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Old 25th June 2004, 04:06 PM   #1
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Default How do you cross over really low?

My PA system is currently active, crossed over at 200hz from the woofers to the wide-range cabinets... I've been wanting to convert to passive, in order to make setup simpler and get my feet wet with passive crossovers... but when I start looking at the lowpass filter for the woofers, it seems that to maintain my 200hz crossover, I need a 25 mH inductor, and I suspect that if such a thing existed, it would weigh half as much as the rest of the woofer!

I know there's got to be a simple way to cross over at 200hz passively without having such huge component values, but I don't know what it is.... can someone help me out here?
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Old 25th June 2004, 04:12 PM   #2
markp is offline markp  United States
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Low freq=big coil. Thats why most use active crossovers for subs(in addition to power wasted). Large coils like that are best on transformer cores to make them more efficient(smaller). Speaker City sells such coils as do others.
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Old 25th June 2004, 04:20 PM   #3
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A bandpass box is an option to consider.
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Old 25th June 2004, 04:33 PM   #4
sreten is offline sreten  United Kingdom
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I don't know where you've got 25mH from for 200Hz.

Extremely unlikely to be correct.

Active c/o at 200Hz is so superior you shouldn't consider passive.

Note that two 100w amplifiers actively crossed over at 200Hz
is equivalent to one 400w amplifier with a passive crossover.

sreten.
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Old 25th June 2004, 05:07 PM   #5
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Quote:
Originally posted by sreten
I don't know where you've got 25mH from for 200Hz.

Extremely unlikely to be correct.

16 ohm driver maybe?
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Old 25th June 2004, 06:12 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Bill Fitzpatrick


16 ohm driver maybe?
Well I checked that, and it is right for 2nd order L/R 16 ohm 200Hz,
you'd also need the same inductor value for the midrange unit also.

Just think 16 ohm is a poor load for PA use, and unlikely.

sreten.
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Old 25th June 2004, 06:28 PM   #7
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Quote:
Originally posted by sreten
Active c/o at 200Hz is so superior you shouldn't consider passive.
What he said... you could perhaps build the amps into the box to simplifiy set-up.

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Old 25th June 2004, 08:29 PM   #8
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There is no reason why going passive would simplify your setup, asuming that you have your amps and crossover are rack mounted and pre-wired so that all you have to do is plug in the master AC, the board and the speakers. If you're wiring everything up from scratch at every gig that's the first thing you want to fix.

Going passive at low frequencies is expensive, wastes amp power, and results in poorer sound quality overall. As someone else noted if you go passive you'll have to go with one much larger amp instead of two smaller ones. You can't even buy high end PA speakers that use passive crossovers. There's a reason. No pros would want them.

The one mod you should make is to wire the outputs of your amps to 4 pole Speakon outlets mounted on the rack case, and make up a four conductor cable going to a four pole Speakon jack on the woofer boxes. Also install a second set of Speakons on the woofer, parallel wired, and use those to send the mid/HF signal out on a 'shorty' cable that plugs into the mid/HF boxes. That way you only need a single set of long cables to get the signal out to the stacks.
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