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Wattage question

Discussion in 'Amps and Cabs [BG]' started by BassMisfit, May 15, 2001.

  1. BassMisfit


    Dec 31, 2000
    Irwin, PA
    This may be a dumb question, but does the speaker or the amp make the wattage? Because I see speakers in Carvin's mag for 300 watts and I was wondering if I put that in my amp if I could turn up more w/o getting the overdriven buzz noise I get now? This might also be due to the fact that my speaker was blown before I got the amp and then repaired! Anybody know how to fix this w/o buying a new amp?
  2. the amp makes the wattage, the speakers carry that out.

    when a carvin speaker says "300w" it probably means that's what it can handle from an amp.

    ie: if you run a 1,000w head amp through that 300w speaker, the speaker will smoke.
  3. There are many after-market speakers. Find out if your amp should have a 4 ohm or 8 omh speaker, then shop for speakers which will take a little more power. JBL makes solid bass speakers and they are easy to find.
  4. rllefebv


    Oct 17, 2000
    Newberg, Oregon
    True, however, it is fairly easy to blow a speaker with too little wattage. That same 300W speaker can blow if you're cranking a 100W head into clipping distortion, (Square waves = no bueno for speakers). Believe me... I've twice blown 400W cabinets with a 150W head trying to play at gig volume before I was hipped to this fact... (Yes, the ohms matched up...)

    IMO, it is preferable to run a higher wattage head into a lower cabinet. Granted, care needs to be taken... But the extra headroom is easier to deal with. I've run my Carvin RC210 bridged at 600W into the 400W cabinet for two years with absolutely no problems. If I was still trying to reach those same volume levels with a 150W head... Uh uh!

  5. MikeyD


    Sep 9, 2000
    I think it is doubtful that one can damage a cabinet rated for 400 watts RMS continuous with an amp rated for 150 watts RMS continuous, no matter how hard it is overdriven. Such an amp will be capable of 300 watts total square wave output, so a 400 watt cabinet can handle it, if the ratings are honest. However, if the cabinet has a tweeter, the tweeter might be damaged by the high frequency content of the clipped waveforms - especially if it has no "tweeter protection" device. For example, I have an old 2x15 cabinet (~ 200 watts handling) that could easily take full clipped output from the head (<100 watts RMS) probably for weeks without even sneezing.

    Another thing is, square waves are quite normal for instruments that are deliberately overdriven (e.g., via distortion pedals) or for some synthesizer waveforms. Obviously, speakers can and do handle them just fine if rated to take the associated power.
    - Mike
  6. I have been wondering about this too, Mike. I've heard a few more stories like this, and I don't think they're all lying. Would the high frequency content of the clipped amp have anything to do with it? I.e. if you drive a woofer with very high frequency glitches, like from a clipping amp output, would this somehow change the way the coil behaves and heat it up more? A disto pedal will be HF filtered by the preamp. A preamp clipping will be HF filtered by the various filter sections in the output drive stage. An power ouput has no filters, except maybe an oscillation protection, which isn't really a filter, rather a damper.

    Dunno, really.
  7. MikeyD


    Sep 9, 2000
    Hi, Joris! We're playing "message tag" today! :) Anyway, you make a really good comment, and I appreciate how you presented it. I agree that extraneous high frequency output generally gets transformed into heat in the coil, since the typical woofer cannot respond adequately to the associated MMF (magnetomotive force). I have worked with motors that simply swallowed extraneous HF output from chopper and SCR motor drive circuits - the effect was not to produce additional usable torque, but to add to the heating load of the motor (and make whining noises from the windings).

    I think that normally an amp's square wave (fully clipped) output power is about twice its sine wave RMS output. This is the basis for my previous post. However, you allude to something altogether more serious: amplifier instability. I've seen cases (in poorly designed or improperly biased amps) where the amp could go into serious high frequency oscillation (e.g., at 100 kHz) and there's no knowing about it for most of us except to notice the heat and smoke! That energy could be damaging to the power stages and the speakers, for sure. But again, given what (little) I know about amp topology, the power supply rails limit the maximum voltage of even the unstable oscillation's output. So one might argue again for the "power doubling" scenario. My reaction to an amp that did such a thing upon onset of clipping is that is a poorly designed one. Well-designed amps should not be putting out damaging waveforms or DC on their own.

    A long time ago you and I had a debate about the possibility of DC being generated by an amplifier driven into clipping. It is an interesting point. I remain skeptical right now, but if you ever measure such a phenomenon or locate a tech. paper on it, do let me know. I'm open to the possibility...

    - Mike
  8. You guys might want to check out:


    Select PDFs | Articles & Whitepapers

    Get the "Anatomy of an Amplifier" PDF. This is *very* informative about amp classes, DC generation, etc.
  9. MikeyD


    Sep 9, 2000
    Thanks for the reference, bgavin. QSC does have a lot of informative material on their web site. I learned a lot about power consumption by reading PDFs of their power amp specs. The article you mentioned is definitely a nice overview. The phenomena that Joris and I are discussing gets a bit esoteric, and I'm at risk of getting in over my head because I'm not an amp designer (i.e., I know enough about EE to get myself in trouble! Actually I know a bit more about it than that... :) ). But even this QSC article talks about anomalous behavior that shouldn't happen, such as "snapback" and oscillation. I didn't see anything regarding an amp putting DC into the speaker outputs, though.
    - Mike

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