passive xover from dcx2496 settings?

[1darrely]

Hello,

I've been lurking here for some time now learning as much as I can about speaker building. I've built Zaph's Seas L18/27TBFCG system and a subwoofer and have been pleased with the results. Anyway, I've been playing with a dcx2496 in a 2-way system using the RS150 midwoofer and experimenting with various tweeters. My question is, once I am satisfied with the settings on the dcx2496, what would it take to use those settings to design a passive crossover that will duplicate them? Thanks for any help you can provide.

darrel

[JonMarsh]

Well, one reliable way that occurs to me is to enter the settings in a design program like LspCAD or SoundEasy that supports emulating that crossover, note the transfer function of the DCX2496, then develop a passive crossover which accomplishes the same thing using that program. OTOH, if your settings are fairly simple on the DCX2496, it may be easier than that, but that's how I'd approach the problem. I've considered getting a DCX2496 for prototyping design just that way, but when availability dried up due to the chip availability, that idea went out the window.

[cjd]

What tweeter?

You can always just go build one of the existing 2-ways with the RS150.

Passive gives you a different set of tricks compared to a DCX - I might use digital to assess driver compatibility, crossover points, and the like, but I would probably always start (mostly) from scratch... sure, I might shoot for an 8th order slope, but I'd go C-E passive, so... really, take the slopes, use them as a target, as Jon has already mentioned.

C

[1darrely]

Thanks for the replies. What does "note the transfer function of the dcx2496" mean? That one's way over my head. Assuming my settings are fairly simple, what would be the easier route? I'm currently trying the North D2506, but have played with the Vifa D26NC55, and have the Seas 27TDFC waiting their turn. As for building a proven design, I find it somewhat risky without having heard the design. I've found that a flat frequency response just doesn't work for me, as I prefer a substantial laid back sound. That's why I selected Zaph's design. He provided response shaping options that I ended up using to attenuate the upper midrange, similar to a bbc dip.

darrel

[Dennis H]

Transfer function is just a graph of the voltage applied to the drivers at different frequencies.

[1darrely]

Thanks Dennis. Excuse my newbieness, but how does one go about developing such a graph?

darrel

[Dennis H]

Like Jon said, you need measurement and crossover simulation software. You also need a measurement mic and preamp to really do the whole thing right. I guess the short version is you need a bunch of gear ($) and time to learn how to use it if you want to design your own passive crossovers.

[cjd]

I think that it comes down to the fact that you STILL need to know what you're doing to design a passive crossover. It's unlikely you can find a way to just plug-n-play. There's a bit to learn before worrying about target transfer functions, mostly because targets often are made to be missed in this case. Or, not hit dead on.

C

[1darrely]

Okay, there's no way around purchasing SoundEasy or LspCAD. I have an ECM8000 and MobilePre USB which I used to tune my truck's audio system. So if I decide to make the commitment to buy and learn one of the mentioned software, is there any other gear that I'll need? Thanks for all the advice.

darrel

[cjd]

Oh, you definitely do NOT need Soundeasy or LSPCad. You can use Speaker Workshop.

It works, and it works well. But it's not to the level of either of the paid software options you mention. If you're not sure about all this, however, it may be a worthwhile place to start...

C

[JonMarsh]

The problem, Chris, is going from his DCX2496 settings to knowing exactly what the target transfer function is from those settings. Does Speaker Workshop have DCX2496 emulation support now? I haven't looked at it for ages. If he knew his transfer function, then he could use pretty much anyone's design software that modles the crososver and driver impedance accurately.

[cjd]

Nah, it doesn't Jon.

I was simply going from the angle of "get measurements, build crossovers" - and the "use it as a suggestion, not a target" philosophy which wouldn't bother trying to import and target. Well, and the FREE part.

Also, the excellent tools at the FRD consortium may help - for crossover design in particular, the PCD spreadsheet may be the best bet alongside measurements taken from wherever.

C

[Dennis H]

Yeah, I think he could just measure the output of the DCX to get the transfer function.

I'm not sure I trust LspCAD's DCX emulator anyway, at least the shelving filters. It sets the frequency to halfway between the upper and lower corners and I don't think the Behringer works like that once you get past a certain gain/cut level. The frequency should be the 3dB point of either the upper or lower corner depending on whether you choose high shelving or low shelving.

[1darrely]

So, is it safe to say that if I get the basic version of LspCAD; I would have the capability to measure the transfer function myself or use the built in dcx2496 component, and LspCAD would spit out the crossover design and allow the emulation of that design? Thanks for the help guys, I appreciate it.

darrel

[Doug Lockwood]

Okay, there's no way around purchasing SoundEasy or LspCAD.

I have v10 of Soundeasy. it doesn't "do" emulation the way I expected. I expected it would translate the passive components into DCX xfer functions.
Soundeasy will do exactly that with a soundcard.
With the DCX, you build active filter elements and can see the transfer function with and without the driver.
Or that's the theory. :roll:
I never got the active elements to play nice. Tomorrow is another day. :lol:
For my OB project, I measured the drivers, plotted out the result, than manually inputted the XO into the DCX with the graphical console tool. Crude, but effective. :T

Doug

[Paul H]

So, is it safe to say that if I get the basic version of LspCAD; I would have the capability to measure the transfer function myself or use the built in dcx2496 component, and LspCAD would spit out the crossover design and allow the emulation of that design? Thanks for the help guys, I appreciate it.

darrel

Short answer is no.

You have to know and understand crossover design, to be able to set up the various components and general configuration in the crossover. The software can then optimize these components to a certain transfer function - but it isn't smart enough to do it from scratch.

One analogy is the use of Autocad to draw full plans for a house - if you know how to design a home Autocad is a powerful tool to assist in the design/drafting process - but it can't design your home for you.

[1darrely]

Thanks Paul. I guess I was expecting too much from LspCAD. :

darrel