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UNDERpowering speaker cabs

Discussion in 'Amps and Cabs [BG]' started by dancehallclasher, Oct 22, 2001.


  1. ok, take a bag end S15-D, handles 200W continuous. say i hook it up to my SWR workingman 15 combo, thereby running 100W into it. is this really bad, and if so, only bad at high volumes or what?

    i'm wondering because i've heard of those little smokey amps powering 4x12 guitar cabs, in fact they recommend it on the website. so what's the skinny?
     
  2. Oysterman

    Oysterman

    Mar 30, 2000
    Sweden
    Underpowering a cab is in itself not dangerous. The danger with not having enough power/headroom is that if you turn up the amp until it starts clipping, which will cause damage to the speaker (at least with SS amps). If you have lots of power available you'd be able to get the desired volume without stressing the amp.

    And my favourite band rocks. ;)
     
  3. 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
    Underpowering a speaker is dangerous only

    A. if you run the amp into heavy clipping, and

    B. if the amp is powerful enough to damage the speaker when it clips.

    An amp's power rating is measured with sine waves and with little or practically no distortion. But with severe clipping, the waveform shape will approach that of a square wave, which has a lot more power and a lot more distortion.

    For example, an amp rated at 200 watts with a sine wave could put out up to 400 watts with a square wave, at least for a short time. And if the signal is high enough to cause clipping that severely, even when it drops below clipping it'll be at a very high level. Therefore, the average power will be extremely high, and at times possibly higher than the amp's 200-watt rating.

    Therefore, if the amp is driving a speaker rated at, say, 250 watts or so, there's a strong chance that it could burn out.

    But if you're badly overdriving a 50-watt amp into a 500-watt speaker, you're not likely to damage the speaker even though you're underpowering it and also driving the amp into severe clipping. But it'll sound like crap.
     
  4. so basically, if i keep the gain at a reasonable level and avoid clipping, i should be ok?
     
  5. 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 you do that and can get the sound level you want, you're good to go.
     
  6. 72beetle

    72beetle

    Jun 10, 2001
    Phoenix, Arizona
    VERY nice! Hey, check out the <a href="http://www.minibosses.com">Minibosses</a>, they do great video game soundtracks too!

    -72
     
  7. Oysterman

    Oysterman

    Mar 30, 2000
    Sweden
    Thanks man! I've been wondering for a long time if there was someone who shared my perversion for old video game music! I will definitely check them out! :D
     
  8. lol Oyster!

    I was just playing that game (Castlevania IV) the other day and thought about how cool the basslines are in some of those songs...

    Excellent job on the bass, man!

    Didn't mean to hijack the thread there.

    Also, I don't think I can add much to what Bob said, since he pretty well knows all when it comes to amps and things. :)
     
  9. wouldn't another speaker give me more volume anyway?

    i'm kinda confused here... does adding another speaker have any effect on whether the amp clips or not? because currently i'm not using any extension speaker, and i don't drive my amp into clipping, so would adding another speaker change that?
     
  10. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    Minibosses rock!! I saw them when they were still up here in MA. Good show!!!
     
  11. Oysterman

    Oysterman

    Mar 30, 2000
    Sweden
    Yes, and add to that it would allow you to run your amp at the full power rating.
    It will change to the better - since you will have more power available from your amp (running in 4 ohms as opposed to 8 without ext. speaker) and increased speaker area will "fill the room" more than the single speaker on your combo.
     
  12. Oysterman

    Oysterman

    Mar 30, 2000
    Sweden
    Try playing some of the lines in that and other games - many of them are have quite unorthodox rhythms and patterns... loads of fun! :)

    I think I will put some more work in that MP3, though - the playing is a bit sloppy, the strings were rather dead (never heard such a dull slap sound before ;)) and I feel a need to develop the MIDI instrumentation, especially the drum track (I borrowed the whole MIDI backdrop from www.vgmusic.com and only added bass, some EQ and reverb).

    This is definitely the wrong thread for this, though. ;)
     
  13. 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
    It might. A lower load impedance will draw more current from the amp at any given output voltage, and that heavier load will make the amp clip at a somewhat lower output voltage.

    For example, let's say your amp clips at 40 volts RMS into an 8-ohm load. (That's 200 watts.) You add another 8-ohm cabinet, so now it's got a 4-ohm load. If it's got a good, strong power supply, maybe it'll clip at 36 volts now (324 watts). If it's got a soft, wimpy power supply, maybe the clipping point will sag down to 32 volts (256 watts) or lower.

    But for any point below clipping, you'll still have twice as much power as before (a 3-dB increase), and if your cabinets are close together and facing in the same direction, you can get as much as another 3 dB of acoustic coupling (meaning the acoustic power from the two cabinets will reinforce straight out to the front, but may cancel to the sides or at other angles).
     
  14. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    Hi Bob could you take a look at my thread about power amps and maybe give me some advice? It's the power amp, how would you do this? thread. Does QSC make something along those lines? Thanks -Josh
     
  15. ok, thanks everybody. so i guess the final verdict is, i will be good to go as long as i don't crank it and try to cause earthquakes, right? cool.

    see, i don't have enough dough to buy a good full rig at once, so my long-term plan is

    1) get the bag-end cab, use it as an extension.
    2) sell my combo and buy a carvin power amp for the 15", with my sansamp as a preamp.
    3) get another 15" or a 4x10 or both, eventually, as the poweramp does 350 watts/side at 4 ohms.
     
  16. CrawlingEye

    CrawlingEye Member

    Mar 20, 2001
    Easton, Pennsylvania

    That's the cool thing about combo amps that can hold extension speakers.
    I used to have a Peavey 210TX.
    I bought my Peavey 410TXF to add to it, later got my Firebass head, then just last year got my 115BXBW. :)
     
  17. Robert B

    Robert B Supporting Member

    Jan 21, 2000
    Hampton, Va USA
    Hey DHC -- Who in the area sells Bagend?
     
  18. www.skmac.com seems to be the dealer in this state. i was planning on just ordering one anyway.
     
  19. 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
    Hi Josh, I looked at your thread, but I'm not clear on what you want to know.