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QSC PLX1602 and enclosures

Discussion in 'Amps and Cabs [BG]' started by dimi_did, Mar 17, 2005.


  1. dimi_did

    dimi_did

    Feb 17, 2005
    Montreal, Canada
    Hello,
    I want to buy a poweramp QSC PLX 1602 and one enclosure Aguilar GS212 under 4 Ohm.
    QSC sends 500 W under 4 Ohm or 1600 W in bridge mode and Aguilar accepts 600 Watts under 4 Ohm. Do you think that will function well together? Could you say me if I can use the bridge mode with this enclosure or they is dangerous? And can I use QSC PLX with only one enclosure without the bridge mode?
    Thank you in advance.
     
  2. msquared

    msquared

    Sep 19, 2004
    Kansas City
    You will be quite fine using a single channel of the QSC into that cabinet. The two would work well together. You could bridge it but I don't know that I would personally.
     
  3. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    HEADROOM!

    Judicious use of power is a wonderful thing.
     
  4. msquared

    msquared

    Sep 19, 2004
    Kansas City
    This is true. The cab would probably do fine if you bridged and just turned up halfway, which you might as well do if you're only running the one cab. The last time I had a PLX I did that and the difference wasn't all that noticable so I left it unbridged, but it wasn't running into a cab as nice as the Aguilar.
     
  5. dimi_did

    dimi_did

    Feb 17, 2005
    Montreal, Canada
    Thank you for your answer.
    And if I use an enclosure Aguilar GS212 of 4 Ohm and an enclosure of Aguilar GS210 of 4 Ohm - do you think that is well to function with this poweramp?
    Do you think that I will have good low registers with that?Because there are not many the enclosures of 1x15" of 4 Ohm. Generally it is under 8 Ohm. I don't know - why?
     
  6. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    With two 4ohm cabs, run the amp in Parallel mode with one cab off each channel.
    You can set each chnl's level independently.
     
  7. pickles

    pickles Supporting Member

    Mar 23, 2000
    Ventura, CA
    One side of a PLX1602 is more than enough power for my 4 ohm GS410, and I play loud. It never had a problem runnning just one side of the amp, and since there was an 18" sitting there in the practice space ... that other channel came in real handy :eek: Talk about a big sound!
     
  8. pickles

    pickles Supporting Member

    Mar 23, 2000
    Ventura, CA
    Most single driver cabs are 8 ohm, you are right, but don't let that stop you from using one! I think the 210 + 212 would probably have plenty of bottom end ... but consider that I run this 8 ohm 18 which is lower sensitivity than the 410 by a LOT in addition to being higher impedence. It really does fill out the bottom end. "On paper" it should not even be audible next to the 410, but it makes a huge difference in the overall sound.

    I run the attenuators on the power amp about the same (since its a friend's 18 and I don't want to blow it up), so it is seeing a lot less power than the 410, still it adds a lot of girth and boom to the sound, which I like.
     
  9. TheChariot

    TheChariot

    Jul 6, 2004
    Boston, MA
    Dont judge before you try. Give the 600Watts a try. 600Watts is PLENTY of power.... and if you end up pushing your headroom, than try it bridged.
     
  10. dimi_did

    dimi_did

    Feb 17, 2005
    Montreal, Canada
    Ok thank you very much the guys for this information!
     
  11. 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
    Turning the amp up halfway will do what for the cab?
     
  12. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    It would be reducing the total gain potential of the whole system, wouldn't it.
     
  13. msquared

    msquared

    Sep 19, 2004
    Kansas City
    Is that a rhetorical question?

    Because I'll answer it, but I get the impression that you're an engineer and already know what it'll do.
     
  14. 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, I know it won't necessarily do anything for the cabinet; it does not control how much power the amp can put out. Many users incorrectly infer that if an amp is rated for X watts and they turn it down a certain amount, the amp will only put out <X watts and is therefore safe for the speakers regardless of how they operate it. I wanted to make sure no one misunderstands what a gain setting is.
     
