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Crossover/Low Pass filter for 2x10 cab?

Discussion in 'Amps and Cabs [BG]' started by PolkaHero, Jul 1, 2005.


  1. PolkaHero

    PolkaHero Supporting Member

    Jan 5, 2002
    Michigan
    I'm looking for a crossover or low pass filter unit that will attenuate the low frequencies from reaching my Avatar B210 cabinet. I'm running it with either 2 Bag End S15Ds or 2 SWR Big Ben cabinets with a QSC PLX3002 power amp and the 50Hz filter on the QSC just doesn't do an adequate job of keeping the Avatar from bottoming out on the lower notes. Is there a rackmount crossover unit that I could set up to keep the lows (say under 100 Hz) from going to the 2x10 yet have the Bag Ends or SWRs still running full range? Thanks!
     
  2. PolkaHero

    PolkaHero Supporting Member

    Jan 5, 2002
    Michigan
    I've looked at these crossovers already, but I'm concerned about the power handling capability. These are rated at 250 watts RMS, while I am running at 450 watts RMS. I'm using this setup at outdoors festivals, so I'm cranking it pretty good. Is there a rackmount unit that would work as well? Thanks for you replies!
     
  3. No, not that I've ever found. You'll probably need to go with an active crossover and biamp your rig. I'd recommend a 2nd order crossover. I've tried 4th order crossovers and wasn't happy with the results. The 24db per octave slope on 4th order crossovers is too steep and the top cab and bottom cab sound "disconnected" from each other. I'm much more satisfied with the results from a 2nd order crossover. Problem is, the availability of 2nd order crossovers is getting kind of limited. Most of the majors have dropped them in favor of 4th order which sound guys prefer for PA systems.
     
  4. SteveC

    SteveC Supporting Member

    Nov 12, 2004
    North Dakota
    I think you'll need to bi-amp to do what you are trying to do. Try a Rane DC24. It's a dual band compressor, but has a built in crossover as well. Not only can you set your crossover point, but you could run different effects and compression to differentn cabs as well. Just a thought.
     
  5. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Those pre-fab autosound crossovers won't do it. Bi-amping is one alternative, but since you're never going to be able to use a Delta loaded 2x10 with any authority at 50 Hz anyway I would put a high-pass filter inside the box. You don't need anything fancy, a first order filter at 120 Hz would keep out the low stuff they can't handle without potential phase issues. You need to know the cab impedance to figure out the capacitor value. As far as a rackmount passive crossover goes I doubt if there's any such thing, and having a cap inside the cab is a lot more convenient.
     
  6. PolkaHero

    PolkaHero Supporting Member

    Jan 5, 2002
    Michigan
    How hard is it to wire those crossovers from Parts Express? Anybody here do this in a smaller cabinet? One more gig, I'm going to fry at least one Eminence Delta speaker. . .
     
  7. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Wiring them is easy, but they aren't what you want. If you install a 2nd order (or higher) HP filter you must always have another speaker to handle the LF load. Use the 210 without another speaker for the low end and the filter could put a destructive load on your amp. You want a 1st order high pass (a capacitor) only so you can use the 210 with or without another cab. The PE HP filters are also designed for 8 ohm loads. if yours is a 4ohm cab it won't work.
     
  8. Steve

    Steve

    Aug 10, 2001
    Parts Exp. also has a LINE LEVEL filter called an FMOD. They come in all kinds of frequency ranges.

    If you happen to be running stereo..you could put one between the preamp and the power amp channel input that runs the 210 cab.....

    They work, They're cheap. I have one in the effects loop of just about everything I own for...just in case situations and bad rooms.

    http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=266-274
     
  9. PolkaHero

    PolkaHero Supporting Member

    Jan 5, 2002
    Michigan
    Bill,

    Do you have a link to one of these? My cabinet is rated at 8 ohms, BTW.
     
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Those FMods would be cool if they came in 1/4" jacks. They're not as usefull in the current RCA format.

    Polka, something like THESE should do it.

