Okay.......*** Sweetwater said......

[wcriley]

Sigh....there are always exceptions. I have blown speakers with over driving a low powered amp. So, I guess we are even.

This completely sidesteps the intent of my post which was: square waves, in and of themselves, no matter for what length of time, will not fry a driver.

If you've blown drivers by overdriving an amp, one of two things happened:
You exceeded the excursion limitations of the drivers.
Or...
You exceeded the thermal limitations because the distorted signal had a higher average voltage than the voice coil could handle.

In either case the problem was too much power. The shape of the wave, in and of itself, had nothing to do with it.

 

[Quickie]

This completely sidesteps the intent of my post which was: square waves, in and of themselves, no matter for what length of time, will not fry a driver.

If you've blown drivers by overdriving an amp, one of two things happened:
You exceeded the excursion limitations of the drivers.
Or...
You exceeded the thermal limitations because the distorted signal had a higher average voltage than the voice coil could handle.

In either case the problem was too much power. The shape of the wave, in and of itself, had nothing to do with it.

As you wish.

 

[KJung]

From the information I posted by different authors, under powering a speaker cabinet with a distorting amp is bad, hmmmk?

I think your term 'underpowering' and using the power rating of a cab to define if an amp is underpowered or not is what is getting you into trouble.

Is a 100 watt amp going into a thermally rated 400 watt cab 'less underpowered' than the same amp going into a thermally rated 1000 watt cab? Think about it.

Yes, if you do really stupid things with any amp, regardless of the power rating of the amp and cab, you can damage a speaker (although it is usually due to blasting through the excursion limits, cone creasing, etc. versus burning out the voicecoil... i.e., it has NOTHING to do with the relative power output and suggested maximum power input rating of the amp and cab). However, this has little to do with the rating of a power amp relative to the thermal rating of a cabinet.

 

[Downunderwonder]

As you wish.

Coil sees voltage "+1", accelerates cone, then sees voltage -1, descelerates the cone the other way. The driver doesn't care if it gets a gradually changing or abruptly changing voltage.

This is what I take from Mr Bill. Only one of you can be correct, I vote Bill.

 

[Vanceman]

There's got to be a better way to explain this to people. What's really happening is overpowering, but because most of us didn't know that our 300 watt amp was capable of pushing out 600 watts (for example) when distorting/clipping. If we were using a 600 watt amp, we probably would not have to push it into clipping.

So, we were "underpowered" at 300 watts, and blew the speaker. What do you think?

And yes, you can push square wave through a round cone if you use a big enough hammer.

 

[James Judson]

Under powering a speaker is a myth, but. If you read Bills explaination it quite clear. A square wave has more average power than a sine wave.

A sine wave has 70 % (RMS) of the heating capacity of DC. Can someone tell me what the heating capacity of a square wave has??? Looks to me that a square wave (yes its not DC) should have the same heating capacity as DC (minus the cooling effect of speaker movement).

My conclusion is an amp running clean is putting out less power with a clean signal than the same amp pushed into full clipping. So the underpowering a speaker could blow speakers thing is really mislabeled. Should be under powering your speakers could cause failures by over power them. Not very likely at several hundred watts like most of us use. More likely if your pushing several thousand watts like the PA guy.

Some one should get "mythbusters" to prove me right or wrong.

 

[Horny Toad]

Some one should get "mythbusters" to prove me right or wrong.

If Kari Byron is doing the experiment, I'm tuning in.

 

[aborgman]

You are correct that you can blow a tweeter in a number of ways, especially if the tweeter circuit has no protection. However, running a severly clipped signal into a tweeter can do similar damage.

Yes, and the damage it does is due to... overpowering.

The severely clipped signal has a lot of high frequency content - way more than normal signal - and therefore has excessive power that blows the tweeter.

 

[billfitzmaurice]

Yes, and the damage it does is due to... overpowering.

The severely clipped signal has a lot of high frequency content - way more than normal signal - and therefore has excessive power that blows the tweeter.

+1. Those who understand how amps and speakers work are aware of this. Those who argue otherwise don't know what their talking about. Those who make post after post arguing otherwise deserve a spot on your Iggy list, as all they're doing is wasting everyone's time.

 

[nashvillebill]

One day I'll make a video of a sig gen pushing square waves through a tweeter just to show that the shape of the waveform does NOT automatically toast a tweeter.

It's excessive power that fries them!

 

[KJung]

Yes, and the damage it does is due to... overpowering.

