Can't blow a speaker by under powering it.......

[two fingers]

Wait! No flames! I get it. I just can't explain it.

I was talking to a friend earlier and he was throwing the old conventional "wisdom" at me about blowing a speaker by under powering it. And I have seen posts on this forum dozens of times that say it isn't true. But I couldn't explain to him WHY it isn't true. Now I am only a few month into an electronics degree. I understand some terminology but not the most complex (and he is about the same). Help me explain this in the simplest terms you can come up with other than "It's true so shut up."

Please and thank you.

(builds fort to block many sharp objects being hurled in his direction currently)

 

[makohund]

Simplest... if it were true, every cab would blow as soon as you turned the amp off, and it saw "zero power". Or before you plugged it in, for that matter. Or sitting around before it was purchased. Or even as soon as it was built.

Not to mention every space between every note, even when you are playing it.

 

[Bassamatic]

Speakers are designed to handle a certain amount of power. Ergo - they cannot be damaged by being run at less than the rated power. However - - - -

This thinking probably comes from the days of under-powered stereo amps blowing out tweeters. The reason is that when an amp clips, the resulting square wave is composed entirely of higher harmonics, causing the entire output of the amp to be sent to the (usually cheap) tweeter, blowing it. tweeters are usually rated for a small fraction of the power of the woofer, so this was very common whenever anyone turned up the bass on a cheap stereo. I was managing a pawn shop back during the "disco days" and I must say that 90% of the speakers we saw had blown tweeters.

The fact is that more tweeters are blown by small amps than big amps.

This probably won't happen with any bass cabs because -

1. The piezo type tweeters impedance rises with frequency, so it is very hard to damage them
2. High end cabs with conventional tweeters have a fuse or circuit breaker for protection.

 

[JimmyM]

Amps can put out over twice their rated power in distorted power (usually called "peak power"). If you turn it up to the point where that distorted power is more than your cabs can take, such as a 250w RMS amp in a cab rated to take 400w, then you could theoretically be putting 500w into it on your peaks, which can kill the cab. But that's not underpowering...that's OVERpowering. Your amp can clip all day long as long as the speakers are built to handle that amount of power, otherwise distortion boxes and synths would blow cabs instantly.

 

[Mehve]

If you and your friend are at the point where you can visualize an AC wave, then do so. Then imagine that you're trying to output that wave from an amp that can't generate a high enough voltage peak (ie amp isn't strong enough). So the waveform gets clipped and has a flat top and bottom.

Now the important part-that "flat" part is actually a bunch of high frequency junk. And it all goes to the high frequency section of the cab, usually blowing the tweater first.

 

[punkjazzben]

The simplest way is to show your friend what happens when you turn the master volume down on the amp... nothing!

 

[arai]

If you have a 400 cab and a 50 watt head the cab will try to draw 400 watts out of the head and blow up

 

[punkjazzben]

If you have a 400 cab and a 50 watt head the cab will try to draw 400 watts out of the head and blow up

You're joking, right? 400 watts is what the cab can handle, not what it needs.

 

[f.c.geil]

The problem lies in confusing specs on paper with reality. If your spec sheet says that an amp produces 500 watts RMS, and the cab can handle 600 watts, some people will contend that you are 'underpowering' the cab. The reality of it is that there are a couple of fallacies in this argument:

first, the cab will fart out long before reaching the rated power handling. Continuous farting out can tear cones. Thus, your 'underpower' amp blew your cab. Of course, too much amp (601 watts or more, in this case) would do the same.
second, when distorting, your amp will put out as much as twice its rated power. Thus, you are putting 1,000 watts into your 600 watt cab. So, even though paper says you are 'underpowering' the cab, the reality is that you are overpowering it.

