Coil rub cause amp to blow?

[It happens 10+ year member]

I was curious if having coil rub or a off balanced/ non linear coil cause a amp to blow out? Thanks in advance

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[Doxquzme Premium Member]

Usually, it’s not the amp that gets burned; it’s an overdriven, clipping amp that burns the woofer. That said an amp that is being driven to clipping for long periods of time it can be ruined and conversely, the driver too. In my experience I have seen far more woofers or large diaphragm, low freq. drivers ruined than high freq. speakers like tweeters from under-powering. That’s because they have crossovers (usually utilizing 250v caps or better where the subs, not so much). In the case of under-powering, the driver is blown because the amplifier is driven to the point that it can no longer amplify the signal. The amp tries to generate the amplified version of the input waveform, but runs out of "headroom" before the full wave is generated. The result is a square wave. The sinusoidal version of the waveform is only partially generated and the result is a square wave with a "plateau" on the top. The "plateau" is pretty much a DC current at that point. DC in large enough amounts is what burns up speakers. The driver is only driven part of the way in or out, but it is held in a suspended position at the top of the square wave the amp is generating. The result is the speaker is in a near DC state and the constant voltage without any corresponding movement causes the windings of the voice coil to heat up.

Eventually the heat is too great for the windings and they burn up. In practice, the motion of the speaker also pulls in cooler air and forces out the heated air around the voice coil. With the speaker mostly in the motionless state, but with voltage being applied there is no cooling from the speaker moving in and out. In the case of too much power, the amplifier is sending more power than the voice coil windings can stand and they burn up, or...

In the case of woofers, the voice coil is bottomed-out against the magnet. ( could be the rubbing you're talking about) This causes a distortion in the shape of the voice coil. Once the voice coil is distorted in shape the windings rub against the sides of the gap (more likley the rubbing you're aling about). They either wear though or are so thin that power surge burns them out at the weak point caused by wear.

Honestly though, I would suppose that trying to make a blown woofer do its thing could cause overheating issues with the amp. If you have a blown amp, it’s likely the reason that you have a blown driver.

**** NOTE, there is no such thing as an “off balance” VC, if it’s rubbing, dinging or clacking, there is something wrong, mechanically.

 

[hispls 5,000+ posts]

With the speaker mostly in the motionless state,

Your speaker will pump the exact same number of times per second and to the same excursion with a square wave as a nice round looking one. Square wave just gives you 30ish % more current over time. The shape of the waveform isn't what burns up coils.

I was curious if having coil rub or a off balanced/ non linear coil cause a amp to blow out? Thanks in advance

It may be possible to short part of your coil and hurt your amp if you're rubbing too much of the shellac off of the windings and that's touching the top plate or something but typically coils burn open when they fail.

 

[Doxquzme Premium Member]

Your speaker will pump the exact same number of times per second and to the same excursion with a square wave as a nice round looking one. Square wave just gives you 30ish % more current over time. The shape of the waveform isn't what burns up coils.


It may be possible to short part of your coil and hurt your amp if you're rubbing too much of the shellac off of the windings and that's touching the top plate or something but typically coils burn open when they fail.

Your speaker will pump the exact same number of times per second and to the same excursion with a square wave as a nice round looking one. Square wave just gives you 30ish % more current over time. The shape of the waveform isn't what burns up coils.


It may be possible to short part of your coil and hurt your amp if you're rubbing too much of the shellac off of the windings and that's touching the top plate or something but typically coils burn open when they fail.

That's just splitting hairs. You’re elaborating on what was already said. The shape provides the conduit for DC to enter into the circuit. The shape is relative not responsible. What I said was not theory, it's a fact. It's what is being pumped that changes the heat value, the duration, etc, are all part of that equation, not the fact there is a force reaction up or down as would be present when any voltage is applied, unless shorted. In the end, it leads to driver failure. Running shorted drivers or speakers, can be or running an amplifier to clipping for long durations, will be detrimental to the amplifier and the speakers. To answer the OP, he’s got a driver with a mechanical fault; it could (will be) be problematic for the amp too. That is the answer to the question.

 

[Jimi77 5,000+ posts]

Wow. The "squared" waveform is called clipping, literally the top of the wave form is clipped off. Clipping can be good if the amp can handle it because it increases power and has the effect of increasing the apparent frequency the sub is reproducing, which usually means translates to greater efficiency from the driver. Just keep in mind you can't run the amp or sub clipped for long periods of time or you'll smoke one or both of them.