The severely clipped signal has a lot of high frequency content - way more than normal signal - and therefore has excessive power that blows the tweeter.

+1 I think again the confusion with the tweeter thing is that when pushing an amp beyond its spec's hard, you literally 'overpower' the tweeter with that nasty clipped high frequency signal. Hence the 'oxymoron' that was described..... in the case of a tweeter, using an 'underpowered amp', NOT as defined by the power rating of the cab, but by the volume needs of the gig, can result in bad things happening to a tweeter without a protection circuit.

+1 all the way, and again, woofers won't be impacted.

 

[billfitzmaurice]

One day I'll make a video of a sig gen pushing square waves through a tweeter just to show that the shape of the waveform does NOT automatically toast a tweeter.

It's excessive power that fries them!

While you're at it do the same with a 6 ohm resistor in series with a 1mH inductor, which approximates the load presented by the average woofer. The square wave of the input won't be a square wave at the output due to the lowpass action of the inductor filtering the high harmonics, explaining why woofers are unaffected by the higher power density of the square wave. Here again those who understand how amps and speakers work will know exactly what I'm taking about, and those who don't know exactly what I'm talking about have no business offering opinions based purely on a fairy tale.

 

[JHAz]

Seems to me that if you can run a square wave, at low power, into a speaker and not fry it, that shows that square waves don't fry speakers. I'd expect that if a particular square wave will kill a particular tweeter sine wave in the tweeter's pass band with the same average power also would kill the tweeter.

In the 90s I bought a midlevel set of JBL PA speakers, and the manual advised using amps rated higher than the speakers' power ratings, to avoid overpowering the tweeters through distortion. But I didn't fully understand it and thought, for a while there, that the clipped waveform was the problem. OF course, simply thinking about pushing the crap out of my tube guitar amp, micing it into a PA, and not killing the PA should have led me back to the straight and narrow, but it took a while.

With PAs, especially, there are a couple of human factors that lead to distorted power amps and dead tweeters. First, as I understand it, distorted sound "sounds louder" than nondistorted sound at the same SPL. So if you want to feel you're rockin' the house, you push into distortion without even thinking about it. Second, we often find ourselves playing in settings where at least some of the participants are drinking (the demon rum, I mean). It's pretty well established, AFAIK, that when we drink, our hearing becomes less acute. So the PA needs to be louder during the 3d set to seem as loud as it was in the first set, to our customers and perhaps some of our bandmembers.

So if it sounds louder when distorted, and sounds quieter after a few beers, as the night rolls on there's a real tendency to push well into distortion.

Amps don't stop making more power at their rated power. Power is always rated versus a level of distortion even when the manufacturer doesn't specify it that way. Every amp I know of will stay relatively low in distortion until it reaches a "breaking point" or "knee" where a little added power adds quite a bit of distortion. (look at the "measurements" in a power amp review at Stereophile.com to see this, if you haven't before). Most amps are rated somewhere on that fast-rising part if the distortion-versus power matrix, so when you add a relatively little extra power above the rated power, you get a lot more distortion, but power will keep going up well past the rated power level.

 

[aborgman]

While you're at it do the same with a 6 ohm resistor in series with a 1mH inductor, which approximates the load presented by the average woofer. The square wave of the input won't be a square wave at the output due to the lowpass action of the inductor filtering the high harmonics, explaining why woofers are unaffected by the higher power density of the square wave. Here again those who understand how amps and speakers work will know exactly what I'm taking about, and those who don't know exactly what I'm talking about have no business offering opinions based purely on a fairy tale.

Yeah, that.

 

[MarkA]

I've read through this thread and the Fitzmaurice link. Let me summarize the salient points as I understand them, and y'all let me know if I misstep.

1) Using a 100W head within its limits (not clipping) into a cab that can handle 1000W won't damage the cab. This seems obvious -- it's like running a 1000W head with the volume turned down.

2) If you push a 100W head into hard (square wave or something approaching it) clipping, attempting to get more out of it than it can reasonably give, you might actually be getting more like 200W of output from it. Your 1000W cab should still be safe (even if it sounds like crap), but you might well blow or fry a cab that can only safely handle 150W, with the 200-ish Watts you're getting from your 100W-rated head. (To say nothing of what prolonged use like this might do to your head.)

3) In the above case of the clipped 100W head (putting out 200-ish watts) and the 150W cab, you'd be better off with with a 200W head run near, but not at, its clean-power-potential, putting 150 Watts into the 150W cab.

