Active v. passive crossovers

[Drew]

Somewhat recently I read an interesting statement by a member of this board regarding active crossovers. The gist of it was that he prefers to use passive crossovers. He didn't offer any explanation.

I've been building active XOs for a few years now and I prefer them for mainly one reason: convenience. It's so much easier to tweak a design by changing a few small resistors and caps and messing around with opamps rather than ordering and waiting for large components to arrive.

However, I'm open to the possibility that there is a better way. What advantages do passive XOs offer? The only one that I can think of is noise. It takes careful board layout to have a quiet active XO.

I guess the other advantage is amplification cost, which is what prompted this examination. I'm getting ready to buy some new amps and 6 vs. 2 is a big difference 8O I'll probably get another 6 channel setup to mess around with, but for the main rig...hmmm.

(anybody have any good amp recommendations?)

[ThomasW]

That particular person has also designed and built multiple VERY high-end active crossovers. So don't take everything he says literally.....:wink:

(anybody have any good amp recommendations?)

I have a pair of Ayre V-5xe's I like a lot... :B

[BobEllis]

Drew,

I agree with your reasoning for choosing active crossovers. For me it is easier to daisy chain active elements than figure out the effects of interaction of passive. However, there are some good free/low cost sims that make getting pretty darned close with a passive fairly easy once you learn how to use them. Speaker workshop for example.

As for your amp requirement, have you considered DIY? The Leach amp is an excellent sounding amp, despite its age. Boards are available from Professor Leach and there are several updated versions (using plastic output devices) available on the web.

Other options include a Krell KSA50 (or 100) clone or one of the Nelson Pass designs available at www.passdiy.com I have a slight preference for my Pass A75s (modified for increased output) over my Leach, although as summer approaches, I may go back to Leach amps due to the A75s class A heat load.

If you'd prefer to build a kit look for AKSA amps and Greg Ball's "Simple Killer Amp." I haven't heard either, but they are highly regarded.

[Drew]

As for your amp requirement, have you considered DIY?

Thanks for the reply, Bob. I have considered DIY, and I think that it would be fun to do, eventually. The issue is time - namely that I don't have any to speak of. Work is a bit nuts and what time I do have to spare I want to spend enjoying the music and not at my bench with a soldering iron...

[toolsresearch]

Passive v. Active

Of course the drawback with even well designed active crossovers is "complexity."

There are some things you get in exchange for that "complexity," though.

To equal multiple small amplifiers hardwired to a voice coil, you need BIG amps. If you compare apples to apples, cost is probably a wash. I think the test that was done (see Dickason for the citation) said that to equal a 50w and 30w amp you would need 250 watts into a passive crossover, but it's been 10 years since I read the paper and I'm sure the numbers are off. But, it's something like that. Multichannel amps are commonplace these days as well. Linkwitz (linkwitzlab.com) recommends ATI, some examples:

http://www.ati-amp.com/at6012.html

http://www.ati-amp.com/at1800.html

When you start factoring in 9 awg coils from North Creek to get your resistance down, extra channels of amplification start to look like good deal! I'm not convinced that the complexity argument is as good as it was ten years ago.

Furthermore, you pay a huge price for the reduced complexity of passive crossovers, since those are based on two assumptions:

1. Voice coils don't get hot
2. They don't move

Both are false, wickedly false even. If you try to compensate for non-linearities when the system is driven hard, you take on board non-linerities when coils are cool and lightly driven. The net result is that active systems scale better: turning up the volume doesn't cange the "sound." It just get's bigger. So if you want your volume control NOT to act as a tone control, you have to have an active set up. It will already act as a tone control plenty just thanks to our ears, without adding more problems to the stew.

Anyway, one could go on. If an application requires passive crossovers, make do. Otherwise, live it up.

Here is a well-informed discussion:

http://sound.westhost.com/biamp-vs-passive.htm

http://sound.westhost.com/bi-amp.htm

http://sound.westhost.com/bi-amp2.htm