effect of underpowering a cab?

[JimmyM]

No, they don't. No offense intended, but that's pure piffel. Read the FAQ, this dead horse has been beat so many times it's verging on the ridiculous.

Why is this subject here again? Where's a Mod when you need a topic shut down!

obviously there's a need for topics like this one because so many people STILL have no clue. i don't see why these topics keep getting shut down. the more they get shut down, the less the info gets out.

 

[Vanceman]

Speaking of destructive testing, it would be cool to put in your stage show something like when Marty Mcfly plugs into the giant amp/speaker at Doc's house, and the things blows up. Is there a possibility of amp damage when a cab blows/catches fire?

 

[billfitzmaurice]

obviously there's a need for topics like this one because so many people STILL have no clue. .

Isn't the purpose of the FAQ to answer Frequently Asked Questions? And where it comes to frequency this old chestnut is right up at the top of the list.

 

[JimmyM]

Isn't the purpose of the FAQ to answer Frequently Asked Questions? And where it comes to frequency this old chestnut is right up at the top of the list.

bill, i would think you've been around enough to know that nobody reads the faq's

 

[B-string]

We have FAQ's????? They should place them right on top so everyone would see them ..oh wait.....

 

[okcrum]

We have FAQ's????? They should place them right on top so everyone would see them ..oh wait.....

QED. Also .sig worthy. A double winner, ladies and gentlemen.

 

[Alex1984]

Would now be too late for the words "I come in peace..."?

Hmm, that was what the PA guy from a local music store described. Not trying to pin the blame on someone, so I'm gonna say what I took in from our conversations:

First, this is not a defence for my ignorance, I just want to exchange my understanding and see which part of it went wrong.

From what I understood, when the amp clips, it results in a large movement over relatively short period of time. The speaker ends up moving in pulses rather than a smooth continuous motion.

Mathematically, wouldn't a severely-clipped signal also makes the slope of the input waveform much steeper? If so, this'd call for the speaker to move in such a way similar to a large high frequency signal that the driver may not handle well. Although the same can be said about high frequency transients, they normally won't be as large.

Although comparing the outputs of bass amps and PA power amps to simple waveforms is a drastic oversimplification. But it made sense to me that sudden accelerations and decelerations applied over extended periods of time cannot be a good thing for the cone.

 

[Bob Lee (QSC)]

Uh, no.

If you want to learn about loudspeakera and cone motion, that PA guy is not the one to learn it from.

 

[Alex1984]

Would you be able to tell me a little bit about how they work?

 

[Bob Lee (QSC)]

Keep in mind that a loudspeaker is a linear motor, and voltage applied across it causes a current to flow, which interacts with the magnet to create a force.

When you apply a constant DC voltage across a motor does it stop? No. So why would the flat top of a clipped signal cause the loudspeaker to stop moving? Answer: it doesn't. It is just a constant accelerative force for that minuscule fraction of a second.

Two things blow loudspeakers: excessive power (thermal failure) and overexcursion (mechanical damage--e.g., bottoming out--from too much low-frequency energy).

 

[Alex1984]

Oh, another thing I wasn't sure about... How are tube amps able to supply the same power to any load? And if it's capable of doing that, why do they need the 4/8/16 switch behind them?

Our guitarists also say the same thing, but I still can't wrap my head around it. How does it work?

 

[Korladis]

Don't speakers normally move in pulses? When I play music on my stereo, the speakers certainly seem to be pulsing.

 

[Korladis]

Oh, another thing I wasn't sure about... How are tube amps able to supply the same power to any load? And if it's capable of doing that, why do they need the 4/8/16 switch behind them?

Tube amps are dumb. They don't know what impedence is there unless you tell them. That's what the switch is for.

 

[DukeLeJeune]

It's heat that fries voice coils, not a specific waveform.

If the voice coil gets hot enough, something bad will happen (glue melts, metal deforms, voice coil former ignites, magic smoke escapes, atoms split, known universe collapses into a singularity, Chuck Norris loses a fight, whatever). A big enough megazap of power can fry a voice coil virtually intantaneously, or a steady application of more heat than it can dissipate over time will do the same thing.

A high power amp can zap the voice coil, or slow-cook it. A low powered amp's only hope to kill the speaker and get the rest of the night off is the slow-cook. Here's how that can happen:

The more deeply an amp is driven into clipping, the higher the *average* power it's putting to the voice coil is. So if an amp is powerful to put out a distorted waveform whose average power level exceeds the thermal capacity of the speaker, it can theoretically kill the speaker if clipped long enough and hard enough. However, a more powerful amp driven to the same average power level (without clipping) would kill the speaker just as quickly.