4) "Underpowering" is a term that's used inconsistently. You can't damage a speaker component by giving it "too little power," but if you use an amp that can't give you enough clean juice for the job at hand, push it to clipping, and in the process of clipping it generate more power than your speakers can safely handle, whether thermally or mechanically, then, yes, you could bust something. (If the clipped output is still below what your speakers can handle, though, it'll just sound bad -- without hurting them.) You could, under the right circumstances, then, get into trouble using an "underpowered amp" (even though "too little power" is NOT what's damaging your speakers). I think some of the confusion stems from that.

5) A square (fully clipped) wave has a lot of high-frequency content -- if too much gets to your tweeter, it could be damaged (because of too much power to the tweeter), even if the rest of the speaker components are okay. (You could run into a similar problem with an envelope filter used at extreme settings, too, right?)

6) A square wave's average power = its peak power. More average power = more heat generated than with a "musical" wave of the same peak power (where its average power is lower -- think of plucking or slapping notes on your bass). If the average power/heat generated is more than your speakers can handle, then, trouble. Otherwise, simply bad sound.

7) Thermal power handling is thermal power handling. Mechanical is influenced by your cabs, not just the drivers in them.

Am I missing anything? This is for my own understanding as much as anything. A year ago, I thought I NEEDED at least a 1000W head for my 1000W rated cab, both to use it to its potential (now I think actually putting 1000W into it would be a bad idea) and to avoid damaging it through clipping.

 

[billfitzmaurice]

Am I missing anything?

Nothing of consequence.

 

[B-string]

Pretty darn close MarkA!

 

[MarkA]

Thank you, gentlemen.

Re. the photo posted above... *sigh*. It made it hard to think about... you know... whatever.

 

[GrinningMouth88]

I've read through this thread and the Fitzmaurice link. Let me summarize the salient points as I understand them, and y'all let me know if I misstep.

1) Using a 100W head within its limits (not clipping) into a cab that can handle 1000W won't damage the cab. This seems obvious -- it's like running a 1000W head with the volume turned down.

2) If you push a 100W head into hard (square wave or something approaching it) clipping, attempting to get more out of it than it can reasonably give, you might actually be getting more like 200W of output from it. Your 1000W cab should still be safe (even if it sounds like crap), but you might well blow or fry a cab that can only safely handle 150W, with the 200-ish Watts you're getting from your 100W-rated head. (To say nothing of what prolonged use like this might do to your head.)

3) In the above case of the clipped 100W head (putting out 200-ish watts) and the 150W cab, you'd be better off with with a 200W head run near, but not at, its clean-power-potential, putting 150 Watts into the 150W cab.

4) "Underpowering" is a term that's used inconsistently. You can't damage a speaker component by giving it "too little power," but if you use an amp that can't give you enough clean juice for the job at hand, push it to clipping, and in the process of clipping it generate more power than your speakers can safely handle, whether thermally or mechanically, then, yes, you could bust something. (If the clipped output is still below what your speakers can handle, though, it'll just sound bad -- without hurting them.) You could, under the right circumstances, then, get into trouble using an "underpowered amp" (even though "too little power" is NOT what's damaging your speakers). I think some of the confusion stems from that.

5) A square (fully clipped) wave has a lot of high-frequency content -- if too much gets to your tweeter, it could be damaged (because of too much power to the tweeter), even if the rest of the speaker components are okay. (You could run into a similar problem with an envelope filter used at extreme settings, too, right?)

6) A square wave's average power = its peak power. More average power = more heat generated than with a "musical" wave of the same peak power (where its average power is lower -- think of plucking or slapping notes on your bass). If the average power/heat generated is more than your speakers can handle, then, trouble. Otherwise, simply bad sound.

7) Thermal power handling is thermal power handling. Mechanical is influenced by your cabs, not just the drivers in them.

Am I missing anything? This is for my own understanding as much as anything. A year ago, I thought I NEEDED at least a 1000W head for my 1000W rated cab, both to use it to its potential (now I think actually putting 1000W into it would be a bad idea) and to avoid damaging it through clipping.

Good man, i think that about sums up everything i've learned from explanations by mr. maurice and others who seem knowledgeable. Nice to see it laid out in front of me. It seems in some cases it's possibly a good thing to have a much higher rated cab, especially if you are running a sansamp, distortion pedals, sonic maximizer, etc.