    For an 8 Ohm cab, you'll need a capacitor with a value of 200uF for 100Hz. All you have to do is place the capacitor inside the cab somewhere in line with the positive speaker wire.

    Because they're not expensive, it's no big deal to experiment with capacitor values, so I'd buy several and swap them out until I'm happy. For reference, 250uF = 80Hz, and 160uF = 125Hz. So the smaller the capacitor value, the higher the crossover point.
     
  11. I don't know how you're feeding the different cabs with the QSC but if you had one channel dedicated to the B210, you could very simply and cheaply put a 0.22 uF polyester cap (Such as http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=020-1840) in series at the input of the power amp channel driving the B210. This would give you a 1st order high-pass filter @ about 120 Hz. If you want to experiment with different cap values / frequencies, the formula is:

    Cutoff freq = 1000 / (2 * PI * Zin * C),

    where Zin is in kohm (6 kohm for the unbalanced input of the QSC PLX amp) and C is in uF.
     
  12. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    That's Cool!

    What's the formulas for 2nd order?
     
  13. If you go here http://www.passivecrossovers.com/index.htm and click on "Drawing the numbers" you will get the formulas for Butterworth 1st to 4th order passive filters. "The circuitry patterns" gives you the schematic for each type. That page refers to speaker crossovers but the formulas are valid for any passive filter (where it says "speaker impedance" use the input impedance of the amplifier).

    The problem is that, as you can see, from 2nd order upwards you need to use inductors, and if you do the numbers you will get insanely high values. Even the inductors used in loudspeakers, which are three or four orders of magnitude smaller than what you would need here, are bulky and expensive. That's why, other than the simple single capacitor / 1st order I suggested, active filters are always used at line level. Btw if you're good with a soldering iron these are also very easy to design and build. Analog Devices has a very nice online tool that gives you the schematic and component values for most filter types and orders from 2nd to 8th: http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/filter/filter.html
     
  14. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Thanks for those links. I've already got that passive crossover link
    (which BTW is an excellent resource) and am fairly well versed in that area.

    When you started talking about putting a filter at the input (pre amplification) stage, I realised I know nothing about active filters. So I'll go and teach myself something new. Thanks.
     
  15. I use the Fmod on my amp for a subsonic filter. 20Hz. You can get 1/4 to RCA adapters. It would work fine if you pick the right freq for the cutoff.

    I don't like having to use the cheesy 1/4" to RCA adapters, though, but its lesser of 2 evils, better than wasting power, excursion on subsonics.

    Randy
     
  16. Steve

    Steve

    Aug 10, 2001
    it WOULD be nice if they came in 1/4 jack config...especially since it probably is just a case for a little filter cap...

    It's still a great thing to stick in an effects loop to kill mud.

    They can have a profound effect on an Acme cabinet.
     
  17. PolkaHero

    PolkaHero Supporting Member

    Jan 5, 2002
    Michigan
    Pete,

    Just ordered three of these capacitors from PE. Thanks alot for your input. I decided this is probably the easiest and cheapest way to solve this problem. Just hope it can handle the power I'm sending to the cab. BTW, how did you come up with those frequency values?
     
  18. DaveMcLain

    DaveMcLain

    Jun 19, 2005
    Cuba MO
    This evening I was tinkering around with my bass rig which consists of a SansAmp RBI, Crown Macro Tech 1200 and Euphonic NL-210 cabinet. This thing sounds great but it seemed to me that if you put much emphasis on the low end at high volume that it was a little too much way down at the bottom. When I would thump the strings it would hit the speakers pretty hard. I solved the problem by using some info from the Crown Website and the manual for the amp. I use the XLR input and I just added a .1Mf capacitor to each leg of the input, this was easy to do on the removable PIP module but it wouldn't be a hard mod on just about any amp. At first I put two caps in series on each leg for .05Mf and that was a little too much rolloff. Going to one of the .1Mf caps per leg is just right, it didn't change the sound much except in the very low register, it's really tight and controlable now, punchy, sounds excellent...