  15. msquared

    msquared

    Sep 19, 2004
    Kansas City
    That doesn't seem right. Let me blather for a minute and have you explain what I'm missing here.

    The way I understand it, signal path of a power amplifier such as the PLX 1602 includes an input stage and an amplification stage (and maybe others but those are the relevant ones). The input stage does any attenuation necessary and then passes the signal to the amp stage. The amp will apply an unadjustable ratio of amplification to that signal.

    If you have an amp that's rated to put out 1000 watts max into a given load, that assumes that the input gain isn't attenuated at all and the signal you're putting into the input stage of the amp is the maximum that the input stage is designed to handle prior to clipping. But if you were to, say, halve the amount of input gain, then the amp isn't going to put out 1000 watts anymore. The amplification stage is still capable of that amount and will put out exactly that much power (in theory of course) if it sees enough signal, but setting all knobs to 1 and playing with a gentle touch is not going to send 1000 watts into your cabinet.

    When you're talking about damaging a cabinet by excess power versus damaging a cabinet by sending a clipped signal to it, the idea is that you're safe as long as you're not pushing the drivers past their mechanical limit(s). So if I've got a 1000 watt amp and I've halved the input gain and I'm running into a cabinet rated as handling 500 watts (program/RMS/sustained/whatever), then why wouldn't a cabinet be safe from damage by the application of excess power?

    The clipping thing is another story of course.
     
  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
    You're assuming things that just aren't.

    If an amp is rated at 1000 watts into an 8-ohm load, for example, that means it'll put out a sine wave of at least 89.4 volts RMS (that can be calculated from SQRT[1000 watts * 8 ohms]) before it clips.

    If it has a maximum gain of, say, 60× (35.6 dB), that means that at full gain an input voltage of 1.49 volt RMS will drive the amp to its full, rated output. If you turn down the gain to, say, 30× (29.6 dB), then it will take an RMS input voltage of 2.98 volts to get the same on-the-verge-of-clipping output voltage of 89.4 volts.
     
  17. msquared

    msquared

    Sep 19, 2004
    Kansas City
    So you're saying that you can decrease the input gain and send a different signal level into the amp and still have the same non-attenuated signal level get to the amplification stage. I get that much.

    But ignoring the input gain, I'm assuming that the knobs on the front attenuate the voltage at some point before massive amplification happens. Even if that's not the case, when the knobs are turned to '5', it's not as loud as when they're turned to '10'.

    If I turn those knobs down, how am I still sending 1000 watts into a cabinet?
     
  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
    You don't have attenuated and non-attenuated signals. You're making distinctions that don't matter.

    If you put X volts into an amp with Y gain, your output voltage will be X*Y volts, as long as that result is below clipping. If you change Y, you can still get a certain value for X*Y simply by changing X.
     
  19. pickles

    pickles Supporting Member

    Mar 23, 2000
    Ventura, CA
    In other words, you set the gain on the power amp halfway up, thinking you can safely run your 500 watt cab with your 1000 watt amp, but then you can't hear yourself and you reach for the output gain knob on your preamp ... lo and behold you can drive that amp right up to 1000 watts output (and potentially blow up your cab).
     
  20. msquared

    msquared

    Sep 19, 2004
    Kansas City
    It's pretty apparent that there are three people who are not at all talking about the same thing here.

    I'm not confused about the hows and whys of clipped power hurting an amp cab. That is (more) important when you're talking about keeping cabs from an early death, but I've been assuming absolutely clean power for the sake of this discussion.

    I'm also not confused on how input gain works. Maybe I'm confused about how a PLX series amp works, but I don't have a schematic or block diagram in front of me so I've been making assumptions about what the front panel knobs actually do.

    This is what I'm curious about. The statement above seems to imply that an amp will still put out its maximum rated power if you turn it down halfway, and that seems totally incorrect to me. I'm assuming I'm misinterpreting something there, so could you please clarify?