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Final word - Amp wattage vs. speaker rating

Discussion in 'Amps and Cabs [BG]' started by Chad Michael, Nov 6, 2002.


  1. FretNoMore

    FretNoMore * Cooking with GAS *

    Jan 25, 2002
    The frozen north
    [​IMG] Very useful info, thanks!

    Seems to give the same answer as the rule-of-thumbs of 1.5-2 times the power rating of a speaker that has been mentioned here a couple of times.
     
  2. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Hmm ... I dunno if I'd call that the last word. Seems to me it's more like a case of someone who's kinda right, but for some kinda wrong reasons. There are several things in there that just don't make much sense IMHO. But he's quite right that it often works great to use amps rated for more than the speaker's rating.
     
  3. What this doesn't mention is the fact that you can use an amplifier with less than optimum power and run your speakers (subs, P.A., bass guitar cabs, etc)

    All day long

    Provided that you

    Don't drive the amp hard enough to clip!!!

    Of course, you will never realize or utilize the potential of your speaker system this way.

    (Just my 2 cents and it's probably worth less than that if you disagree....)

    B
     
  4. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    For the first part, absolutely!! You're exactly right.

    As for the potential thing, I dunno. If a speaker does what I want it to, then it's realized its potential as far as I'm concerned. Doesn't matter that I never drive it to its limits.
     
  5. Maybe not exactly the last word, but it's actually pretty reasonable. A bit simplified, but that's a good thing for non tech junkies.... There are a couple of puzzle pieces missing. Overall there's some good information on there.
     

  6. There are situations where you could drive an amp into severe clipping and not worry about blowing speakers too! We'll just say that clipping doesn't necessarily destroy speakers....;)
     
  7. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Quite so. If it did, all the speakers in probably every Marshall guitar stack on earth would blow right away, all the time. Which they don't.
     
  8. Agreed... I believe that the reason they don't blow is because the amplified signal, going to the speakers, is:

    1) Inherently very compressed (due to the way the signal is processed in the preamp and poweramp section)

    2) Lacking the sheer amplitude that is present in the signal going to a P.A. cabinet, subwoofer, or bass guitar cabinet

    Just my theory..... yours?

    B
     
  9. Sheer amplitude has it. Too much power burns out voice coils in cone speakers. Basically, if the continuous average amplifier power exceeds the continuous average power rating of the speaker you will eventually damage the voice coil. This is irrespective of the waveform. So clipping doesn't necessarily burn out voice coils. You could severly clip a 100W (continuous average) amp into a speaker rated for 500W (C.A) all day and not be real concerned about cooking thevoice coil. At the absolute maximum, that amp could produce 200W, which the voice coil could easily dissipate. The story is a little different for HF drivers due to the harmonic makeup of amplifier clipping.
     
  10. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Well, as for 1, I think that, if true, would make damage more likely rather than less--higher average signal level.

    And as for 2, I don't think sheer amplitude, in an absolute sense, matters, because what damages drivers is not "too much" power in any abstract sense, but *too much power for that particular component*. A 30 W guitar amp can more easily blow a 15 W Vox Blue Bulldog speaker than a 300 W bass amp can a 1000 W EAW subwoofer.

    I think the reason that the Marshall speakers don't blow constantly is simply that even with all the distortion (and clipping) in a typical rock guitar sound, the amp doesn't develop a high enough average signal level to exceed the speakers' power handling capacity. In other words, clipping in itself isn't a problem; the problem with clipping is when it results in some component somehow getting more power than it can handle. But enormous amounts of "clean" signal can do this too.
     
  11. Right. The compression issue didn't occur to me until after I posted. But you're right, because compression increases the average amplitude of a signal.
     
