Passive Crossover / In-Line Filter ?s

ncbassman · #1 04-08-2010, 01:56 PM

I have a single 18" in a cab (I know not optimal, could of used a 15 to be more efficient). The cab was given to me and it just has a straight from speaker to input dish. It was an old Carvin V118 (from the early 90's). I called Carvin, and they confirmed that the dish was just a straight input, with no crossover or filter. I plan on using a 2x10 or 4x10 cabinet with a tweeter on top of this cabinet.

I would like to keep high frequencies out of the 18" cabinet. About 400-500 Watts will be going to it. It is an 8-ohm speaker. I have done some reading and assume I need a passive low-pass crossover, and that an in-line filter will not work for the amount of wattage I want to run it at.

I was looking at this crossover:
http://www.realproaudio.com/eminence...ver-p-279.html

Does anyone have any good references for installation of passive crossovers? I tried to search and couldn't find any (just conversation about which X-over is correct, etc...). If I Google it all I get is car audio resources.

Any help is much appreciated, If I used a wrong term, take it easy on me, I'm still a newbie in this area.

4Mal · #2 04-08-2010, 02:10 PM

Review the fEarful wiki on crossovers. Lot's of good info up there. If it were me, I would think about mounting the x-over to the shelf port in the cab. That way the 2x10 or 4x10 can act as a full range cab with no other junk in the way... Unless you are really way too loud, a 2x10 ought to do fine particularly if you care keeping the sub 100 hz signal out of it...

Use some kind of standoff to keep the x-over off the shelf itself. If the cab is particle board then I might mount the x-over to a piece of play using wood screws run through short lengths of surgical tubing as the standoff. Glue the plywood to the shelf. If it's plywood, just screw into that...

Add a 'unique' jack to the input plate to serve as the 'hi' out to the other cab. By unique I mean different from the existing one to prevent you from mis-wiring the cab's. I used 1/4" in from my amp and 4 pole speakon out. My x-over is implemented in an external box.That way I can bi-amp or run passive depending on which rig I'm carrying...

BassmanPaul · #3 04-08-2010, 02:15 PM

By far the better way of doing this is to use a separate amplifier for the lows and use an active crossover.

Paul

ncbassman · #4 04-08-2010, 02:15 PM

Thanks for the quick reply. The cabinet is birch. As a end result, I would like to use this cab with a 2x10 cab (two 8 ohm cabs) to get a 4 ohm load to maximize my amp. I'm not as concerned about keeping the low freqs out of the 2x10 as I am protecting and keeping the high freqs out of the 1x18.

Do you have any pics of your external box crossover? It seems like that would allow for more flexibility if I decide on different cabs down the road.

billfitzmaurice · #5 04-08-2010, 04:18 PM

Quote:

Originally Posted by ncbassman

I'm not as concerned about keeping the low freqs out of the 2x10 as I am protecting and keeping the high freqs out of the 1x18.

If you use a passive crossover with two 8 ohm cabs you will still have an 8 ohm load. In any event the difference in response between an eighteen and a pair of tens is far less than you might think, so you'll get little benefit from a second order or higher crossover. You'll get the best result with a simple first order network with a 200Hz corner frequency, and that means build your own. How is explained here:
http://www.bcae1.com/xoorder.htm

4Mal · #6 04-08-2010, 04:29 PM

Quote:

Originally Posted by ncbassman

Thanks for the quick reply. The cabinet is birch. As a end result, I would like to use this cab with a 2x10 cab (two 8 ohm cabs) to get a 4 ohm load to maximize my amp. I'm not as concerned about keeping the low freqs out of the 2x10 as I am protecting and keeping the high freqs out of the 1x18.

Do you have any pics of your external box crossover? It seems like that would allow for more flexibility if I decide on different cabs down the road.

Yep - the amp will only see 8 ohms after the crossover. The box is exactly that. A Greenboy Cheap But Good 12/6 for Alpha with an additional 6 bd pad to cut down the mid/hi's a bit. In a wooden box with a 1/4" and a speakon. Not much to look at there ... but there are pic's in the Wiki...

I'm thinking that you aren't really providing any protection for the 18... more like the 2x10 ... I ran an SWR 18 under an SWR 2x10 powered by an SVT III as a rehearsal rig for awhile. Both cab's went full range. Sounds pretty darned good to me ... the SVT III ran out of gas for that band's gig volume but it was a loud band...