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Running Distortion - Amp Risks

#61
Fuzzbass said:
I don't normally post comments from other forums here, but the synchronicity is too much to ignore. Anyone care to respond? :ninja:
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Nonsense! How's that for a response? :D

Now that I've got the saucy answer out of the way, let me take the argument apart: :p

Assuming a speaker that can truly dissipate 200W here.

What the poster said about heating power is true. A pure square wave has the same heating power as DC which is twice the heating power of a sine wave of the same amplitude. So a pure square wave into a 4 Ohm speaker dissipating 20W will be about 2.25A continuous through the coil (i.e. 9V peak voltage). Fair enough. What about a 9V RMS sine wave? That has an effective continuous current of 2.25A throught the voice coil and a continuous power of 20W. RMS values are the DC equivalents of AC waveforms.

Why would the 2.25A continuous from the square wave melt the voicecoil while the 2.25A continuous from the sine wave not do it?

Cooling is not greatly affected by waveform. In my experiments I found no noticeable difference in speaker cooling efficiency between pure square waves and pure sine waves from a tone generator (with same average power). Cooling is significantly derated if the coil comes out of the gap though.

Didn't I say I was going to stay out of this? Ah Jeez........ ;)
 
#64
greenboy said:
Was that a YES or a NO!!!??!??!

I'm anxious to get an answer so I can sell all my distortion and overdrive pedals to some sucker before all my cabs blow up!!!!

HELP!!!!!!!!!111111
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I have different problem, when I play good clean non distorted opera music at high volumes then my wine glasses shatter. Would they not shatter if I added distortion?
:-)
 
#66
Mark Reccord said:
Amps don't ever produce real square waves either..... What everyone seems to forget is that in both amp clipping and in distortion effects, the portion of the input wave below the clip point is unaffected, so the output mimics the input below the rail voltage (or the artificial diode clipping point). Yes, distortion effects do tend to have filters that cut out a lot of the higher harmonics, etc. but the general mechanism is the same.
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But it really doesn't matter, since when they are even a few dB into clipping, the average power output starts heading up. The exact squareness isn't a big deal.

The general waveform of the bass is very unsymmetrical and loaded with harmonics. So even a fairly small amount of clipping *can* start the average power up in a hurry. And there is no EQ to modify the wave, it is flat-topped going to the speaker.

By contrast, the distortion pedal continues with an eq'd, usually somewhat peaky waveform. That generally has a much lower peak-to-average ratio than even a sort-of square wave, and is almost independent of the amount of distortion (overdrive) past the threshold of distortion.


Your second last point is what I always try to drive home in these threads. The point is that the waveform in and of itself is not what causes problems, it's the average power incident on the driver.... But you know this. :D
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Yes I do :D .

But the waveform affects the power available, since the square or semi-square wave has a average equal to or close to equal to the peak.

An eq'd square wave does not, accounting for the difference in effect.

I'd not worry too much about a pedal. Maybe cut the power amp to speaker rating ratio from 3 or 4 to 1 down to maybe 2 to 1, possibly lower if you really turn up.

So a 1200W amp might then want a 600W to 800W (or more) rated speaker, if you are going to push it with a distortion pedal. (and I may not want to hear your band!)
 
#67
Jerrold Tiers said:
But it really doesn't matter, since when they are even a few dB into clipping, the average power output starts heading up. The exact squareness isn't a big deal.

The general waveform of the bass is very unsymmetrical and loaded with harmonics. So even a fairly small amount of clipping *can* start the average power up in a hurry. And there is no EQ to modify the wave, it is flat-topped going to the speaker.
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At what point does a clipped wave become a threat to a woofer?
 
#68
A couple of days ago I did an extremely quick'n'dirty Google search: "can square waves blow speakers". I examined the top three results that impressed me as unbiased, well-supported, scientific. Fortunately they happened to be the top three in the search list. It was interesting that none mentioned danger to woofers from low-power clipped signals... they focused on tweeter damage.

Again, this was a very quick search, and three search hits don't remotely count as a consensus. Rane was the only site I recognized... I've no idea who the other two guys are. Still, I'd like to submit them for discussion/comment (if anyone feels like doing so). Here are links and excerpts.

<P>

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Title: Too Little Power Blowing Speakers

http://www.bcae1.com/2ltlpwr.htm

Author's conclusion re woofers:

* If your speakers are capable of handling significantly more than your amplifier can produce, driving them with a clipped signal will not likely hurt them.
* If the speakers can handle 3 or 4 times the power that your amplifier can produce, there's virtually no way to damage your speakers (no matter how clipped the signal is).
* If your speakers are rated for the same power handling as your amplifier is capable of producing cleanly, driving them with a clipped signal for extended periods of time may cause speaker damage and/or premature failure.
* If your speakers are rated for the same power handling as your amplifier is capable of producing cleanly, driving them with a square wave signal for extended periods of time will likely cause speaker damage.

-----------------------
Title: Power Amplifier Clipping and its Effects on Loudspeakers

[Invalid or Expired Link Removed]

(no excerpt - mainly concerns threat to tweeters)

-----------------------
Title: Speaker Damage

Link Removed

Excerpts:
This is the old "how does clipping blow up a woofer" problem. I know that woofers rarely blow up, even with severe overload, and in essence they seem to be immune (although that might overstate things a bit!). This is (or would be) true, but for one small detail. Few speakers (including woofers) can tolerate their full rated power on a continuous basis. The rating is more for "amplifier power" than speaker power.

....

There are - naturally - limits. A 10W woofer won't last long with a 300W amp driving it at anywhere near full power on transients, but a 100W woofer will last forever with a 10W amp in permanent overload. Some common sense must be applied, but a typical 100W woofer will probably last forever with a 200W amp used sensibly.

The comment above is aimed more at the risk of tweeter damage, but it can happen with midrange drivers and woofers too, given the right (or wrong) set of circumstances. One issue with many modern recordings is excessive compression, and this can increase the average power level dramatically, even before amp clipping.
 
#69
A square wave of the same peak to peak voltage would be 2x the power rating of a sine wave. For a 100W amp (sine wave rms), if it was generating a perfect square wave it would be putting out 200w. If you have a 200w rated in the box woofer you can't blow it out with 100w amp.

The Rane article is key to a few misnomers being tossed around. Harshness from clipping isn't as much from the clipped signal as it's from the high frequencies of the input signal becoming unproportionately louder.

You can hear some sine clipping .wav files on the first link above. Watch the bars your wav player spectrum display and you'll see clipping doesn't add as much highs as some would believe.
 
#72
DopplerShift said:
Ummm

Revisting this thread and reading through the replies has left me more than confused. I guess I asked a question that I am technically unable to understand the answer.

Suffice it to say that I'll distort my bass and see what happens. Thanks for the replies. :D
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Ah, sorry... Sometimes us tech types get a bit carried away:

Simple answer: There's not much risk of damaging anything using distortion effects, unless you're running your rig really hard to begin with. I wouldn't worry about it too much with your setup.
 

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