Why is it better to overpower than to underpower a speaker?

[beerthebear]

Just a question. I was told by countless people, that overpowering a speaker is much better than underpowering it. Anybody know exactly why that is? If anybody has the answer can you be as descriptive as possible? I just would like to learn a little more theory about speakers and wattage, etc.. Thanks!

 

[theLimeyBrit]

Overpowering = louder than underpowering.
The louder = the better.
Ergo, overpowering > underpowering.

 

[RWP]

There are several raging debate threads about this if you search. My opinion is; it's better to over power for this reason. If you under power you run the risk of driving your amp into clipping. Clipping is when the output voltage becomes limited by the power supply voltage causing a square wave. The voltage can not go past the limit of the supply voltage but the current will and that is what can cause damage. Crown suggests 1.5 to 2X the RMS amplifier power to the RMS speaker rating to provide ample headroom. YMMV IMHO

 

[Rattman]

"underpowering"? That term does not compute Will Robinson!

Could you be more specific? By any chance do you mean perhaps a 'mismatch'? It almost sounds like that the question would imply potential damage to a driver if it's played at low-gain levels? If so then I've been extremely fortunate all these years.

In the distant past, I blew two 15" JBL's, but the pre amp was apparently saturated.. so it was completely my fault that the voice coils became too hot and ultimately failed.

 

[beerthebear]

"underpowering"? That term does not compute Will Robinson!

By underpowering I mean say you have a sub that is rated at 500 RMS, and you hook up at amp 75 RMS and try to turn the volume really loud. I was told this is more dangerous than hooking up a 700 RMS amp to the 500 RMS sub. Just wondering what the deal is.

 

[metron]

In either case the speaker can fail due to a clipping amp putting out too much power or an amp thats not clipping but putting out too much power. In both cases what the speaker sees is the same - excessive current. Your voice coil will burn just the same. Some people ignorantly believe that too little power is a greater concern but thats just not the case.

 

[Rattman]

... oh yeah.. Yes, I do see what you are driving at, and I apologize for the syntax differances on my part.

I would have to say your instincts are correct: what you described is something you need to avoid if you value your drivers. The 2nd senerio matching the 700W head to the 500W cab would be much better.. IF you if keep in mind not to drive that rhetorical '500W cab' very hard. You would probably know.. there are some sonic indicators you are pushing it beyond the rated wattage capacity.

 

[WalterBush]

Clipping waveforms are a problem, but if you're hard clipping (complete square-wave) a 75 watt amp powering a 400 watt speaker, the speaker will still handle the power without breaking a sweat.

Dumping 800 watts of clean power into a 400 watt speaker will blow it, however, and no two ways about it. Obviously, if you own an 800 watt amp and don't turn it up all the way, you're not developing 800 watts, and may not blow the speaker.

After blowing way too many speakers to count, I always connect my amps to speakers that are rated much higher than the amp can put out. It's been a long time since I've blown a speaker, although I've had two die of old age (20+ years in extreme weather conditions)

Bear in mind that a square waveform can be achieved with the preamp, and the power amp will gladly pass it along without a hitch, and if your speakers aren't rated much, much higher than the power amp, they'll blow. I had a friend who couldn't understand why his distortion pedal seemed to cause amps and speakers to blow until I explained it to him.

 

[beerthebear]

Clipping waveforms are a problem, but if you're hard clipping (complete square-wave) a 75 watt amp powering a 400 watt speaker, the speaker will still handle the power without breaking a sweat.

Dumping 800 watts of clean power into a 400 watt speaker will blow it, however, and no two ways about it. Obviously, if you own an 800 watt amp and don't turn it up all the way, you're not developing 800 watts, and may not blow the speaker.

After blowing way too many speakers to count, I always connect my amps to speakers that are rated much higher than the amp can put out. It's been a long time since I've blown a speaker, although I've had two die of old age (20+ years in extreme weather conditions)

Bear in mind that a square waveform can be achieved with the preamp, and the power amp will gladly pass it along without a hitch, and if your speakers aren't rated much, much higher than the power amp, they'll blow. I had a friend who couldn't understand why his distortion pedal seemed to cause amps and speakers to blow until I explained it to him.

Okay just to learn a little electrical theory here. I understand that speakers get a AC voltage and current from a power source (ex. Head). This of course would be just a simple sine wave. I keep hearing about "clipping" and the ac wave turning into a square wave. So just a few questions:

1) Is this square wave act as a DC current? Hench DC voltage is bad for speakers.
2) What actually is clipping? From what I understand its providing too much current to a driver.
3) How does this AC sine wave turn into a square wave? and how?

I know these are petty questions, but I honestly would like to know why. I guess I like to ask a lot of questions

 

[Richard Lindsey]

Okay just to learn a little electrical theory here. I understand that speakers get a AC voltage and current from a power source (ex. Head). This of course would be just a simple sine wave. I keep hearing about "clipping" and the ac wave turning into a square wave. So just a few questions:

1) Is this square wave act as a DC current? Hench DC voltage is bad for speakers.
2) What actually is clipping? From what I understand its providing too much current to a driver.
3) How does this AC sine wave turn into a square wave? and how?

I know these are petty questions, but I honestly would like to know why. I guess I like to ask a lot of questions

Don't take this as a brushoff, but there is a LOT of material on this stuff in this forum if you search. (I know this because I've been a part of a number of the discussions.) Try that first, and see if it helps.

EDIT: I forgot that we were in the Miscellaneous forum (damn middle age!). What I should have said was that there is a lot of info in the Amps forum on this stuff if you search.

