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question on clipping! *confusion*

Discussion in 'Amps and Cabs [BG]' started by Yossarian, Jul 15, 2004.


  1. Yossarian

    Yossarian

    Jun 24, 2004
    Virginia
    Okay I've been reading a bunch of the old threads on this forum about amplifier clipping. My amp is 475 watts RMS and my cab is 350 watts RMS and 700 watts program. The impression I got was that 700 watts program means 1400 watts peak, and that the most power my amp is going to put out in extreme situations... like clipping i guess... is twice the RMS rating... 950 watts. and if the cab is 1400 watts peak, that's not going to hurt it if it's only for a little bit... right?

    I have this feeling I have got this all entirely wrong. Please correct me if I do.
     
  2. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    You have it entirely wrong :rolleyes:

    Your amp is 475 watts RMS, then clipping will occur when output exceeds 475 watts.

    Your speaker is 350 watts RMS, program rating is double that (700) so you are all set...your amp when driven to the point of clipping will still be less than the program handling rating of your speaker.
     
  3. Yossarian

    Yossarian

    Jun 24, 2004
    Virginia
    okay, that makes sense... but how does the output get to exceed 475 watts? how does that happen?
     
  4. Yossarian

    Yossarian

    Jun 24, 2004
    Virginia
    I mean... I'm reading that thing Joris wrote about clipping, and it leads me to the same question. "When a power amplifier is forced past its maximum output power, it will clip." How do you force an amplifier past its maximum output power?
     
  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
    No, this is not correct (except maybe that you ruined a reverb unit).
     
  6. cgworkman

    cgworkman

    May 14, 2004
    Ohio
    Yes you're correct. I am wrong. I was reading through some postings here on TB referring to some similar questions. In my mind I had 2 or 3 different answers merged into one. After searching and finding that thread - I saw my mistake :crying:

    Your turn...
     
  7. 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
    Every amplifier has a maximum output signal voltage that it can produce into a given load. If you put too hot a signal into the amp, crank its gain too high, or both, you will make its output hit those limits.

    Here are some simplified charts showing a signal from an amp. The white horizontal lines depict the maximum positive and negative output voltage the amp can produce. Depending on the amp's output power rating, these voltages could be ±25 volts, ±60, ±100 volts, or whatever. The higher the amp's output power rating, the higher the voltage at which it clips.

    The first chart has the peaks hitting at about half the maximum output voltage, or about 25% of full power.

    The second one has the peaks hitting at or near full power.

    Go on to the next message …
     
  8. cgworkman

    cgworkman

    May 14, 2004
    Ohio


    Mr. Spock? ;)
     
  9. 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
    The third one has the peaks trying to go well beyond what the amp can produce, and so the signal gets chopped off, or clipped.
     
  10. ESP Eden

    ESP Eden

    Feb 9, 2004
    washington mo
    Clipping is just how it sounds. It clips your signal peak, like a distortion pedal would, only it is in your power amp. Sort of like a compressor. It does that so that the amp can put out more power. But this is bad for the amp, and your speaker if it cant handle the power.

    Someone correct me if I'm wrong.

    EDIT: what bob said.
     
  11. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA

    Hmmm.... It would be nice if things were that simple. But they're not. There is no "fixed" relationship between RMS power, program power, and peak power. There are "general guidelines", but each manufacturer has a slightly different way of measuring things, so one has to take the ratings with a grain of salt.

    In general, here's how I interpret things. The "peak output voltage capability" of the amplifier (that Bob Lee referred to, which relates mainly to the power supply voltages, assuming it's a solid state amp without an output transformer) determines the point of clipping. The clipping behavior isn't really related to the RMS rating at all.

    The "RMS" rating has more to do with the ability of the components (transistors, transformers, etc) to deliver "sustained" energy, which relates mainly to heat dissipation, and the internal construction of the components (semiconductor junction properties, that kind of thing). You can have an amp with a 100 watt RMS rating, that's capable of delivering over a thousand watts of peak power. That happens "all the time" in the world of car stereos, for example. Check out some of the ratings on the car subwoofers, for instance, and you'll see what I mean.

    The "program power" is more like an "average" value that's supposed to take into account the fluctuations around the mean. That's very important in the world of bass playing, because a good bass will have a very wide dynamic range, and the signal peaks are typically 5 to 10 times the average power level. That's why bass players who use solid state amps typically need "a lot" of power. For instance, my Walter Woods Ultra will easily deliver 1200 watts of peak power into a 4 ohm load, but when it's run at that power level, the "average" power is probably around 300 watts. To my ear, it's just about as loud as an SVT through a fridge, when it's cranked all the way up.

    Because different amps are built differently, you'd have to know a whole lot about the circuit, and the components, in order to make a knowledgeable prediction about the relationships between the different types of power. A tube amp, for instance, will generally be incapable of delivering peak power that is significantly in excess of its RMS rating. That's just the nature of the beast, and it's because of the way the tube circuits are designed, and the way the tubes themselves operate.

    On the other hand, if you have a solid state amp that uses transistors rated at a thousand volts and 100 watts, and your supply voltage is only 200 volts, there will be plenty of headroom and you might be quite surprised at the level of peak power the amp will deliver, "until" the transistors get hot enough to go belly up. At that point, you will have exceeded the amp's RMS capability for a sustained period of time.

    It all gets very wierd when one starts talking about the different types of circuits (eg complementary versus cascade), and the different types of transistors (eg MOSFET versus power Darlington), etc. I wouldn't put too much faith in any "simple" relationship between the different types of power. My best suggestion is, to listen to your amp and your speakers. If things sound like they're getting wierd, it's time to shut down for a while.
     
  12. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    What nonsqtr said is essentially true, but it can be simplified a lot.

    First, the RMS (!) power corresponds to a peak power double that. So a 100W amplifier putting out 100W already has 200W peaks.

    Also, generally, with SS amplifiers, the maximum instantaneous peak power (measured with one pulse) is only about 1 1/2 times the peaks that occur at max RMS power. It is a rare amplifier with a "dynamic headroom" higher than 2 or at most 3 dB.

    So you can usually count on no more than 3 or 4 times rated power as the worst peak that could occur. And even that will be a peak that lasts only a tiny time. It won't bother most speakers.

    Tube amps may do a bit more, but even they have limits, and can only provide the biggest peaks for tiny times.

    Then, speakers can generally take much more power in a single pulse than they can continuously. Tweeters obviously have lower limits than heavy-duty bass speakers, but both can take transient peaks.

    If the cone doesn't get pushed into the magnet, a transient peak of 10 times power rating is not unreasonable for a speaker to take. That would be at higher frequencies. At lower frequencies cone travel may force a lower power limit.

    I would not obsess about it unless your style and playing is really loud and / or clipped.

    Most makers will rate a 100W RMS speaker for 200W to 300W "program", and 300 to 500W "peak". And that is perfectly OK.

    If your style is industrial grunge metal, or you crank the lows way up, you might want to be more conservative on ratings. Speaker RMS rating closer to amp power.

    And if you are gonna clip a lot, that raises the average power, and you again would want to get closer to the RMS rating of the amp with your speakers.

    Don't sweat it too much, get out and play. Most of the time, if there is a problem, it will be frequency-related, not just power related. And you will probably get quite a bit of warning when it sounds kinda nasty due to major clipping, speaker overtravel, speakers farting out bigtime, etc. So turn down and bring more speakers next time.