Dismiss Notice

Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

one more QSC question for the day

Discussion in 'Amps and Cabs [BG]' started by Ego, Sep 19, 2005.


  1. Ego

    Ego

    Jan 10, 2004
    i'll be playing a QSC PLX 1602 into a Mesa/Boogie 18''. the cab is 8 ohms, and says 'power capacity 400 watts' (i'm guessing that's RMS rating). so, if i run through a single channel, i get 300 watts, which is pretty much groovy. however, if i run in bridged, i get 1100 watts. now, i did do a search, and i think i learned a little, but i can't afford to replace this equipment if i screw it up so i want to be totally confident in what i'm doing. would it be dangerous to run in bridged mode if i'm careful of the volume? i know headroom is good, generally speaking, and i know the amp can handle more than mono mode can give, so... how can i get the best sound and not break my equipment?
     
  2. xb100

    xb100

    Mar 24, 2004
    NH, In
    You CAN bridge your mesa into the qsc, but be VERY CAREFUL and watch your volume. Make sure you have a speakon cable also.

    -Rob
     
  3. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    No, it will not be dangerous at all if you are careful of the volume. Just listen as you play. As soon as the speaker starts to fart or show any other indications of straining turn down until it goes away and then leave it there.

    As a bass player you will NEVER produce a continuous sine wave by playing music (unless you are feeding back). RMS is an average. The PEAK wattage is the true indicator of what your speaker can handle at extreme volumes but only for a very short time. As long as you AVERAGE 400w rms you will be fine.

    IF...and I say IF your speaker does blow and you are being careful as described, it will not be from the power feeding it but from a wear/quality/engineering issue. Which can theoretically happen at any time anyways.

    Disclaimer: **** happens.

    :D

    Joe.
     
  4. Ego

    Ego

    Jan 10, 2004
    cool. thanks for the info :)
     
  5. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    If you're the paranoid type, you can use the PLX's clip limiter and the 30Hz filters. Those won't guarantee you won't screw something up if you don't listen to your cab, just makes it a little more difficult to screw it up.

    Sometimes watching the cone movement will give an idea of how hard the driver is working (although some drivers are designed to move more than others.

    Also, be careful when using bass boost as this can seriously jack up the power pulses sent to your driver.
     
  6. 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
    You can bridge the amp, but not a loudspeaker. ;)

    If you avoid clipping the amp or having it put out high power at excessively low frequencies (that's what the filter is for), the loudspeaker should be fine. Keep attuned to your sound, and as Joe said, if you hear farting or bottoming out, back off on your levels right away. That doesn't mean you have to be on edge all the time, though. Use that ample power for headroom.

    In my own rig, for over seven years I've been quite successfully running a PLX 1602 in bridged mono (1000 watts into 8 ohms) into an 8-ohm EX cabinet rated at 200 watts continuous power. Except for at turn-on, I've only seen the clip LEDs light up a couple timnes. I wouldn't recommend this 5:1 ratio for everyone, but it's not necessarily disastrous when in careful hands.
     
  7. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    I always know if my GK/JBL rig is being pushed too hard because the ports start "chuffing". (I - uh.. assume that's what it is!). It's quite noticeable - and by that time, if you look at the speaker excursion, OY!

    Joe
     
  8. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    Yeah, if the cone(s) looks like it's trying to jump out of the basket, you'd better back off quick.
     
  9. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    I was going to post this in another thread, but that thread got closed down.

    I did some experimenting with my PLX1602 and I found that I definitely don't like what the 30Hz filter does to my sound.

    Now this is possibly just a result of the particular bass, preamp, and cab I'm using (along with my tone settings), but it seems very strange to me that it would have any sonic impact at all (other than tightening up the very low end -- which in fact it did do).

    I guess it is also possible that the observed effect was totally in my head, but I did try it twice over two days -- switching it back and forth.

    I'm not sure how to describe the resulting sound except to say that it sounded very unnatural in the mid-bass and lower midrange, instead of its usual organic type tubey tone.

    I did try tweaking the tone settings on my Demeter to try to dial out some of the weirdness, but without any real luck.
    I did get it sounding just a little better, but nothing like what I'm use to with my usual settings.

    [Just for reference the usual settings on my PLX are all the DIP switches to the left except the bridge switch which is to the right (no I don't use the clip limiter either).]

    Anyone else out there have anything remotely like this happen to them?
     
  10. 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
    You should use the clip limiter as a safety net. There is no advantage to leaving it off unless you need distortion when the amp clips.
     
  11. E.O.M.

    E.O.M.

    Dec 7, 2001
    Grand Rapids, MI
    From what I've read here, I would say that it is much safer to run that setup bridged than in a single channel. By running 300 watts into a cab rated at 400 watts, you run the risk of clipping the amp -- and almost doubling the power produced. It would be much less likely to clip the 1100 watts in bridged mode. Then, the only thing you have to worry about is what has been mentioned before -- putting too much power into the cab, which is easier to control than clipping an amp to get more volume.
     
  12. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    Thanks.
     
  13. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    I do run it bridged.
     
  14. E.O.M.

    E.O.M.

    Dec 7, 2001
    Grand Rapids, MI
    Good. I wasn't correcting you, I was answering your question. :bassist:

    We all hate blown speakers. :bawl:
     
  15. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    Cool. I wasn't sure.

    My cabinet is so efficient and projects so well that in bridge mode the amp is just loafing along, maybe hitting the -10dB lights on peaks.
    I've never seen the clip lights flash while I'm playing.

    The only time it ever shutdown on me was a thermal thing at a 4th of July outdoor gig (Texas -- no PA bass support).
    I put a stand fan behind the rig and no more issues.
     
  16. 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
    The likelihood of clipping the amp is not related to the loudspeaker's power rating, but the potential risk to the loudspeaker is.

    A general rule of thumb is to use amp power that is up to about double the loudspeaker's continuous powe rating. Then the amp's clip indicators would also serve as warning that you could be overpowering the loudspeaker as well.

    Ego: If your cab's continuous power rating is 400 watts, you'd look for an amp rated at about 800 watts into 8 ohms. Your PLX 1602 is rated at 1000 watts in bridged mono into 8 ohms. That's a reasonably good match.
     
  17. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    The cab is rated at 1400WRms; it's 4ohm, so the PLX is rated at 1600W with that load.

    I guess I'm a bit underpowered, the 2x point would be 2800W.
     
  18. 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
    Yes, underpowered in theory, but perhaps not in reality. The bottom line is that if you can get the sound levels you need without the amp clipping, you have enough power.
     
  19. MODNY

    MODNY Guest

    Nov 9, 2004
    so...

    if i bridge my crest ca9 at 4 ohms (2000 watts) into my accugroove 2 10 and 18 (combined rms @ 1400 watts) it should be fine eh? and sound pretty sweet?? i've been wondering about this aswell

    thanks
     
  20. 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
    If their impedance is 8 ohms each, yes, that'll work.

    Be aware, though, that two dissimilar cabinets connected together in parallel might not sound alike, and the balance between them might not be to your liking.