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Old 21st December 2008, 07:34 AM   #1
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Default A couple of questions re: bi/tri amping, electronic crossovers

Hi Guys and girls.

I've been thinking of my next project. I have some drivers lying around and I'm going to sus up a box for them. I don't really know too much about them except thier size so I'm going to use an electronic cross over (crossover?) and tune them up that way. I know that is probably herasy but I figure if I use some pleasing proportions on the box and make it look nice I can always give them away as a present!

Bi amping/tri amping: Is this when you put an electronic cross over in between the source and the amp(s)? Then you run seperate channels to each driver?

Is there a benefit to separating the signal before the amp vs after? Because all things being the same, I think using one channel per driver is a lot of channels.

I'm thinking of putting the electronic cross overs in the boxes. I have some 8 inch speakers, some 4 inch speakers and some 1 inch silk tweeters somewhere.

Do electronic cross overs allow you to adjust the volume to each driver as well as cross over points? That would totlally negate the need for impedence matching.

I've seen a bunch of electronic cross overs on ebay from $20 on up to $80. Is one better than the other? Anyone care to discuss merits of a brand or type?

I'll take some photos of the drivers tomorrow and post them so you can see what I got and talk me down.

Thanks for your input.

Best regards,
Spencer
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Old 21st December 2008, 07:57 AM   #2
eplpwr is offline eplpwr  Sweden
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Default What Bi-/Tri-amping is

Hi!

For a very good explanation of what bi- and tri-amping is about, see:

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

... and ...

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

These two articles got be convinced, and when I heard the results later (after DIYing amps and x-overs for two years), it was the largest improvement in audio quality I've ever heard. I didn't even use expensive drivers or components, just "decent" stuff.
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Old 21st December 2008, 09:05 AM   #3
Francec is offline Francec  Australia
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I'll vouch for active crossovers and bi- tri- amping.
One speaker is actively bi-amped and the other passive, No guessing which sounds as if it has a towel draped over its front.

Frank
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Old 21st December 2008, 03:44 PM   #4
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I also prefer active. For main to sub XO it is the only way to go as inductors for an <80Hz XO are hard to source. Yes, it costs a bunch to get going but once you have 6-8 channels of amplification experimenting and/or new project becomes a matter of minor inexpensive tweaks.

Theoretically, active and passive crossovers with the same transfer function will sound identical. This doesn't consider the headroom improvement that Rod Elliot talks about in his article.

You can also go mixed mode. Active XO woofer to mid, and passive mid to tweeter. This would allow a 3 way with only 4 channels of amplificaiton.

It is smart to have a cap in series with the tweeter to protect it from DC on the amp's output. You could make this cap part of the XO or just make it big enough that it is a DC blocker. I cannot hear a difference with or without the cap (2 x 12 uf Axon) using Focal TC120 tweeters, so I left them in for peace of mind.

Most of the inexpensive ready made active XO's are pretty basic - textbook symmetric slopes and no eq, delay or baffle step compensation. If you are crossing at the baffle step you can use the level adjustment to compensate, but that limits you. Also, see Mark K's pages for the impact that this scheme has on power response.

If you want a relatively inexpensive full featured crossover, take a look at the Behringer DCX2496. I haven't used one but plenty of folks around here love theirs.

For DIY analog active crossovers, the best reference around is http://www.linkwitzlab.com/filters.htm Adding phase compensation to my XO (correcting for XO phase shift and mid/tweeter acoustic offset) made more difference than anything else. Transients suddenly became precisely focused. My teenage son even noticed the improvement without my pointing out I'd made a change.

It is possible to build an active crossover on perfboard, but it takes a lot of time and attention to detail.

Sorry, I don't have any XO boards leftover from the group buy. There were over 1,500 sold, so I bet if you ask in the thread there will be someone willing to part with the boards that they bought for the project that never happened.
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Old 21st December 2008, 04:16 PM   #5
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Quote:
Originally posted by BobEllis
If you want a relatively inexpensive full featured crossover, take a look at the Behringer DCX2496. I haven't used one but plenty of folks around here love theirs.
While i found this unit very versatile, the sound of the one i had was abysmal. I still want to try out a modifies one.

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Old 21st December 2008, 04:33 PM   #6
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Thank you for your responses Pelle, Frank, Bob, and Dave. The reading material is interesting if on the heavy side. I wish I had paid attention in speaker building class.

Now I'm left to muddle through. Dave, how would you modify this unit or is there something else that you have listened to? These units are selling for $269 on fleabay.

So I would put this before the amps in the signal path then bi or tri wire the speakers? We are getting to the point of having a lot of wires here. Not to say that I don't like wires and gagetry but I have to be convinced of a benefit.

I enjoy the conversations I have on here. This is probably one of the nicest forums I've had the pleasure of posting on.

Thank you.
-Spencer
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Old 21st December 2008, 04:35 PM   #7
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So, Dave, you are the exception that proves the rule

Empirically, it is a pro-sound piece, so it expects to see a signal that is hotter than what we are likely to feed it in home use. The less than full scale signal is then digitized using less than the 24 bits available. An unbalanced to balanced converter might help.

Another possibility to keep the DCX2496 running at higher levels would be to feed it an unattenuated (digital?) signal and attenuate the output for volume control. Of course a six channel balanced attenuator becomes expensive in a hurry.

Edit: The first link Pelle gave you has a diagram that shows how the connections are made right at the top of the article. Collectively the los pass and high pass filters are the active XO, which could be the Behringer.
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Old 21st December 2008, 04:40 PM   #8
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Quote:
Originally posted by EmergencyDpt
Now I'm left to muddle through. Dave, how would you modify this unit or is there something else that you have listened to? These units are selling for $269 on fleabay.
There is a whole industry modiying these units for home use. Expect to at least double the value of the unit.

Bob could have pointed out a valid reason why i found it poor.

dave
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Old 21st December 2008, 04:43 PM   #9
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This unit, being a pro-sound device is all xlr. That's not a road I'm ready to go down yet. Any other candidates anyone speaks highly of?
Thanks,
Spencer
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Old 21st December 2008, 04:45 PM   #10
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Double the value or double the price?
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