Distortion: Bad for speakers?

Discussion in 'Amps and Cabs [BG]' started by PanteraFan, Oct 15, 2001.

  1. Hi. I was just reading through a Trace Elliot technical manual(as you do...hey, it's a Monday night!)and I saw that they say square edge distortion kills speakers very easily. This I already knew(and understood). What I don't get is that you see people who use distortion/overdrive pedals or effects into their speakers, and you hear nothing about damaged speakers. Are these effect units somehow special, do they produce a non-square edge signal?
  2. downstairs


    May 13, 2001
    Pasadena, MD
    distortion pedals create an acceptable amount of distortion, and its quite different from square edge distortion ( to my knowledge ).
  3. well perhaps it kills T.E. speakers :p
    But my Eden can handle any signal, as long as it's < 500w i'm sure :)
  4. Yeah, Celestions are really sucky speakers...:rolleyes:

  5. Luis Fabara

    Luis Fabara

    Aug 13, 2000
    Ecuador (South America)
    Audio Pro - Ecuador
    The distortion they mean is totally different from what is generated by a Tube Preamp or a distortion pedal.

    What they mean is Squarewaves that are produced because the power amp cant put any more clean power.
    These squarewaves will make the cones move back and forth heavily to the extremes causing extreme coil heat and posibly break it.
  6. MikeyD


    Sep 9, 2000
    Synthesizers can produce very good square waves, and if this is all that was needed to destroy speakers, no one would ever dare generate an audible square wave. I have detailed explanations of this whole subject in past posts. It's primarily the power produced by a clipping amplifier that can damage speakers - if the resultant total power is in excess of the handling capability of the speaker(s). There is also some consideration of the high frequency energy contained in a square wave that can sometimes destroy tweeters for the same reason.
    - Mike
  7. Mike, I'm not sure how relevant this is. In the manual, it specifically says that the TE speakers could handle at least 100W more than thew speakers were rated at, as long as it was clean signal and not distortion. The only thing that would kill them is the distortion...?

  8. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    There's no one answer because the question is too vague.

    No speaker can reproduce a true square wave because to do so would require the cone to move instantaneously. The problem with square waves is when you start approaching the excursion limits of the speaker, now you are asking the speaker to move from all the way out to all the way in in ZERO TIME. Push it just a bit harder and you're asking the voice coil to jump the gap (fatal).

    So square waves at power levels close to the rating of the driver are indeed dangerous.

    Since tweeters in most bass and PA cabinets handle much less power than larger drivers, they are usually the first to blow from square waves.
  9. MikeyD


    Sep 9, 2000
    I don't see why this would be true. Power handling is power handling. If the full power of the square wave (including harmonics) is accounted for, and it doesn't exceed the handling capability of the driver, then there should not be a problem.

    PanteraFan, most of the confusion arises from the difference between RMS continuous sine power (the usual amp rating) and the power yielded from the amp when clipping or driven with distorted (e.g., square) waveforms. Comparing the RMS sine rating of the cabinet to that of the speaker is a good way to ensure compatibility. But if you have distorted output, the actual output power will exceed the RMS continuous sine rating of the amp. For example, a 100-watt "RMS" amp can put out nearly 200 watts of square wave power.

    As I said before, this subject has been covered in depth in TalkBass.

    - Mike
  10. jasonbraatz


    Oct 18, 2000
    Oakland, CA

    yup. and that's what caused my 15" speaker in my SWR triad to die. i drove it and an goliath jr with a bass 350 and it was almost always driving to the limits.

  11. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    Power handling is based on many things: cone excursion, ability to dissipate heat, etc.

    A speaker is a mechanical system. A square wave properly reproduced would move the cone from one extreme to the other in zero time. This of course can't happen, it does take time to move in and out. But what happens when you get all the way to the end of cone excursion? There are no disc brakes on the cone, it has to be slowed down, stopped and reversed by reversal of current in the voice coil. Imagine expecting your car to go from 60 mph forward to 60 mph reverse in zero time. The less quickly the cone can respond to the change of current, the more likely it is to move farther than it is supposed to...possibly jumping the gap.

    So the only question is how much power ABOVE the speaker's nominal rating will cause overexcursion and how well damped is the speaker and amplifier system.

    To put it another way, if someone had a cabinet rated for 200 watts, drove it with a 200 watt RMS head and played nothing but fuzz bass through it at maximum volume, I would NOT be surprised if they blew speakers on a regular basis.

    Read speaker specs published by EV and others where they discuss how to interpret power handling specs. The primary concern is distortion in the system. A speaker does not know or care if the distortion is due to amp clipping or a fuzz box.
  12. jasonbraatz


    Oct 18, 2000
    Oakland, CA
    and that's why they make guitar speakers with a LOT less cone movement and much stiffer than bass speakers, right?

  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
    However, speaker continuous power ratings are primarily based on thermal conditions, not overexcursion. At a constant acoustic output, a speaker cone's excursion is inversely proportional to frequency. Therefore, if power ratings considered excursion, they would have to specify frequencies also.

    As Mike said, this topic has been discussed a lot here at TB. It's not the shape of the waveform that kills speakers; it's excessive power.

    For a really good explanation of clipping an dits risk to speakers, see http://www.rane.com/pdf/note128.pdf.
  14. Mike, Bob, and others, I'd like to comment on all the good comments made here.

    How about a heated voice coil that's driven with a lot of high frequency due to a clipping amp? Would the attachment of the voice coil to the cone suffer more than with low frequencies? If the cone is forced to make these very fast movements, I imagine the forces on the coil and the coil-to-cone attachment are immensely high. Maybe it'll rupture before you reached the maximum thermal power of the coil. If the coil is already hot, it'll maybe even speed up the process.

    Just a thought.

  15. MikeyD


    Sep 9, 2000
    Hi, Joris - you have a valid point. In my view, the wattage rating of a driver should be done in a way that it is subjected to the claimed wattage for a long period of time over the frequency range in which it is intended to operate. I'm thinking, though, that pitfalls occur at both frequency extremes:
    * at high frequencies, the cone movement is negligible, so one tends to lose convective cooling of the coil;
    * at low frequencies, the cone movement gets very large (which is great for convective cooling), so the excursion limits may be encountered, thereby resulting in mechanical damage.

    The highest acceleration (which generates the internal forces you are concerned about) occurs at the highest frequencies, so I would think that if a driver can survive rated power continuously at its highest intended frequency, then it should be fine over its passband. Of course (as many of us have pointed out), one still has to be careful about overexcursion at extreme low frequencies, regardless of power input.
    - Mike
  16. frankencow150

    frankencow150 Guest

    Oct 17, 2001
    i have a small squier practie amp,would using disorton on that from a korg multi0effects pedal be O.K?