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Clipping or Too Much Power?

Pandovski said:
Whats the theory? We are eager minds willing to learn in this thread.



You are both wrong.
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I probably don't want to know about the trannies you were talking about then.:D

It's only a theory of mine and I can't prove it, so I'm not sure I want to debate what I think but can't prove.
 
In a linear amplifier the limit on how much power is the size of the power transformer, bridge rectifier and power supply capacitors. These parts supply the voltage for the power supply 'rails'. Higher power amps may have rail voltages as high as 90 or more volts. The better the amp design the 'stiffer' the voltage rails will be and they will sag or drop less when the amp is at full power or beyond if the speaker has impedance dips.
When an amplifier is 'clipped' the musical sine wave, which is certainly AC, will exceed the peak power supply rail voltages. In other words the amplitude of the sine wave will be higher or lower than the rail voltage.
This flat section is not AC but the DC rail voltage so clipping an amp will make for a flat DC component at the top and bottom of the sine wave. Woofers do not like DC as this is excess heat in the voice coil that will not be dissipated as cone movement.
The solution to all of these problems is a higher powered amp that will never run out of power or an amp that will not allow the peak to exceed the rail voltage.

Thanks,
Ron-C
 
Very nice Ron. I understood it clearly. :)

What happens with tube amps or chip amps when they clip?
th_smiley-raising-waving-hand.gif


Thanks.
 
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There's a specific answer for specific conditions, but as usual everybody wants a generalization. Too much power will blow a tweeter. That power can come in the form of perfectly clean highs, from a big amp, at a very high level, or it can some as a bunch of high frequency junk as a result of hard clipping. What actually happens depends on the robustness of the tweeter and the drive conditions. IMO, there's no rule that always applies. In either case the SQ is probably so bad that it should be taken as a warning.
 
89grand said:
Well, I don't believe it's possible to damage a speaker from under powering it, but as far as over powering a speaker, either excursion limits are exceeded or thermal limits are. Speaker can only move so far and can only dissipate so much heat. Over powering a speaker to the point of damage exceeded one or both of those. It's not DC and it's not clipping, it's a thermal or excursion issue.

I have a theory as to why smaller amps seem to be responsible for more tweeter deaths, but it still ends up being an over powering problem, and not related to clipping, although clipping is probably present when it happens. I do not have the test equipment to prove my theory, but I believe it's likely to be the case of damage.
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I think it's best explained in this tech letter from JBL.
http://www.jblpro.com/BackOffice/ProductAttachments/lowpower.pdf
But, as you already know a good 40% here will still subscribe to the flat earth theory.
 
Pandovski said:
Overpowering speakers with too powerful amplifier means the amp is sending short but too large bursts of DC voltage
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Nonsense.

Amplifiers running within their operating range do not send "bursts of DC". My VTL tube amps are incapable of sending DC.
 
I'll go ahead and throw it out there I guess, but remember, it's a theory.:D

I'm also going to simplify this a bit with some generalizations in regards to power output in relation to frequency since there are too many variable to be exact, different music etc.

Let's take a typical 3 way loudspeaker rated for 120 watts and a typical 100wpc SS amp. In that speaker, the woofer may be able to handle 120 watts hence the rating of the speaker system, but the midrange won't handle 120 watts, and the tweeter definitely won't, it might only handle maybe 15 watts at the most. It doesn't need to though because the tweeter typically uses about 10% or so of the overall power the amplifier is delivering at any given time. If the amp is playing at a level that requires a few watts on average with peaks of say 30 watts, the tweeter would be receiving well under a watt on average to right around 3 watts on peaks. No problem, the tweeter can handle 10-15 watts (within it's designed frequency range).

Lets say you crank the amp up to it's unclipped maximum and it's delivering 100 watts on peaks, still no problem, the woofer can handle it and the tweeter can handle 15 watts and it's getting around 10 watts on these same peaks.

Now, one of the things I've always noticed is that even before audible clipping seems to be present, I'll start hearing thinness to the overall frequency balance when I'm pushing an amp too hard. I wondered why it sounded thin, less bass, and more mids and treble, even though I didn't hear any obvious distortion. My theory is this: If an amplifier reaches it's maximum output voltage (wattage) it's going to do it at bass frequencies first, but the amp is still capable of producing more power at higher frequencies.