Rubbing VCs will usually lead to damaged equipment. And VC's can be off center, ie if you up or down fire a sub, it will sag in the suspension, which will affect the BL curves, etc.

 

[Doxquzme Premium Member]

Wow. The "squared" waveform is called clipping, literally the top of the wave form is clipped off. Clipping can be good if the amp can handle it because it increases power and has the effect of increasing the apparent frequency the sub is reproducing, which usually means translates to greater efficiency from the driver. Just keep in mind you can't run the amp or sub clipped for long periods of time or you'll smoke one or both of them.

Rubbing VCs will usually lead to damaged equipment. And VC's can be off center, ie if you up or down fire a sub, it will sag in the suspension, which will affect the BL curves, etc.

 

[Doxquzme Premium Member]

While I try to discourage the "Clipping is Okay" mantra (as for novices and even regulars it is a device better left to professionals), I agree with what you’ve stated.

 

[Jimi77 5,000+ posts]

While I try to discourage the "Clipping is Okay" mantra (as for novices and even regulars it is a device better left to professionals), I agree with what you’ve stated.

You don't need to be a professional. You just need to understand that music has much less rms output than the sine waves used to establish power handling in a sub. That's why you see so many systems with amps that are ~1.5-2x the subwoofer's rating, but set to no clipping and the sub survives. That suggests 3db of clipping is pretty safe. I wouldn't clip Brazilian amps, but solidly built Korean amps, I'd say you're good.

 

[Doxquzme Premium Member]

You don't need to be a professional. You just need to understand that music has much less rms output than the sine waves used to establish power handling in a sub. That's why you see so many systems with amps that are ~1.5-2x the subwoofer's rating, but set to no clipping and the sub survives. That suggests 3db of clipping is pretty safe. I wouldn't clip Brazilian amps, but solidly built Korean amps, I'd say you're good.

I get it but sometimes a little knowledge can be dangerous. Even with the Korean amps that I run (and I’m a fan) or the Focal a/b's that I run, I'm of the school that says double your amplifier output needed versus squeezing every last drop just to play there kind of thing. SPL versus SQL. Different folks, different strokes.

 

[Jimi77 5,000+ posts]

That's just splitting hairs. You’re elaborating on what was already said. The shape provides the conduit for DC to enter into the circuit. The shape is relative not responsible. What I said was not theory, it's a fact. It's what is being pumped that changes the heat value, the duration, etc, are all part of that equation, not the fact there is a force reaction up or down as would be present when any voltage is applied, unless shorted. In the end, it leads to driver failure. Running shorted drivers or speakers, can be or running an amplifier to clipping for long durations, will be detrimental to the amplifier and the speakers. To answer the OP, he’s got a driver with a mechanical fault; it could (will be) be problematic for the amp too. That is the answer to the question.

The shape doesn't create DC. The shape creates higher AC voltage and thus higher AC current and higher RMS power and more heat.

 

[Doxquzme Premium Member]

The shape doesn't create DC. The shape creates higher AC voltage and thus higher AC current and higher RMS power and more heat.

Didn't say it creates it.

The relationship between clipping level and DC voltage is, In summary, the clipping level is directly related to the DC voltage in a circuit, as it determines the maximum amplitude a signal can have before it gets distorted. Clipping circuits cut-out (chop) part of the input. Clipping circuits always add a DC voltage to the output. AND, yes, clipping circuits may be used to add a DC bias to the input. Clipping circuits can turn sinusoidal waves into square or triangular waves. All this is correct but in the end. The answer to the OP is:

Your woofer is broken or damaged and you should not use it on any amplifier or it will most likely result in something getting fried.

 

[It happens 10+ year member]

Could that happen in the first time ever using the amp though? While hooked up to the rubbing coil?

 

[Doxquzme Premium Member]

Could that happen in the first time ever using the amp though? While hooked up to the rubbing coil?

Depending on what is causing the coil issue to begin with, yes, definitely.

 

[It happens 10+ year member]

A shifted motor started the coil rub . So the coil was not centered to the yoke , I just loosened the motor and re centerd it and it took care of the rub

 

[spokey9]

In my experience I have seen far more woofers or large diaphragm, low freq. drivers ruined than high freq. speakers like tweeters from under-powering. That’s because they have crossovers (usually utilizing 250v caps or better where the subs, not so much). In the case of under-powering, the driver is blown because the amplifier is driven to the point that it can no longer amplify the signal.

That's user error you're describing...you can run a 100w amp to drive a 1k rms sub without damaging anything...just set your gain properly and you're golden...granted the sub will not get loud but you won't hurt the driver under powering it...