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[Lester Seidenberg]

I have seen speakers blown up being under powered  and speakers fried being over powered.   What it usually boils down to is the wrong tool being used in an application, and usually that is the result of trying to save a few bucks on system design/installation.
Lester

[Steve M Smith]

It's too much energy in the coil which causes it to heat up and eventually fail.


Steve.

[Jeff Bankston]

In my 30 + years in the consumer electronics industry I find your statement that under powering speakers will not blow them to be inaccurate. I not only work with pro audio but sell and install home theater and car audio speakers. Many times I have had customers buy (against my advice) the biggest woofers available for their car yet skimp on a power amplifier and either buy an amp that is too small or buy one of the wonder amps on the market that offers 10,000 watts for $99.00 and come back with very nice woofers with very cooked voice coils. I've seen this scenario several times a year repeated over my many years in the industry. I once had a customer purchase the most expensive woofer I had in stock (A Punch Pro Series 12" subwoofer that I believe had a rating of 400 watts RMS). We tried to sell him an amplifier but he only wanted the speaker. He came back a week later with the speaker blown. The voice coil was completely locked up. I asked to see how he had hooked it up and what he was running the sub with. He took me to his car where I discovered that he had been driving the sub with one channel of his high powered in dash radio. I asked him to turn his radio up to the volume he usually listened at and he ran the volume up to maximum. He had managed to fry the voice coil of a 400 watt woofer with what was probably 12w of highly distorted power.
 I'm not saying that this guy or any of the other customers I've dealt with wouldn't have totally smoked their speakers with the recommended amount of power but I can say that I see and have seen many speakers come back as charred locked up blobs of nothing after being exposed to high levels of distortion over extended periods of time on amplifiers that were far below the rated power handling of the woofer.

under powered , over powered how doo ya know ? i built my first pa around 1971. RMS/Continious power and Peak power handling were the 2 ways amps and eventually speakers were rated. you have an amp rated 100 watts RMS/Continious at 8 ohms and a speaker rated 100 watts RMS/Continious at 8 ohms you had a perfect match. RMS/Continious became AES and PEAK power became "Program Power" which means double. over the years in order to BOOST HYPE amp builders used the 1K power rating to post there power. lots of speaker ratings became "music power", etc. QSC claims clipping doesnt blow speakers. back in the 70's and part of the 80's i use to go the concerts at the Mississippi colusium and would make my way to the desk where the amps normally were and the Crowns, AB , Phase Liniers , etc had clip lights glowing or meters pegged and i never knew of a blown speaker in that 10,000 seat arena during all the hard rock/heavy metal band concerts. some monitor amps went out one time but no speakers. i would talk to the sound guys after the show during load out. we use to crank the Dynaco 50/60 watt amps and turn the volume up even though they were wide open and the red/orange frame  Radio Shack 15" and 12" musical instrument speakers and cheap horns never blew, maybe the ears of those in the audience blew but no speakers. never blew any Altec voice of Theater speakers eaithe maxing out amps. i was talking to my ole bass player last week and he still has a pair of the old Atecs we used. i garuntee you that if clipping would destroy speakers my Marshall JCM800 2205 amps that use clipping diodes would have taken out 30 watt geetar speakers long ago. i dont trust the power ratings of car amps or cheap home amps or home theater amps. this stack in the foto is tri-amped and the 8 ohm woofer is rated for 1000 watts AES/RMS and is powered by a bridged qsc amp rated at 900 watts ohms and it is night and day louder than my landlords 2000 watt 3 speaker 800 dollar surround tv sound system.

p.s. its entirely possible that cheap amps that are run wide open pass dc current and that will blow speakers. you get what you pay for and home theater is ment to produce concert level sound.

ALSO ! to show you how stupid and ignorant the whole concept of underpowering blows speakers answer this question > if underpowering speakers blows then then how come the speakers dont blow when i have the power turned way down ? i repeat , if using too small an amp(underpowering) blows speakers then that means you would need to run the amp atr full power to not blow speakers. see how rediculous that is. imo pushing cheap amps to their limit and beyond "probably" causes them to send some DC current to the VC thereby frying it. Crown DC series amps are bad about that and they are professional grade and 100,000's of thousands were probably in use back in the day.

[TJ (Tom) Cornish]

I have seen speakers blown up being under powered  and speakers fried being over powered. 

I wish you guys would stop digging this hole - this is beyond tedious.

Form 1 of the "under-powering" myth: Running an amp into extreme clipping increases HF content of the signal, contributing to HF driver damage. 

