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Old 4th November 2008, 07:50 PM   #11
cotdt is offline cotdt  United States
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Originally posted by Ryan_Mc
Sorry for the double post but I'm still under moderation (new member) so I can't go back and edit my previous post, but here is an example of the 'complex' xover networks I was talking about.
I had a good laugh when I saw where that link lead to. Zaph's ZD5 uses a relatively simple crossover with few parts. I trust that you've not seen the ZDT3.5's at the same website (which is itself relatively simple design for a 3-way)?

Active crossovers have even more parts and take a lot longer to make. Building an active crossover is basically like building a complete amplifier, with power supply, casing, input/output jacks, etc.
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Old 5th November 2008, 02:16 AM   #12
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I think that the important thing to remember is that no matter how you implment your XO, active or passive, to get the same sound, the XO transfer functions have to match. So for example, using the Zaph design pointed to earlier, you would have to match these transfer functions in your active XO plus imlement active delay to get the same frequency response that Zaph got.

You will note, those are not textbook slopes.

Active and passive XOs each have their own set of benefits and drawbacks. It is up to the designer to decide which provides the most bang for the buck for each design.

Good luck

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Old 5th November 2008, 02:41 AM   #13
Ryan_Mc is offline Ryan_Mc  Canada
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I agree getting the same transfer function could be a bugger doing it all actively. Op-amp filters can perform all the functions of caps/resistors/inductors so yes it can be done but is it worth it. Usually you can kill two or more birds with one stone, for instance a notch filter can be done with one op-amp and high and low frequency crossover points as well as Q and gain can all be adjusted on the fly by pots (I believe that particular function is called a parametric EQ).

I'm not trying to push the actives BTW, eventhough it might sound like it. I like cotdt's idea (and it seems yours) to mix and match passive and active based on the particular situation.

It's looking like this build will require minimal xovers anyway as the more I think about the full range 4.5" the more I like it. I still have some time to decide until I build my amps though.

Thanks for all the info,
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Old 5th November 2008, 02:56 AM   #14
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Originally posted by djarchow
I think that the important thing to remember is that no matter how you implment your XO, active or passive, to get the same sound...
I'd love to know if this is possible (getting the same sound). The passive XO interacts with the driver impedance, which actually changes a fair amount depending on the excursion and voice coil temperature. It would be interesting to find out how much of this variation is audible. With an active crossover, these driver variations are isolated by the amplifier, so changes in impedance with cone movement and voice coil heating shouldn't affect the output.

Some of the curves in the Klippel documentation show a substantial change in driver impedance with cone position and heating. I think it would be fun to set up a good A/B test that compared active and passive crossovers at different listening levels to see if the impedance change and the interaction with the other XO components is noticeable...and what does it sound like..?
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Old 5th November 2008, 03:31 AM   #15
cotdt is offline cotdt  United States
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At low crossover points under extreme temperature variations, passive crossover points would vary a bit. This is a moot point though, since the woofer's T/S parameters would change so much that performance would be degraded no matter whether you use active or passive.

In my experience, with decent parts passive and active sound the same. It's all about which is more convenient. Active crossovers are affected by choice of opamp and quality of its PSU while passive crossovers are affected by choice of capacitor, though neither makes that big of a difference. It's unclear whether the choice of capacitors used in active crossovers makes a sonic difference, I've always used good ones so I wouldn't know. Choice of inductor in passive crossovers make zero sonic difference.

Active crossovers are useful in dipoles and adding things like Linkwitz Transform. Those are not generally useful in 2-ways, so you probably won't be needing active.
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