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Discussion in 'Amps and Cabs [BG]' started by screamingdaisy, Sep 25, 2005.

  1. I'm currently using a guitar cab, and the sound is starting to grow on me.

    What I'd like to do is build a crossover to protect the speakers from the lower frequencies. The cab's loaded with Celestion Vintage 30s

    Spec Sheet

    So....how would I go about building one? Or am I best off getting the guy at the stereo shop to build me one?
  2. You're a bass player, not a guitar player. The goal is to PROJECT the lower frequencies, not PROTECT the cab from them.

  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You don't want a crossover, you want a high-pass filter, and that you have to do electronically.
  4. The 0x

    The 0x

    Aug 24, 2003
    Timonium, MD
    Just don't go too heavily on the bass knob, and you'll be fine. Eventually, you'll want a 1x18 or something to go under that. But I must admit, 4x12s do sound nice for the mids & treble on a bass guitar. :bassist:
  5. Tash


    Feb 13, 2005
    Bel Air Maryland
    You'd probably be better off using a biamp rig and sending your lows to a real bass speaker than removing them from the mix entirely. Lows are our job.
  6. I tried biamping with a guitar 4x12 for the upper frequencies. I also figured that if I kept the volume knob reasonable I'd be OK.

    Wrong. Evidently 250 watts into a guitar cab rated 100 watts was a little too much. Overheated a couple of voice coils....
  7. I'll be running two cabs.....one of which will be a bass cab.

    Thanks. I'll do some research into them.

    That's the plan. Two different preamps into each half of a power amp.....one high-passed, one full range.

    My guitar cab's rated at 380w.....so I should be alright.
  8. Quadzilla

    Quadzilla Supporting Member

    You are eventually going to blow those speakers. Get a bass cab...
  9. So now I'm confused...

    you like the sound of the guitar cab, which are typically low on bottom end. And want to add a "bass" cab to get the low end back.

    But instead of a biamp rig, where the bass just adds the bottom lacking from the guitar cab, you want to run it full range, where its midrange can color/mess with the midrange of the guitar cab you like so much.

    And typically the low end needs the help, not the mids, mids are relatively easy to produce. So the bass cab full range with the 2nd cab doing mids is kind of backwards. Usually you want to add more speakers/cone area to help out moving air to get enough bass volume to match the mid volume which is easier to achieve.

    The two preamp thing could be problematic too, looks good on paper, more control, etc. But if you have too much mids or highs, which speaker is the culprit? Which preamp do you adjust? I think in practice 1 preamp is better.

    I'm just not sure your game plan is totally sound, its kind of let's say "unorthodox".

    But if it sounds the way you like it when you're done, that's all that matters.

    So Bill is right, you need high pass filter (usually low level, so it would fit between preamp and power amp, or in the effects loop, not something you'd install in speakers like a "crossover").

    If the guitar cab is open back, there's no damping, you DO have to eliminate the lows from it. It has guitar speakers, so they're not high excursion to begin with, and without a sealed or ported box, there's no air damping the speakers to help prevent overexcursion. Also the back wave tends to cancel out the front wave, requiring even more excursion to produce any low notes. They'd be very prone to bottoming out, so you DEFINITELY need a relatively high freq high pass filter to prevent that.

    I think you're more in danger of overexcursion damage than overpowering the cab, like you said its pretty high wattage for a guitar cab. The high pass will be critical...

    My 2c on the dual preamp, don't. See what the cabs sound like together (don't forget the high pass filter!) if the "bass" cab mungs up the midrange of the guitar cab in full range mode, run it in biamp mode for just the bass. You like the sound of the guitar cab for your mids. Let it do the mids without interference.

    Doesn't hurt to try stuff, even though you're going at this a little differently than the conventional wisdom. Good luck, let us know how it turns out.


  10. Thanks. That helped alot. The whole idea is still in the experimental stage. What spawned the whole thing is that I recently plugged into an Ampeg SVT-3PRO and Ampeg PR-410HLF.....I loved the bottom end, but I couldn't dial in a midrange I was happy with. Maybe I just need more time on that amp/cab setup, or possibly hook that amp upto another cab (I did like the bottom), I'll give it another shot before I go spending $$$ on this idea.

    Originally I planned on running the "bass" amp fullrange....but I'm taking what you said into serious consideration. I'm not really into all bottom bass tones....but I see where too much midrange could be problematic too.

    The guitar cab in question is a Mesa Rectifier 4x12.....oversized & sealed enlosure. It's designed for de-tuned guitars, but my bass is throwing alot at it. I've talked to one other forumite who's using a similar setup (Tosya) and she says she's been using it fullrange without any filtering....but I'd like to stay on the safe side and add some anyway.

    Thanks again for the open minded opinions.