 

[Phalex]

1) Is this square wave act as a DC current? Hench DC voltage is bad for speakers.

You are on the right track. A square wave can be defined as "pulsed DC".


2) What actually is clipping? From what I understand its providing too much current to a driver

Clipping is asking too much of the amplifier. You have a high and a low as defined by the middle of the sine wave. If you have an amp capable of 100 watts and you overdrive it, it will reach it's 100watt limit and flatten the sine for the period of time it takes for the signal to drop back below it's 100 watt limit.

.
3) How does this AC sine wave turn into a square wave? and how?

Overmodulation of the input signal.

It's been about 20 years since I actually took this sort of thing in school, but I think my answers should prove to be fairly accurate.

 

[morf]

Its always been my understanding that you could much more easily blow a speaker than an amp, and it will cost alot more to repair as well.

My 2 cents...

 

[Sundogue]

Why is it better to overpower than to underpower a speaker?

Because it gives you headroom. Basically, as long as your amp is relatively close to the rating of your cab, or even rated as much as two time higher than your cab, AND you don't push your amp too hard (in either case), you should be fine.

All the components need to work together to get you what you want. If you want higher volume and want to keep your sound clean, simply buy speaker cabs that have a higher efficiency rating. Look for cabs with a higher SPL. The higher the SPL, the less watts your amp needs to be at to drive that cab with a clean signal.

I think cab efficiency is one of the most overlooked things when trying to piece together a rig, and results in more people driving their amps and cabs into oblivion when trying to get volume out of them.

Seems to me, too many people are hung up on watts. I think matching your amp with your cab's efficiency is more important than just how many watts your amp and cab are rated for.

 

[Richard Lindsey]

Why is it better to overpower than to underpower a speaker?

Because it gives you headroom.

That's not really so. The ratio between amp power and cab handling has nothing directly to do with headroom. What determines headroom is how much power you have in relation to how much power you need to do the job you're trying to do; the latter is not determined by your cab's power handling. (You're right, though, to say that cab efficiency, or rather sensitivity, is important, because that affects how you have to use your amp to get a desired volume and tone.)

As an example, for a gig that could be done with a 300 W amp, you have more headroom with a 600 W amp into a 1200 W cab of a given sensitivity and frequency response than you do with a 400 W amp into a 200 W cab of the same sensitivity and frequency response. Headroom is really all about how high you have to turn up the amp, not about whether or not you have more power than your cab is rated to handle.

 

[Sundogue]

That's not really so. The ratio between amp power and cab handling has nothing directly to do with headroom. What determines headroom is how much power you have in relation to how much power you need to do the job you're trying to do; the latter is not determined by your cab's power handling. (You're right, though, to say that cab efficiency, or rather sensitivity, is important, because that affects how you have to use your amp to get a desired volume and tone.)

As an example, for a gig that could be done with a 300 W amp, you have more headroom with a 600 W amp into a 1200 W cab of a given sensitivity and frequency response than you do with a 400 W amp into a 200 W cab of the same sensitivity and frequency response. Headroom is really all about how high you have to turn up the amp, not about whether or not you have more power than your cab is rated to handle.

You are correct. I was trying to simplify it.

Essentially you just want to have more watts available than what you need so it runs clean, even at higher volume (which may very well even be an amp rated at less watts than what the cab is rated for).

I do think that efficiency is one of the last things many think of when trying to assemble a rig (if they think about it at all). Too many look at watts as the be all and end all, and then still can't figure out why they can't hear themselves, or why it's so distorted when they play loud.

 

[Richard Lindsey]

Essentially you just want to have more watts available than what you need so it runs clean, even at higher volume (which may very well even be an amp rated at less watts than what the cab is rated for).

Absolutely! And sensitivity can affect that, as you say. An amp that's just barely enough for a given situation with my Acme B-2 might be easily more than enough with, I dunno, an Epifani or something. And the difference would be due to the increased cab sensitivity, not any difference in cab power handling per se.

 

[Sundogue]

Absolutely! And sensitivity can affect that, as you say. An amp that's just barely enough for a given situation with my Acme B-2 might be easily more than enough with, I dunno, an Epifani or something. And the difference would be due to the increased cab sensitivity, not any difference in cab power handling per se.

I throw the terms efficiency and sensitivity around in place of each other a lot.

Efficiency is a product of sensitivity and power handling, isn't it?

 

[Richard Lindsey]

The actual number that people use for speakers is considered a measure of sensitivity (e.g., XY dB @ 1 W @ 1 m).

Efficiency is sometimes used as a general nonspecific term for speakers that seem loud for a given amount of power input. We cpmmonly use the term to mean basically a cab that can get loud without needing a whole lot of power pumped into it.

IIRC, when used strictly, speaker efficiency refers to the ratio between actual acoustic power produced and electrical power input, and is commonly expressed as a percentage. No speaker is really all that efficient in the strict sense (we're talking single-digit percentages), because the vast majority of the power is not converted to acoustic output.

I think the product of sensitivity and power handling would be maximum acoustic output.

 

[Sundogue]

...maximum acoustic output.

Loosely translated...

How loud can I go without going broke?

 

[jesso]

Just another question here....
What if I have a PA speaker that is rated at 600watts RMS (at 4 ohms), but my power amp is only rated at 500watts (at 4 ohms)?
Is this asking for trouble? It seems like the power ratings are pretty close.... and I never run my amps into the red (or only very slightly if even at all) Shouldn't I be safe enough?