This one is half-true - a square wave does have high-order harmonics that a sine wave doesn't.  HOWEVER: These harmonics are at much lower energy than the fundamental, and beyond the 3rd harmonic (which is likely still at least partially being reproduced by the LF driver) really don't represent that much power.  See this link for a graph: http://www.informit.com/articles/article.aspx?p=1374896&seqNum=7 

The more likely reason for tweeter failure is that as you continue turning the volume up, you start increasing the amount of legitimate signal in the HF band, which can exceed the relatively modest power capacity of the tweeter.  A 100w woofer may be paired with a 5w tweeter - something that a small amp - say 50w - can easily OVER-power.  With extreme HF content in the source, it's very possible to blow the tweeter even without clipping the "too small" amp.  In any case, a larger amp makes this problem WORSE, not better.

Form 2 of the "under-powering" myth: The shape of the waveform can cause speaker damage, square waves are bad for speakers, a too-small amp can blow LF drivers, however you want to phrase that.

This one isn't even half true, as there isn't some counter-intuitive factor buried here that confuses the situation. 

The shape of the waveform doesn't matter to the driver.  A common misconception is that the driver follows the shape of the waveform - if the signal is a square wave, then the driver will magically move infinitely fast from in to out, causing damage from "slamming".  This is not the case.  The driver and coil assembly have mass, and therefore have inertia to overcome, and can't move infinitely fast.  The waveform acts like a gas pedal in each direction - send a positive signal and the driver starts receiving a force that begins to change the direction and/or speed of the driver out.  Send a negative signal and the driver starts building energy to go in.  The greater the amplitude, the faster the driver movement.  The steeper the slope of the line, the faster the direction change is begun, subject to the driver's ability to follow the signal.

The mass of the driver assembly directly relates to the frequency range the driver can reproduce.  If the frequency of the signal is high, a heavy driver never finishes moving before getting orders to go the other way, and therefore little movement and little sound is produced.  This is the natural low-pass behavior of the driver.  The HF energy that hits the woofer, yet is too fast to translate into movement, is lost to heat; however that HF signal is low energy compared to the LF energy (see chart in above link), and isn't very significant.  Additionally, the impedance of drivers rises as frequency increases, so the driver accepts progressively less of the HF energy offered as frequency increases.

As an amp starts clipping, the power does continue to increase; a hard-clipped amplifier producing a square wave produces up to (depending on the capabilities of the amp) twice the power - 3dB more - than a sine wave of equal amplitude - the amp operating right up to clipping.  As most of this extra energy is dominated in the 3rd harmonic (3X the fundamental frequency), this new energy is likely still in the operating range of the LF driver, and is reproduced (and sounds like crap), and contributes to heat and excursion of the driver.

So, therefore then under-powering is real, then right?  Not really.  If we use a "correctly-powered" amp that's 3dB larger than the "under-powered" amp running to just before clipping, we're still putting 3dB more signal into the woofer; however the energy now is in the form of the intentional frequency rather than harmonic distortion.

Whether either this clipped signal or the unclipped louder signal from the larger amp will damage the driver depends totally on the capabilities of the driver.  A 100w amp run into full square wave into a driver rated for 3200 watts will run forever.  A 3200 watt amp run at -10dB into a 100 watt driver will let the smoke out.


At the end of the day, this is all that matters about powering speakers:

- For best performance, an amp that equals or slightly exceeds the program rating of your speakers is a good idea.  This is about utilizing the full capabilities of your speakers, not about speaker protection.
-  Depending on the relative capabilities of your speakers and your amps, extreme clipping may contribute to driver damage, or it may not.  Either way, clipping is bad.  Please don't do this - it makes your system sound like crap.
- If a person is dumb enough to ignore all warning signs and fry their system, giving them larger amps is like giving your nephew who totaled his Civic a Porsche. The only difference is death will come sooner and/or more spectacularly than before.
- Bring enough rig for the gig.

[Bob Burke]

Thanks for that explanation, Mr. C.  I have been operating under the “low-power blows speakers” fallacy for a long time. So the determining factor is clipping, regardless of power. I never get anywhere near clipping with my little rigs – an advantage of being a duo.

[Art Welter]

Thanks for that explanation, Mr. C.  I have been operating under the “low-power blows speakers” fallacy for a long time. So the determining factor is clipping, regardless of power. I never get anywhere near clipping with my little rigs – an advantage of being a duo.

No, the determining factor is too much average power burns speaker coils.
A severely clipped amp can put out 3 dB or more average power than it would if not clipped, as well as much of the increase in clipped power is high frequency harmonics which are more likely to burn tweeters than woofers, as tweeters have lighter voice coils that heat and burn faster than woofers.

[ProSoundWeb Community]