My recollection is that 100 watts RMS translates to about 50 watts average power, so (assuming my recollection is in the ballpark) if a woofer is rated at 100 watts RMS it cannot be killed by a 40 watt amp driven into 100% clipping.

Clipping is especially nasty to tweeters because the crossover routes the higher clip-generated harmonics to the tweets... but that's another story for another day.

 

[B-string]

Tube amps have a transformer as the primary load to the output devices (tubes), the primary can be affected by the load placed on it's secondary. A "tap" (2,4 8 ohm) is needed for the primary to properly load the Tubes. SS are connected directly from the output devices to the load (speakers). This is why SS amp will fry if ran into a short and Tube amps can be damaged if no load is connected.
On the "square wave" business, that "flat topped" wave contains many harmonics that will still be reproduced as the power reserves needed to reproduce them drops the higher the frequency.

 

[B-string]

QED. Also .sig worthy. A double winner, ladies and gentlemen.

I'm honored! Thanks

 

[Alex1984]

It's heat that fries voice coils, not a specific waveform.

If the voice coil gets hot enough, something bad will happen (glue melts, metal deforms, voice coil former ignites, magic smoke escapes, atoms split, known universe collapses into a singularity, Chuck Norris loses a fight, whatever). A big enough megazap of power can fry a voice coil virtually intantaneously, or a steady application of more heat than it can dissipate over time will do the same thing.

A high power amp can zap the voice coil, or slow-cook it. A low powered amp's only hope to kill the speaker and get the rest of the night off is the slow-cook. Here's how that can happen:

The more deeply an amp is driven into clipping, the higher the *average* power it's putting to the voice coil is. So if an amp is powerful to put out a distorted waveform whose average power level exceeds the thermal capacity of the speaker, it can theoretically kill the speaker if clipped long enough and hard enough. However, a more powerful amp driven to the same average power level (without clipping) would kill the speaker just as quickly.

Clipping is especially nasty to tweeters because the crossover routes the higher clip-generated harmonics to the tweets... but that's another story for another day.

Thanks, that was very informative!

I've been led to believe since it's a magnetic structure, the driver is suppose to act more like an electromagnetic structure (differentially-driven by the rate of change, rather than linearly-driven). Guess that's where I've gone wrong.

Thanks for all the info!

 

[Alex1984]

Tube amps have a transformer as the primary load to the output devices (tubes), the primary can be affected by the load placed on it's secondary. A "tap" (2,4 8 ohm) is needed for the primary to properly load the Tubes. SS are connected directly from the output devices to the load (speakers). This is why SS amp will fry if ran into a short and Tube amps can be damaged if no load is connected.
On the "square wave" business, that "flat topped" wave contains many harmonics that will still be reproduced as the power reserves needed to reproduce them drops the higher the frequency.

Interesting, can this kind of design be applied to solid-state amps, or is it a characteristic or tube amps? It would be nice to have amps with switchable impedance so that it can provide the most amount of power at any impedance.

QSC working on anything? BTW, Bob, I think I've seen your posts at PSW and other audio forums, nice to finally get to converse with you!

 

[DukeLeJeune]

Thanks, that was very informative!

Thanks Alex.

Please don't tell anyone, but when I first came here a year and a half ago I believed that square waves over-stressed speakers somehow... and I'd been a speaker manufacturer for years! What I wrote in my post is stuff I learned here.

Duke

 

[JimmyM]

Interesting, can this kind of design be applied to solid-state amps, or is it a characteristic or tube amps? It would be nice to have amps with switchable impedance so that it can provide the most amount of power at any impedance.

if a solid state amp is made with an output transformer, then it can be applied. however, there are extremely few solid state amps being made that way. the warwick hellborg power amp is one of the rare few, and honestly, i don't know of any others.

however, trying to eke out every little tiny bit of power out of an amp is a losing game. first off, the difference with the wattage makes only a slight increase in available volume. second, most people who try to do that also try to get the smallest possible cabs they can find in a vain effort to make up for the smallness of the cab. but what happens is they end up blowing their cabs because they don't realize that it's the cabs that make the biggest volume difference. third, there is no third. fourth, even if you have all that volume available to you, most of us don't run anywhere near that much volume on a gig, lest we get canned.