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Clipping / Distortion / Speaker Damage?

Discussion in 'Amps and Cabs [BG]' started by Fangry, May 9, 2002.


  1. Fangry

    Fangry

    Apr 27, 2002
    Helsinki, Finland
    Ok, everybody's been saying how it's better to overpower a cab than to underpower (sic) it, and thus I'm in the process of getting a Sansamp RBI with a 1400W power amp :)

    BUT. If the worst damage to the speakers is done by clipping the amp and by doing so causing distortion, and if a clean signal is the only thing healthy to the speakers, what about distortion effects? I play in a metal band and usage of some kind of fuzz is crucial to being heard from under two loud guitars. Even studio engineers want to use distortion on the bass to make it audible.

    Am I killing my speakers by doing this?
     
  2. steve-o

    steve-o Guest

    Apr 17, 2002
    i don't think so.
    just the amp pushing to hard is what hurts your speakers.
    just my 2 cents sorry if i am wrong.
    Ampeg has there new amp that has a overdrive channel in it. you would think that they would be the first to know about it if it hurt speakers

    steve
     
  3. The type of distortion caused by overdriving speakers and that generated by fuzz are two entirely different things.

    By driving speakers too hard you are over driving an electro-mechanical system that's bound to fail sooner or later - sooner, probably. It's a similar idea to running your average family saloon car at full speed around a rally track: it won't last long. In any case, IMHO, the sound of overdriven speakers is very harsh and is akin to overdriving a tranny amp. Also IMHO there's absolutely no truth whatever in the idea that overdriving cabs is a good idea; it's one of those odd tales that gets passed between musicians and eventually most believe it.

    I suggest you contact Joris, MickeyD, Bgavin + other speaker experts on these boards for a fuller explanation.

    Fuzz acts on the signal at low levels. It alters the harmonic content of the signal by squaring the waveform in a special way (with kind-of rounded corners to a non-square peak). It's supposed to emulate the sound of an overdriven valve amp. Speakers will, more or less, faithfully respond to whatever signal the amp presents to them provided the speakers are operating within their design limits.

    Fuzz is OK. Thrashing speakers is not.

    John
     
  4. Fangry

    Fangry

    Apr 27, 2002
    Helsinki, Finland
    Thanks a lot.

    So I guess it's got more to do with signal levels than jagged waveforms.

    I'm not too crazy about using dist pedals but everyone's telling me to use one cos the engineer at the studio my band recorded at told us it's a must ;)
     
  5. FunkySpoo

    FunkySpoo Supporting Member

    Feb 6, 2002
    I'm no electrical engineer but from what I think I understand is that the signal from amp to speaker is a wave. When an amp is driven into clipping the tops and bottoms of the wave are "clipped" off. the clipped portion of the wave then builds up as heat in the speaker and this is what burns up the voice coils. Is that kind of in the ball park or am I way off base here? In a distortion effect unit there is no clipping and that's why it won't hurt your speakers
     
  6. 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 issue is power, not waveform. Pushing an amp into severe clipping makes it produce more power than it is rated for, and it also elevates the average power in the signal. It also sounds like crap.

    If that power is too much for the speaker to handle, the voice coil(s) will eventually overheat and either burn out or cause a mechanical failure.

    Thus, outrageously clipping a 50-watt amp driving a 500-watt speaker won't damage the speaker, but it sure won't sound good. OTOH, severely clipping a 200-watt amp driving a 300-watt speaker could cause speaker damage.

    The way to avoid problems is to have enough amplifier and speaker to get the sound levels you want without clipping.

    And yes, a distortion effect works by clipping (or simulating clipping) the signal at a low signal voltage, so it is not a danger to speakers unless you push the amp to produce more power than is safe for the speaker.
     
  7. FunkySpoo

    FunkySpoo Supporting Member

    Feb 6, 2002
     
  8. FunkySpoo

    FunkySpoo Supporting Member

    Feb 6, 2002
    Hey Bob, does your head just want to explode when you read something as stupid as I wrote?
     
  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
    LOL! No, compared to some phone calls I get (I had a guy once who didn't know what "input" and "output" mean), your message wasn't that bad. ;)
     
  10. Heres what I've heard about the difference between amp clipping and preamp/fuzz clipping, please correct as nessecart!:

    Fuzz clips the waveform - making more like a squarewave from a syntheziser. Overloading preamps etc also causes clipping of the audible waveform. Most fuzz boxes/premaps filter out very high/low content of frequencies.

    With clipped power amps - clipping of the non_audible signal can occur - presumably below 20hz above 5k or whatever. Don;t ask me if non audible signal is there all the time or not... the point is a lot of energy starts coming out of the amp which the speaker *cannot* convert into movement. Its converted into heat instead, and if theres enough of it the driver fries.