Remember the higher in frequency the tones are, the less power they require, so up until the amp starts to run out of steam, the tweeter is getting but a fraction of the power and is well within its comfort zone. I maintain that once the amp reaches it's limit in output power into bass frequencies, if one drives the volume control more and more, the amp ceases to produce more power into the woofer, but can continue to increase in level at higher frequencies, and I believe that is A: The cause of thin sound, since the bass cannot get any louder, but the mids and tweeters can, and B: Is also the cause of tweeter death as now the tweeter, instead of the typical consumption of 10% of the overall power may now be getting 20, 30% or possible even more, of the power depending on just much further one continues cranking the volume control, so the tweeter is getting 20 or 30 or even more watts of power on peaks, well past it's design limit.

I don't believe clipping in itself has anything to do with tweeter damage, as you'd be able to kill a tweeter with a clipped preamp otherwise. I think clipping is often present when my theory starts happening and therefore it's believed that clipping caused the damage, but it's not the cause of the damage. I can also see, if my theory rings true, why bigger amps seem less involved in speaker damage since you'll maintain the 10% power ratio to the tweeters at higher overall volume levels, and it'd take a 300wpc amp driven to it's limit before it reached the same power output into the tweeters that the 100 watt amp driven beyond its limits can do.

One final note: A clipped wave form viewed on a spectrum analyzer may look like DC, but it isn't

OK, flame away y'all!:D
 
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One more thing, so it doesn't get misinterpreted from the above post. I still think an amp has to be somewhat powerful to blow a tweeter. It isn't going to happen with a 5 wpc amp no matter how hard it's clipping. So an amp can be too small to blow drivers and an amp can be so powerful it can do it with or without the non-issue of clipping.
 
89grand said:
One more thing, so it doesn't get misinterpreted from the above post. I still think an amp has to be somewhat powerful to blow a tweeter. It isn't going to happen with a 5 wpc amp no matter how hard it's clipping. So an amp can be too small to blow drivers and an amp can be so powerful it can do it with or without the non-issue of clipping.
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exactly how i see it but the popular wisdom seems to preach the contrary.
 
89grand said:
One more thing, so it doesn't get misinterpreted from the above post. I still think an amp has to be somewhat powerful to blow a tweeter. It isn't going to happen with a 5 wpc amp no matter how hard it's clipping. So an amp can be too small to blow drivers and an amp can be so powerful it can do it with or without the non-issue of clipping.
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Well I'm impressed with it. Lets hear what the people with actual knowledge have to comment. :boring:
 
I had an integrated amp with some electronic gremlins that would occasionally see fit to turn itself up to maximum volume. It's output was specified as 120wpc and my speakers at the time were JM Lab Cobalt 807 which had a specified maximum of something like 75w. When the volume cranked itself the amp seemed to be clipping as opposed to the speakers reaching the maximum of their excursions, etc., but I do remember it sounding absolutely horrific. Thankfully the speakers were never damaged (apparently Focal makes some robust drivers) and the naughty amp was exorcised from my system.
 
89grand said:
No, that's a myth. If an amplifier has not failed, it will not send DC no matter how much it's being clipped.
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But isn't a clipped audio signal merely an approximation of a square wave? Squarewaves are in essense bursts of dc voltage, alternating the polarity every now and again, with the amplitude of the signal being the voltage applied.

Draw a sine wave of some frequency and some amplitude. The area under the curve represents the power seen at the speaker, the height of the wave form is the potential of the signal - the voltage sent by the amplifier. Now on the same scale, superimpose a drawing of a clipped wave of the same amplitude, and the same frequency. Note the difference in area of the two wave forms. The 'square' wave sends much more energy to the speaker for a given amplitude, and I believe this is what causes speaker failures, usually tweeters. Heats up the voicecoils and burns 'em up. In essence overpowering them, not the distortion itself, per se. I wonder if this is what Mr. Kantor and others mean? I have not read Mr.Kantors thoughts on the subject, but would like to. David, could you point me to some reading?
 
When you pass too much current through a wire or coil (voice coil) it burns. Whether it's in a speaker or not. I don't think anyone will argue this. As for clipping causing it the only way this would be possible is if the amp was really passing DC which is unlikely especially since most amps would go into protect before that happened. If a distorted signal fried speakers every guitar amp ever would have blown speakers.

I could see rare occasions of an amp passing DC and frying a voice coil. I just fixed a powered sub that had shorted FET outputs AND a blown woofer. It's possible the woofer got blown right after the outputs shorted and it passed DC before the protection circuit kicked in. More likely though someone overpowered it, fried the voice coil and created a 0 ohm load that caused the amp to blow.

I think both are possible but one is by FAR the most common.
 
So it comes down to either own fleawatt amp or pair of monoblocks. Anything in-between will kill tweeters when a Crescendo explodes in a tune.
 
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