 

[Downunderwonder]

The problem lies in confusing specs on paper with reality. If your spec sheet says that an amp produces 500 watts RMS, and the cab can handle 600 watts, some people will contend that you are 'underpowering' the cab. The reality of it is that there are a couple of fallacies in this argument:

first, the cab will fart out long before reaching the rated power handling. Continuous farting out can tear cones. Thus, your 'underpower' amp blew your cab. Of course, too much amp (601 watts or more, in this case) would do the same.
second, when distorting, your amp will put out as much as twice its rated power. Thus, you are putting 1,000 watts into your 600 watt cab. So, even though paper says you are 'underpowering' the cab, the reality is that you are overpowering it.

That is the best description of the realities of "underpowering" I ever read.

Getting a bigger amp solves nothing. Get more speakers and "underpower" them some more and get the volume you wanted.

 

[1958Bassman]

Speakers are designed to handle a certain amount of power. Ergo - they cannot be damaged by being run at less than the rated power. However - - - -

This thinking probably comes from the days of under-powered stereo amps blowing out tweeters. The reason is that when an amp clips, the resulting square wave is composed entirely of higher harmonics, causing the entire output of the amp to be sent to the (usually cheap) tweeter, blowing it. tweeters are usually rated for a small fraction of the power of the woofer, so this was very common whenever anyone turned up the bass on a cheap stereo. I was managing a pawn shop back during the "disco days" and I must say that 90% of the speakers we saw had blown tweeters.

The fact is that more tweeters are blown by small amps than big amps.

This probably won't happen with any bass cabs because -

1. The piezo type tweeters impedance rises with frequency, so it is very hard to damage them
2. High end cabs with conventional tweeters have a fuse or circuit breaker for protection.

The entire output of the amp isn't sent to the tweeter(s). It's sent to any driver(s) that don't have an inductor ahead of them which, in the days when you were at the pawn shop, were very common- I saw the same thing at the stereo store where I worked. The output still goes to those drivers but their impedance rises toward the high frequencies and this helps them survive the harmonics.

Remember seeing speakers with a dome light from a car? That helps, too- the filament gets hot and its resistance increases, keeping excessive voltage/current from reaching the tweeter(s).

 

[1958Bassman]

Wait! No flames! I get it. I just can't explain it.

I was talking to a friend earlier and he was throwing the old conventional "wisdom" at me about blowing a speaker by under powering it. And I have seen posts on this forum dozens of times that say it isn't true. But I couldn't explain to him WHY it isn't true. Now I am only a few month into an electronics degree. I understand some terminology but not the most complex (and he is about the same). Help me explain this in the simplest terms you can come up with other than "It's true so shut up."

Please and thank you.

(builds fort to block many sharp objects being hurled in his direction currently)

There are very few reasons for a speaker being damaged, other than someone intentionally or accidentally doing physical damage (poking holes, ripping out the cone, dropping it, etc). Regardless of the actual cause, over-excursion is one- caused by lack of damping by the cabinet or extremely low frequencies driven past the driver's limits at any power level that makes it flap around like a fish on land. The other is heat. Heat damages the voice coil and can melt the coating on the wire, the glue on the voice coil former, the former itself and if it gets hot enough, the wire can stretch from the force of the magnetic field. In extreme cases, the wire can break from stretching or fuse because the current flowing through it is too much.

High frequency oscillation can cause a voice coil to die, too. The speaker can't reproduce the frequencies audibly, but that doesn't mean they're not going through the coil. The tell-tale sign is dark helical stripes on the coil, seen when the speaker is disassembled. Once the thermal limits of the speaker are reached, it fails and it doesn't matter what the power level is but, assuming undistorted signal amplitude without exceeding normal frequency limits/range or oscillations, low power will not damage a speaker.

It's not low power that kills speakers, it's using a rig that can't output enough power to reach the SPL the player needs, causing them to crank the volume, gain & tone controls to WOT, creating massive distortion and loss of amplifier damping or DC at the output terminals/jack(s).

If you want to mess with the guy who told you about the damage caused by low power, yell "DON'T TOUCH THAT- YOU'LL KILL US ALL!!!!!!!!!!!!!!!!!" next time he starts to turn the volume down on a stereo, radio or his amp.