    Thus, a 50watt amp with heavy clipping *can* thrash a powerful speaker, it starts putting out electrical energy of a frequency that does not make the speaker move, the energy is then transduced into heat, not sound....

    this happens anyway at the edges of the speakers
    'range' ---- hi-power hi freqs into a woofer will make it heat up, it can't play them...

    so...the clipping you *can* hear is not what to be worried about, its the signal that you can't hear....


    Magman
     
  11. FunkySpoo

    FunkySpoo Supporting Member

    Feb 6, 2002
    Thanks, I was just repeating what I had read somewhere. Just goes to show how misinformation gets passed around. Thank the bass gods you're a regular here.
     
  12. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    From everything I've heard, this doesn't seem to be right. I don't see how you can clip a nonaudible signal if it wasn't already present in the signal coming to the amp, and I don't see how a bass, especially a 4-string, is gonna produce much signal below 20 Hz. If the bass doesn't produce that kind of sub 20 Hz signal, the amp can't clip it--it can't do anything with or to it.

    Bob's post reflects what I've heard, namely that the main problem is that clipping results in excessively high power output and elevates the average power delivered.

    Check out this link:

    http://www.rane.com/pdf/note128.pdf
     
  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
    If a "powerful speaker" means one rated at maybe 50 to 100 watts continuous power, then, yes, a heavily clipped 50-watt amp could thrash it. If it's a speaker meant to handle hundreds of watts of continuous power, no, it won't.

    Even in a square wave, which would be analogous to a very, very badly clipped signal, the fundamental (f) is still about 81% of the total power. The strongest harmonic above that would be the third (3 * f) at 1/9 the power of the fundamental, followed by the fifth (5 * f) at 1/25 the power of the fundamental, and so on.

    The power in each harmonic drops off quickly as you go up the series. Thus, harmonic power is not a significant factor in damaging woofers and subs, but it can put extra stress on tweeters and midranges. Also, speakers only convert about 2 to 3% of the power put into them into sound; the rest is wasted as heat. That's why whether the signal is of a frequency that the speaker can reproduce well is largely immaterial, unless you're talking about tones that are below the driver's safe frequency range, which can cause damage through overexcursion.

    I don't know what you mean by the "inaudible signal."
     
  14. CombatWombat

    CombatWombat

    May 5, 2002
    if you clip a solid state amp a lot, the signal is changed into DC. That fries the voice coils of your speakers
     
  15. 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, that is untrue. The signal is not changed into DC (if you get DC on your amp output, your problem is a defective amp, not clipping).
     
  16. >I don't know what you mean by the "inaudible >signal." [/B][/QUOTE]

    well.... I'm not sure where any signal not in the 20-20000hz is going to come from in the first place, so maybe I'm replying bad info here...

    but.... if I;ve got a cab with speakers that reproduce nothing above about 6k hz, then I put a 300 watt 15k hz sine wave through them, *all* of that energy is going to go into heat --- correct?
    while being inaudible....because the speaker can;t recreate it.

    SO.... is there no difference between a clipped power amp and a square wave of the same wattage regarding its effect on a speaker...
     
  17. 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 the speaker cabinet is rated at up to 6 kHz, that probably means it's 3 dB down at that frequency. At 15 kHz, it'll probably be around 8 dB down. The cone might be moving, but probably not as one piston. Nearly all of the power going into it will turn into heat. But even at 1 kHz, nearly all of the power going into it will turn into heat. And at 100 Hz, same thing.

    Of the same voltage.

    Let's say you've got an amp rated at 100 watts into an 8-ohm load. That means that the highest sine wave voltage it will put into the load before clipping starts is 28.2 volts rms. The peaks of the sine wave will be at 40 volts. So the amp will clip any signal that goes above 40 volts.

    Now you boost that signal way, way up so that you've got a 40-volt square wave. The power put into the 8-ohm load isn't 100 watts anymore, it's 200 watts.

    So that's what happens when you clip the amp. But you're not using continuous sine waves in music; you're playing bass, or you might be running other audio through a sound system. What's happening in between the clips could also be roasting your speaker(s). Without clipping, you might hit 100 watts with that same amp maybe 0.1% of the time (on peaks), and the average power might be down around 15 watts. But if you've got severe clipping, you could be hitting close to 200 watts maybe 20% of the time, and the average power in between is up to maybe 75 watts or higher. At that point, any musical sense to the signal will be pretty much obliterated by distortion. And unless the speaker is rated for more than, say, 150 watts, it will probably be obliterated, too.