  12. My SWR Triad is rated at 400 watts RMS. That means I need to devide it by 2 or 200 watts and then multiply it by 4 so I should 800 watts RMS right. Now SWR says:
    "Power Handling:
    The power output rating for any amplifier connected to Triad should not exceed the enclosure’s 400 watt RMS power handling capacity. Please be aware that exceeding Triad’s power handling capacity can void the SWR warranty if any damage occurs to your loudspeakers due to overpowering." This is quoted directly from the manual.
    What do you suppose SWR would say to me if I fryed my speaker with a 1000 watts (which I use) and I said "According to a post on Talk Bass I'm suppose to use at least twice the RMS rating of the speaker in order to get a 6db headroom over the AES rating"????:confused:
     
  13. Yep.

    I've got a novel idea...
    Have the amp match the cab.
     
  14. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    See, that exemplifies the whole problem I have with links like the original one (and I'm not trying to bag on bimp, who was endeavoring to help).

    They make the assumption that headroom has something to do with your cab's power handling. It really doesn't. What determines your headroom is how much of your amp's available power you're using (how much you have to turn up to get the volume you need). If your 400 W amp is easily enough to get you the volume you want (without straining or clipping) with any cab of a given efficiency X, then using a cab rated to handle 200 W rather than 400 does absolutely *nothing* to increase your headroom. (If anything, it could slightly reduce it, if your speakers start complaining at an earlier point on the power output curve.) In that setting, you can use a 400 W cab, an 800 W, and often a 200 W, and it's OK.

    But if your 400 W amp is not enough for the job, and you have to push it too hard--again, a 200 W cab won't protect you from clipping. More likely, it will mean earlier onset of speaker damage.

    It's still true that you can very often use, say, a 1000 W amp with a 500 W cab--people do it all the time. It works because they typically don't use most of that 1000 W in the course of playing, or only in short bursts. But this kind of amp-cab ratio doesn't help headroom, and it's not inherently better than using a matching cab or a higher-rated cab. In this scenario, any headroom advantage you gain is the result simply of having an amp bigger than you need, not of having a lower-rated speaker. You'd get the same advantage with a 1000 W cab of equal efficiency.

    My rule of thumb is, get enough amp to get your max needed volume with ease, or even a little more amp than that, and then get *at least* enough speaker to handle the highest level of power you're likely to use, or more speaker than that if you have the bucks and want a little extra protection.
     
  15. Don't worry about disagreeing with me or bagging on me, I actually enjoy hearing your point of view.

    *I've seen so many threads on this subject
    *I've heard so many bass rigs / P.A.'s / subs that sound like a toolbox falling down a flight of stairs
    *Too many times I've listened to people who hadn't a clue about power
    *Too many times I am asked "Why does your P.A. / bass rig sound sooooo much better than ours?"

    I thought the link might provide some insight to those who ask, and those who have systems that clip and sound like shiite.

    Sincerely,

    Chimp-gimplet
     
  16. Here's another link regarding the subject matter:

    http://www.jblpro.com/pages/general_faq.htm

    Personally I regard JBL as a great product (with a few notable exceptions) and, considering their extensive background with pro sound and cinema applications, probably right on the money with their information.

    Enjoy.

    B
     
  17. I've heard this method for matching power amps to speakers before. In fact it came from an EV technition when we were trying to match our speakers to the Crown K-2 amps we were using. We ended up under the recommendation of Crown and EV bridging the k-2 into a pr of EV subs. That's 1200 watts per sub each sub has 1x18 rated at 400 watts rms. And we did the same thing with the tops. They used the same method described in the link. The message I get from all of this is "To get the best sound, DO THIS but if you BLOW SOMETHING well TOO BAD". I've powered my Triad with a 400 watt amp and I've powered it with 1000 watts. Believe me it sounds better with 1000 watts, and I don't play it all that loud.
     
  18. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Check out this one.

    http://www.rane.com/pdf/note128.pdf

    Also, check out this doc from the JBL site, and pay particular attention to the right hand column on p 3, where it talks about different types of applications, including musical instruments, PAs, and studio monitors:

    http://www.jblpro.com/pub/technote/spkpwfaq.pdf
     
  19. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    I believe you, definitely. My only point is that it would sound just as good with a 1000 W cab of equal tone and sensitivity, because you would still have the same volume and headroom. And you would be less likely to blow something because your speaker could handle more power.