 

[ChuckTrucks]

WIth his logic all speakers and amps should come prewired at a RMS power and when you turn them on you either get that volume or you have to turn it back off.

 

[Flux Jetson]

If you have a 400 cab and a 50 watt head the cab will try to draw 400 watts out of the head and blow up

No. This is not even close to correct. You're confusing power handling ability of the speakers with resistive load. "Watt rating" does not describe what the cab will draw, it describes what the cab will handle.

What you're saying is kinda like saying that a fat guy will get fatter if he doesn't eat enough.

 

[JTE]

Here's how "underpowering" was explained by Peavey when I attended their dealer training seminar in the mid '80s. When you drive the amp into clipping it clips the wave so that there's a squared off portion of the wave. That was thought to cause the voice coil to stay in one position while the current was going through it. Because the voice coil wasn't moving the idea was that there wasn't sufficient cooling going on, and the VC would eventually fail.

So, the spurious arguments about no volume, turning down the master volume, etc. are just about as silly as the original premise. No need to be derisive about this, just look at what's really happening.

BTW, turning down the master volume doesn't result in less power at the speaker outputs, just reduces the gain going to the power amp. Turning down the master volume on a Twin Reverb doesn't change its output level from 100 WRMS at all so that has NOTHING to do with "underpowering".

John

John

 

[CL400Peavey]

Here's how "underpowering" was explained by Peavey when I attended their dealer training seminar in the mid '80s. When you drive the amp into clipping it clips the wave so that there's a squared off portion of the wave. That was thought to cause the voice coil to stay in one position while the current was going through it. Because the voice coil wasn't moving the idea was that there wasn't sufficient cooling going on, and the VC would eventually fail.

So, the spurious arguments about no volume, turning down the master volume, etc. are just about as silly as the original premise. No need to be derisive about this, just look at what's really happening.

BTW, turning down the master volume doesn't result in less power at the speaker outputs, just reduces the gain going to the power amp. Turning down the master volume on a Twin Reverb doesn't change its output level from 100 WRMS at all so that has NOTHING to do with "underpowering".

John

John

so much of this is erroneous.

 

[will33]

In simple terms, a voice coil is simply a coil of wire, usually copper or aluminum. Watts not only tell you power but heat. The wire can only stand soo much heat before it melts or shorts out. You can apply less heat (power) to it all day long and it won't hurt it, thus, you can't " underpower". If you overpower, apply too much heat, you can and will blow it.

Kinda like butter or candle wax. You can freeze the stuff and it stays intact. Get it to a certain temperature ( heat or power in the speakers case) and it melts.

 

[JTE]

so much of this is erroneous.

What? The explanation given by Peavey (which is erroneous), or the commentary about how a master volume works on an amp?

John

 

[CL400Peavey]

What? The explanation given by Peavey (which is erroneous), or the commentary about how a master volume works on an amp?

John

Both,

Clipped signals or "square waves" dont cause the speaker to stop moving or damage speakers, if they did than every guitar player in the world would hit any sort of distortion or overdrive and his cabs would go silent and then fail.

Moving the volume know does change the power presented to the speakers via changing the limits of the voltage sent to them. if the same power (current) was presented to them all of the time they would make no sound and then burn up.

 

[mech]

Both,

Clipped signals or "square waves" dont cause the speaker to stop moving or damage speakers, if they did than every guitar player in the world would hit any sort of distortion or overdrive and his cabs would go silent and then fail.

Moving the volume know does change the power presented to the speakers via changing the limits of the voltage sent to them. if the same power (current) was presented to them all of the time they would make no sound and then burn up.

Are you saying a DC voltage will not make a speaker move and stay in that position? If so hook up a 12 VDC car battery to a speaker, leave it for a while and see if the coil doesn't get hot or burn open, depending on the ratings of the speaker.

mech