The design starts off as an oblate spheroidal contour at 700 hz and transitions into single spherical to angle it around flush.
The sound really nice, very natural and uncolored. The 2435HPL is fantastic, super detail and transparency.

[John W]

Here is a plot of the horn response in the cabinet on axis about 3 feet from the mouth, and a plot of the equalized response of the whole speakers.

[Robh3606]

Very nice John! Glad to see you are enjoying your drivers! Those horns look great!!!

Rob

[Mr. Widget]

Very cool John.... I am once again impressed. Keep up the great work!!


Widget

[edgewound]

Wow, John.

Your craftsmanship is absolutely first rate.

[pangea]

IMHO, DON'T.
On paper and in use this is an amazing piece of gear for "Home" use. BUT, I have owned three of them and every one has the habit of making an intermittent "Sizzling Bacon" sound when I think it looses a ground due to piss poor construction or some other reason beyond my capacity to under stand. I guess when you steal someone elses design and built it cheaply you miss a few things. It does have PEQ, Limiter, Auto Time Alignment/Phase setup among other functions.

Zilch has one now, maybe he can shine some light here.

I ended up with a YAMAHA D2040 4 way digital that sounds good. It has no where near the bells and whistles as the DCX 2496 but is clean and solidly built.

I have two of those Ultradrives and both of them have that same "Sizzling Bacon" problem, one of them was sent back to Germany but came back with the same problem, so I haven't bothered sending the other one back.

Behringer still pretend there is no problem with them, although I have heard people complain all around the world.

Right now I have a dbx Driverack 260 at home and this one is far better. It even does what the Behringer Ultracurve does, so the extra cost is well spent IMHO.

/Roland