Bob Lee (QSC) Messages: 1792 Registered: April 2004 Location: Costa Mesa, California
Has No Life
Good catch. Yes, it may be well-intentioned but is based mostly on incorrect assertions.
"Most of the electrical energy is used up in the creation of mechanical energy.
"A very small amount of electrical energy remains in the voice coil in the form of heat, but it is dissipated by the air flow caused by the movement of the woofer cone."
Over 90% of the audio power delivered into a dynamic loudspeaker turns into heat. This is well documented.
"When a square wave is presented to the speaker, instead of the seamless back and forth motion of the cone, we get a different behavior.
"The cone moves out, pauses momentarily, moves back in, pauses momentarily, moves back out, pauses.. you get the idea.
"These pauses are heard as audible distortion, as the acoustical energy is literally cut up by the pauses.
"Of course, these pauses are exceptionally tiny, but during each one of the pauses a small amount of heat builds up in the voice coil because the lack of movement of the cone removes the cooling ability of constant air flow."
This story of clipping making the speaker cone "pause" and thus lose cooling is another long-disproven myth.
Greg Cameron Messages: 1832 Registered: April 2004 Location: Nevada City, CA
Has No Life
Yup, some bogus information. IIRC, square wave fed to a cone will actually cause the excursion to proceed during the "flat" portion of the waveform. IOW, I believe the motion is still "sinusoidal" and does not track the shape of the clipped waveform. Like JR says, "it's the POWAH!" 200 watt amp clipped hard produces up to 400 watts which will exceed the 250W rms rating of the driver. Simple enough.
John Roberts {JR} Messages: 10915 Registered: April 2004 Location: MS
Has No Life 10,000+
Yup... BS... Another self proclaimed junior expert who doesn't know what he doesn't know.
Driving a speaker with a square wave doesn't ever make it stand still, unless you drive it so far you hit the VC travel limits, and that has nothing to do with waveform shape.
TJ (Tom) Cornish Messages: 1091 Registered: April 2004 Location: Saint Paul, MN
Has No Life
Saying "underpowering" blows loudspeakers is at best an incomplete description, and probably closer to completely incorrect.
- First of all, it fails the obvious logic test. If you could truly blow up a speaker by supplying it too little power, speaker manufacturers would list "minimum SPL" and "minimum watts" - turning down the volume would blow things up. Obviously this is not the case.
We're then left with semantics - What the author is saying is that it's possible to get more than 200 watts out of a 200 watt amp if driven into clipping, and this can potentially damage loudspeakers whose program ratings are above the amp's "maximum" wattage. This is not underpowering, this isoverpowering. The formerly too small amp has now become too big.
The larger part of the fallacy is the implication that getting a larger amp will solve the problem. If the user is moronic enough to run a small amp into severe clipping, they are going to repeat the process with a larger amp and blow up their speaker even faster. The problem is expectation management - more commonly known as having enough rig for the gig.
Clipping doesn't automatically guarantee speaker distruction - you can square wave a 50 watt amp plugged into an 800 watt RMS speaker for a year and it will happily reproduce the square wave. Clipping only contributes to damaging speakers when the output of the clipped amp exceeds the driver's ability to handle this.
The interesting part of this article is the author left out one of the more valid parts of this argument - that is of blowing tweeters in passive boxes due to increased harmonic content which can be directly caused by clipping.
Greg Cameron Messages: 1832 Registered: April 2004 Location: Nevada City, CA
Has No Life
TJ (Tom) Cornish wrote on Tue, 16 March 2010 14:16
Wow - this apparently touched a nerve - lots of us typing in unison.
I think it's just been beaten to death to the point where most if not all the info is available right here on the LAB. So it really is unacceptable that false information should be posted as an article on a site where the people "in the know" are hanging around. It's a bit strange. All he had to do for research or confirmation was a search here.
Bennett Prescott Messages: 8924 Registered: August 2004 Location: Central CT
Has No Life
Now that articles are being written for PSW independent of Live Sound magazine, it appears that the technical editorial oversight is nonexistent.-- Bennett Prescott
Director of North American Sales ADRaudio d.o.o.
Cell: (518) 488-7190
"Give me 6dB and I shall move the world." -Archimedes
Bennett Prescott Messages: 8924 Registered: August 2004 Location: Central CT
Has No Life
John Murray, who is a real smart guy, edits the technical articles for Live Sound. Obviously he is not involved in those for PSW. Considering the little I get paid for Live Sound articles, I doubt there is much available for PSW writers which may also reflect onto the quality of articles there.-- Bennett Prescott
Director of North American Sales ADRaudio d.o.o.
Cell: (518) 488-7190
"Give me 6dB and I shall move the world." -Archimedes
There is no such thing as ‘RMS Power.’ No matter how often it is repeated, no matter what is intended, the term is technically incorrect. If it were not so, credible manufacturers of pro audio amplifiers and speakers would list ‘RMS Power’ in their spec sheets. A quick perusal of such manufacturers’ websites (QSC, Crown, JBL, EAW, EV, etc) will show otherwise. Unfortunately, many MI manufacturers (Mackie, Cerwin Vega, etc), and even some misguided posters on this forum, continue to propagate this mythical term.
Bob Lee at QSC authored a white paper on power amplifier basics, where he points out the incorrect ‘RMS Power’ term:
No flame intended here, but as we’re critiquing other people’s (not so) technical articles (and I agree with the overall message of these critiques), we should be careful not to err ourselves.
Bob Lee (QSC) Messages: 1792 Registered: April 2004 Location: Costa Mesa, California
Has No Life
I contacted Keith Clark, editor of PSW. He's pulled the article (pending a rewrite, revision, overhaul, or whatever it turns out to be). Bob Lee
Applications Engineer, Tech Services Group QSC Audio
Secretary, Audio Engineering Society www.linkedin.com/in/qscbob
frank kayser Messages: 378 Registered: July 2009 Location: DC
Has No Life
Sorry, guys.
I've read just about everything on speaker destruction using an underpowered amp driven to clipping being more likely to blow up a driver than a larger amp not driven to clipping. I have read the 2x or 3x amp power to the speaker rule. I understand that clipping produces a misshapen wave form.
I also read that article (now taken down) and I did notice that it was contrary to that posted here - of course this is basically an unmoderated (no offense to the moderators) board, and like other boards where "experts" hang, one tends to take posts here less seriously than "a published article" on the sponsoring web page. Seems harder to tell the sh*& from the shinola...
I still don't get it. Guess I'm just thick. I believe, in theory, that the clipped signal is the culprit in many driver failures. I guess my question after all the reading is why.
For example, a 200w rated speaker with a 150w amp driven into clipping produces, say, 250w. That would probably trash a driver, correct?
But it I were to take that same 200w speaker and drive it with a 600w amp to 250w that wouldn't trash the speaker?
Is it the waveform that is damaging, or the higher average power? Something else? Typical failure in the above situation would be overheated voice coil? "Uncontrolled" excursion?
Honestly, I've heard too much, and my mind is mush - I can't process the various views. I can't separate fact from fiction. Plainly, I don't get it. I believe it...
Maybe it would appropriate to make a sticky on the subject. I'd be willing to do it, but don't understand the subject well enough - kind of like this whole thread...
I'd appreciate any clarity, or being pointed to a trusted source to read.
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