help with my QSC Ashdown rig

Discussion in 'Amps and Cabs [BG]' started by bassguppy, May 24, 2005.

  1. Hopefully someone with any technical expertise can chime in here.

    My Gear:

    QSC RMX1450
    Ashdown ABM210
    Ashdown ABM115
    Sansamp RBI
    5 string bass

    Both cabs are 8ohms. QSC bridged into 4ohms for 1400 watts. QSC filter at 50hz.

    my question: is there a way when bridging that you can limit the lower frequencies into the 210 cab. Such as say a capacitor to cut below 40-60 hertz while still bridging the amp in order to get the max power. Then switch the low freq QSC filter to 30hz. Mainly I want to run the 115 full range but cut the lowest frequencies to the 210.

    Could I possibly use a mono 2 way crossover?

    Also, how would I wire this setup?

    Any knowledge vaster than mine is greatly appreciated.
  2. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    --Can you limit the lows going to the 210 with a crossover? Yes.
    --Can you do that while bridging the output from the QSC into both cabs? No.

    If you're bridging the QSC, you have one single output that goes to both cabs in series, adn that output is going to be the same for both cabs. Crossovers run before the power amp section, so that you get different inputs to each of the amp channels, but that only works if you're running the power amp in stereo so that you actually have two separate channels to work with.


    PS: You might simply try lowering the filter on the QSC to 30Hz and see what you think of the results.
  3. Yeah I have biamped before & I know this is not a biamping situation. Just trying to be cheap by not getting another amp.

    I wasn't sure if there was something you could use when daisy chaining the cabs.

    from the QSC bridged w/30hz filter----to the ABM115----to some sort of filter or capacitor cutting below say 50-60hz----to the ABM210.

    seems plausible but only on paper.
  4. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    Yeah, I had some idea what you were hoping for. I'm just pretty sure that none of those capacitors/filters are intended to handle the current of a power amp output.

    What benefit, precisely, are you hoping to get by not sending those 30-50Hz frequencies to the 210? That might make a difference in assessing possible solutions.

  5. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    You could try running the amp in parallel mode, with the filters set suitably. You'll lose about 4dB of headroom but you're running fairly efficient cabs which will probably over-excurse if hit by 1400W of bass, and 600W or so should get them pretty damn loud.

  6. Mainly want to use it as a safety factor. Not to waste amp power on a cab that doesn't produce the lowest freq's clearly.

    Each cab is rated at 300 watts RMS. with the QSC bridged each cab would get about <700 or so watts. I have been bridging the amp with the amp set around 2 o'clock & preamp about 1 o'clock. It's giving me that bit of extra volume I need but not quite doing it for me sound wise (a little middy) or too much out of the 210. Before I ran the amp parallel with the 115 around 4 o'clock & the 210 around 12 o'clock & had a decent tone happening but not the volume.

    For tone I prefer more lows. maybe I just need a bigger amp so I can run 2 channels. :(
  7. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    I'm not sure how that's a "safety factor", really. However, if you're trying to avoid wasting power on the power amp side by sending "unused" frequencies to the 210, you'll have to filter them out *before* they get out of the power amp. Otherwise, the power amp is still sending them (and using up current in the process), even if the 210 isn't trying to reproduce them.

    Yeah, I'm afraid a bigger power amp is going to turn out to be a much better solution, even if you run both cabs in full-range mode (except for the low filter setting). Plus, that gives you the ability to set the blend between the two cabs.

  8. oh well, back to the bread lines. :smug:
  9. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    bassguppy, if you have the filter engaged and set to 50 Hz, you're already rolling off the frequencies that you're talking about rolling off. If you want to filter the two cabs differently, then you should put them on separate amp channels, as Alexclaber (getting to be quite the tech support anorak, Alex! ;) ) and others have suggested.

  10. yeah, I figured I'd have to have separate channels. Just wishful think and me being cheap I guess. I'm already pricing an RMX2450. I'm just cheap, but overall I think I will be more satisfied.

  11. andruca


    Mar 31, 2004
    Madrid (Spain)
    You can calculate the capacitor for a 1st. order filter just to do a test (cheap!). As you use both cabinets un parallel, only half the power will go to the 2x10" cab (700W). The maximum voltage your amp can produce bridged is:


    Any capacitor beyond 79V should work ok. Now I don't know how to calculate the capacitance but I got some tables that read 200uF for a 100Hz hi-pass filter (in an 8ohm speaker). So maybe you can try 100, 150, 200, 300 and 400 uF to find out which you like best (the higher the value, the lower the cut will be). As it is rare to find non-electrolitic capacitors within this uF range, you can simply "de-polarize" using two capacitors the following way:


    (-) wires joined and (+) wires on both ends.

    This way, you put up a non-polar capacitor which's capacity is:

    (CAP1*CAP2)/(CAP1+CAP2) or CAP1/2 if both capacitors are the same value.

    I think you can find such a thing at any electronic components store.

    This is only a 1st order (3db/octave) hi-pass filter and I'm not sure if that's enough to do a good test (amps' filters are mostly 4th order -12dB/octave-) so maybe you'll only notice on the higher frecuency cut ranges (lower capacitance). Anyway I think it's cheap enough to give it a try, mostly in order to clarify if you like what you hear with the 2x10" cab filtered.

  12. tbitsky


    Apr 15, 2005
    Um, I know this really doesn't answer your question, you really NEED to be louder?

    I mean, it sounds like you have a very nice setup there, and the RMX1450 should be plenty loud for any small to medium gig. 1400 watts isn't efficient enough?

    If you're experiencing GAS and want to improve your rig, why not upgrade your preamp? If it has a line level control, you might be able to get more volume out of your power amp by sending a stronger line signal.

  13. There is no need to be louder. the 1400 watts is more than fine. but i was leery of running both cabs full range so I wanted to cut a bit of the lows to the 210. the RMX1450 in stereo will only give me 300 watts a side at 8ohms. Also, I want more control over the cabs volume wise where I would rather get more out of my 115 rather than the 210 which in combination sounds a little middy.

    So the reason I'm considering the RMX2450 or some other higher power amp is because both my cabs are 8ohms, so I will not be getting the max potential out of the amp but I will get 500 watts per side out of the QSC which should be sufficient and give me more control (I HOPE). :)
  14. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    But have you tried it like this, to find out how loud 'only' 300W per cab actually is? If it's not enough to drown out many drummers, I'd be surprised.

  15. I would have to agree with BassGuppy's plan to go with more power per channel and run his rig in parallel mode. :)
    For what I'm doing, my RMX1450 is plenty. I run an 8ohm 210 and a 4ohm 410. The 50 Hz filter is on on the 210's channel, the 30Hz filter on the 410. Having them run this way also allows for the 6db difference in sensitivity and more control of the lows.
    I do think we should always support a compatriots quest for more power though.... ;) Go for it!
  16. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    Since I'm running with an RMX2450 myself, I obviously support that plan!

  17. the only thing I'm not thrilled with the QSC RMX series is fan noise. Obviously you can't here it when playing but when quiet I can here that sucker 10 feet away.

    other than that great amp & great bang for the buck.
  18. LiquidMidnight


    Dec 25, 2000
    Oh yeah, the fans are pretty loud. The only thing I don't like about the RMX's is the weight.

    The production company that ran sound for us two weeks ago was using about 6 RMX's (along with some PLX's). Needless to say, the racks they were in were situated on dollies. *LOL*