How do you cross over really low?

Nappylady · 25th June 2004, 04:06 PM

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?

markp · 25th June 2004, 04:12 PM

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.

Bill Fitzpatrick · 25th June 2004, 04:20 PM

A bandpass box is an option to consider.

sreten · 25th June 2004, 04:33 PM

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.

Bill Fitzpatrick · 25th June 2004, 05:07 PM

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?

sreten · 25th June 2004, 06:12 PM

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.

planet10 · 25th June 2004, 06:28 PM

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.

dave

BillFitzmaurice · 25th June 2004, 08:29 PM

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.

25th June 2004, 04:06 PM	#1
Nappylady diyAudio Member Join Date: Feb 2003 Location: Salt Lake City	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?

25th June 2004, 04:12 PM	#2
markp diyAudio Member Join Date: Oct 2003 Location: L.A., CA	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. __________________ If it sounds good... it is good!

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25th June 2004, 04:20 PM	#3
Bill Fitzpatrick diyAudio Member Join Date: Jun 2001 Location: Eugene, OR	A bandpass box is an option to consider.

25th June 2004, 04:33 PM	#4
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	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.

25th June 2004, 08:29 PM	#8
BillFitzmaurice Banned Join Date: May 2004 Location: New Hampshire	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.