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Old 17th January 2005, 10:48 AM   #1
keyser is offline keyser  Netherlands
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Default bi-amping (active crossover)

hi guys!

i plan to bi-amp a pair of 3-way speakers. 1 amp for the 2 woofers, and 1 for midrange and tweeter. To do this properly i have to use an active crossover. would a standard PA-crossover work, or do I need a crossover specifically made to fit my speakers?

thanks!
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Old 17th January 2005, 11:53 AM   #2
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A PA crossover may work, but it will be far from optimal.
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Old 17th January 2005, 12:43 PM   #3
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why would it not be good?
i've seen some with very precise frequencie settings, and 1st order filters. In what way would it be different from a custom made filter?
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Old 17th January 2005, 02:45 PM   #4
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A PA crossover may work, but it will be far from optimal.
Just prejudice or based on what?

If a very flexible unit is wanted - try the behringer dcx 2498 - search in this forum for evaluation. I have one that replaced a marchand kit xover of very good quality (not only my opinion) that i had for 8 years in different configurations - and find no sound degradation.
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Old 17th January 2005, 04:14 PM   #5
keyser is offline keyser  Netherlands
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my speaker is a 3 way design, that crosses over @ 300 hz, and 3500 hz. I need a 2-way crossover: i'll leave the passive crossover at 3500hz in place, just to be sure not to blow the tweeter when switching on the poweramp.
I'm not sure, but i think the passive crossover in my speaker is a 3rd-order filter. Most active crossovers are 1st-order, though.
would an active 1st-order filter not be better than a 3rd-order?
Isn't the main reason speakermanufacturers use 3rd- or even 4th-order filters, that those are cheaper?
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Old 17th January 2005, 04:41 PM   #6
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My statement was based on the fact that a some -- particularly budget -- active crossovers have only a few frequencies to choose from. If you can choose the frequency to within 10% of ideal and the slope is also correct, then by all means go ahead with a PA crossover.
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Old 17th January 2005, 05:19 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
I have found that most commercial active xovers ar either 2pole or 4 pole, with either Butterworth or Linkwitz Reilly cutoff. I bought a subtractive LR many years ago and hated it. Some time later I was able to measure the cutoff slopes and much was revealed!
The behringer can do all of these and a few (lot) more.
Big down side with behringer is the almost fixed output level after the filters. You need to add some kind of analogue attenuation before the power amps.
BTW most speaker manufacturers avoid 4 pole passive xovers because of the excessive cost. The cheap ones use just mechanical rolloff and single pole. Ugh.
regards Andrew T.
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Old 17th January 2005, 05:32 PM   #8
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You can attenuate input and output levels - only to within =/- 15 db's
and it is rather cumbersome. But - if you run your source signal to a preamp, and then to the dcx - you do not need that.
The problem might be that you then work in the digital domain with a non optimal input signal level.
Don't know if that could cause signal degradation.

I just run two six gang potis (available through "thel" in germany at a decent price, but they do not ship overseas - needs agerman adress) between the dcx out and the amps.
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Old 17th January 2005, 11:01 PM   #9
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Quote:
Originally posted by keyser
my speaker is a 3 way design, that crosses over @ 300 hz, and 3500 hz. I need a 2-way crossover: i'll leave the passive crossover at 3500hz in place, just to be sure not to blow the tweeter when switching on the poweramp.
You will now need the woofer and midrange leads from the X-over attached to the midrange unless you are keeping the Xover point the same. The passive is needed to protect the tweeter full time not just at start-up.
Quote:
[i]I'm not sure, but i think the passive crossover in my speaker is a 3rd-order filter. Most active crossovers are 1st-order, though. [/B]
Incorrect
Quote:
[i]would an active 1st-order filter not be better than a 3rd-order? [/B]
That depends but not usually
Quote:
[i]Isn't the main reason speakermanufacturers use 3rd- or even 4th-order filters, that those are cheaper? [/B]
No, quite the opposite. 1st order is a 6dB per octave, 2nd is 12, 3rd is 18 etc. The steeper the slope, the more parts are required.

Why not snap a pic of your Xover and post it for us?

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Old 17th January 2005, 11:38 PM   #10
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WHOOPS, i was mistaking about the order of filters and their steepness. thought about it the other way around (first order being a 24db filter)
posting a pic of the crossover is a good idea. i'll do that soon.
my speakers are Canton RC-L. throught google you'll find a lot (atleast i do here in the netherlands)

It is my intention to set the active X-over @ 300 hertz (same frequencie as it is now). send the signals to 2 different poweramps.
connect the outputs of the <\= 300hz (bass) amp directly to the terminals of the twin woofers.
connect the output of the >\= 300hz (mid\high) amp to the mid\high terminals on my bi-wirable speakers.

is this the right way? I said previously that most active x-overs are 1st order, but i meant 4th-order ofcourse.
so: would an active 4th-order filter not be best?
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