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Am I underpowering my setup here? Please help

Discussion in 'Amps and Cabs [BG]' started by dusoe, Dec 10, 2006.

  1. dusoe


    Dec 10, 2006
    Hello everyone,
    I just recently bought a new cab. Gallien Kruger 1x15 GLX, and its rated at 200w. My friend is also letting me use one of his 4x10 cabs which is also rated at 200 watts. I currently have the Hartke3500 Transient Attack head, and I was wondering, by using both of these speakers, am I underpowering this rig? Would it be better to use only one 200watt speaker untill i can upgrade my head? Any help would be greatly appreciated.

  2. warswr


    Oct 21, 2006
    if you could tell us what the wattage on the amp is at 4 ohms (im assuming running those two cabs gives you a total 4 ohm impedance)
  3. Tom Ross

    Tom Ross

    Dec 9, 2006
    I all depends on your total impedence. If both cabinets are 8 ohm the you would be running the amp at 4 ohms and that is fine. Your will be getting the total of 200 watts that the amp is rated at and you will not be over loading the speakers, just be aware that the amp will distort not the speakers at full volume the 2 cabs can handle 400watts total together so you have to watch and not push the amp too hard as you don't have a lot of head room in a 200 watt amp, have fun and just save for a 400 watt or more head to give you more head room and a cleaner sound.
  4. dusoe


    Dec 10, 2006
    actually, to be totally honest with you, I really dont know. Would it be running under a 4 ohm load? Both the speaker outputs on the back of my head say 8ohms, Sorry im rather new at buying gear.

    Im looking everywhere online, and cant seem to find a damn thing about what the wattage would be under a 4ohm impedance.

    here is the GLX im talking about though...this seems like the best i could find.

  5. dusoe


    Dec 10, 2006
    yes, both cabs are 8ohms, so that means paired they would be running at a 4ohm impedance?
  6. dusoe


    Dec 10, 2006
    sorry about the constant posting, but im doing research as we speak. I just looked at my head online, and it says it powers at 350watts on a 4 ohm load, 250 watts @ 8ohms. The only thing that seems strange to me, is that the speaker outputs on the back say 8ohms, not 4. At any rate, since im running two 8ohm speakers, that means they are 4ohms correct? And so does that mean they are only getting 175watts per speaker?
  7. 12bass


    Jan 2, 2003
    Victoria, Canada
    Your Hartke 3500 head can power either two 8 ohm cabinets, or one 4 ohm cabinet. If both of your cabinets are 8 ohms, then you are fine (two 8 ohm cabinets in parallel give a 4 ohm load). Each 8 ohm cabinet gets 1/2 the power. Hartke probably marked the outputs with "8 ohms" so that you wouldn't try to plug in two 4 ohm cabinets because that amp isn't rated for 2 ohm loads.

    The problem with the concept of 'underpowering' is that it suggests that you are safer using fewer cabinets, or choosing cabinets with a lower power rating than your amp. That's just plain wrong.

    Here's more practical advice: If you are concerned about speaker safety, to prevent damage to the drivers watch the boost in the lows and back off on the gain if you hear distortion at high volumes.
  8. You cannot "underpower" a speaker cabinet and cause it to fail. If that was so, cabinets would be exploding everywhere due to being so severely underpowered as people abused them by turning them off. :D

    If the rig is loud enough for your needs with some room to spare, you will not have problems. If it is not, try turning down the low bass and boosting mids before you start hunting for a new rig.

    It's not "plain wrong" to use cabinets having an RMS power handling lower than the amplifier's RMS output. There are extensive discussions on this topic, but it is summarized by the FACT that most professionally designed PA systems utlize a roughly 2:1 ratio of amplifier RMS power to speaker RMS power handling. The reasons for this are manyfold any are already detailed in many other threads. Cabinets often limit the power handling of the system far more than the amplifier due to their x-max limitations, but the thermal failure of drivers is common and has a very clear cause.

    To answer your other questions, yes your two 8 ohm cabinets equal a 4 ohm load when they are connected in parallel (the only way you can connect them without modifying the cabinets or your cables). They will (roughly) divide power evenly between them so as your head can produce a maximum of 350 watts RMS, each cabinet will be required to dissipate a maximum of 175 watts each.

    Should your setup be insufficient for your volume needs, you will begin to clip (overdrive, distort, etc) your Hartke head's power amplifier section. The result of this is a very unpleasant tone combined with increased power output. In basic terms, a clipped waveform of the most extreme case begins to look similar to a square wave. A square wave has twice the heating ability (power) as a pure sine wave of the same peak-to-peak voltage. In other words, your amplifier will produce more than its rated RMS power when you distort it. Additionally, due to the compression caused by the distortion, your speaker cabinets will be dissipating this power on a more continuous basis rather than only on cleanly reproduced transients. THIS is what causes thermal failure of a speaker. It is still OVERPOWERING the speaker. Please keep in mind that in most cases, this needs to be an extremely overdriven amplifier well beyond the realm of what's "tolerable" to listen to. You'd know to turn down before this was likely to occur.

    Hopefully this helps out a bit.
  9. 12bass


    Jan 2, 2003
    Victoria, Canada
    Perhaps the context of my comment was misunderstood.

    What I was suggesting was that some people claim that, rather than 'underpowering' a cabinet with a power rating greater than a given amp's output power, the solution is that one should replace that "over-rated" and "mismatched" cabinet with another cabinet with a lower power rating, say 1/2 the amp's output power.

    However, given that many ported bass cabinets are already xmax excursion limited to 1/4 of their rated power at low frequencies, this would further decrease the power handling of the cabinet to a maximum of only 1/8 of the amp's output power at low frequencies, which a dangerous move in the wrong direction. Thus moving to a cabinet with a lower power rating is clearly not a reasonable solution as it only exacerbates the potential risks for driver damage from overexcursion.

    Clipping the amp and headroom are a whole other discussion....

    Read Bill Fitzmaurice's comments here:

  10. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Quite right. The entire notion of matching cabinet and amplifier wattage ratings is flawed. The wattage rating of the cabinet only says how much power it was designed to accept without being damaged. How much power is required to drive it to its full undistorted output capability is a different question entirely. 10% to 50% of rated power is the range.
  11. dusoe


    Dec 10, 2006
    wow, thanks everyone, never really expected such great replies. You've definitely eased my paranoia a bit. The volume im getting out of my speakers seems to be just fine for what I need them to do. I suppose the best bet in the near future would be to purchase a new head, then upgrade the cabs. Again, thanks so much for all of your help!
  12. Very good points. Pardon me for taking it in the wrong context, but you're absolutely right.

    Great post.
  13. chad.planet


    Jan 10, 2011
    Best answer I found on the thread, he's right.
  14. Zombie Thread..............

    Besides, we ALL KNOW that underpowering is a myth anyway - right ?

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