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Author Topic: Weekend wrriour power question  (Read 21468 times)

TJ (Tom) Cornish

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Re: Weekend wrriour power question
« Reply #60 on: January 19, 2013, 07:08:40 AM »

Tim (and everyone else) thank you for all the information.

I will just say the point i was trying to make was the clipping provides more heat in a quicker time frame then what the drivers are designed to take...
Hi Ben.  This is actually still mostly incorrect.  If it were true, every time a keyboard player played a square wave - a common synth building block - speakers would die.  The shape of the waveform is not primarily what causes driver death, it's the: 1. heating power in the waveform, or 2. the peak voltage of the waveform relative to the driver's capabilities.

1. - If I have a driver that can take 1000 watts average power and take a 500 watt amp and clip the snot out of it, which produces up to 2X the original power, I'm still at my 1000 watts, and my driver will be able to handle this for a long time, even though the signal is roughly a square wave.  Conversely, if I have a 250 watt driver and a 1000 watt amp, I may very well toast my driver long before the amp gets to clipping - with possibly as much as almost 6dB of amp headroom left. 

2. - If I can send a voltage spike to the driver sufficient to bang the cone or diaphragm against it's structural parts, it may die of mechanical impact even if there hasn't been enough heat to cause damage that way.

The big fallacy here is that people think if they buy a bigger amp they will save their speakers.  I wager this has almost never worked - the same morons people that run their system into clipping - whatever the system size - will happily continue to do so with an even larger amp, which will cause speaker death even more quickly.

Back on the shape of the waveform - people often get confused thinking that a square wave rises and falls so quickly that the driver "slams" back and forth.  The error in thinking here is that the driver movement follows what the waveform looks like.  The waveform shape is actually the graph of the electromotive force that causes the driver to move, not the driver motion - a quick transition from say -10v to 10v means the force causing the driver to move inward has stopped, and now a 10v force causing the driver to move out has begun.  The driver takes - at least relative to the rise time of a square wave - quite a long time to actually move from whatever minus position it was in to whatever plus position it gets to until the input signal changes, due to the mass of the driver, the air loading, etc.


For many longer (and sometimes more heated) discussions, search for the term "under powering".

Here's also a good article on the subject:
http://www.bennettprescott.com/downloads/LoudspeakerFundamentals.pdf
« Last Edit: January 19, 2013, 07:12:21 AM by TJ (Tom) Cornish »
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Greg_Cameron

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Re: Weekend wrriour power question
« Reply #61 on: January 19, 2013, 11:55:19 AM »

Back on the shape of the waveform - people often get confused thinking that a square wave rises and falls so quickly that the driver "slams" back and forth.  The error in thinking here is that the driver movement follows what the waveform looks like.  The waveform shape is actually the graph of the electromotive force that causes the driver to move, not the driver motion - a quick transition from say -10v to 10v means the force causing the driver to move inward has stopped, and now a 10v force causing the driver to move out has begun.  The driver takes - at least relative to the rise time of a square wave - quite a long time to actually move from whatever minus position it was in to whatever plus position it gets to until the input signal changes, due to the mass of the driver, the air loading, etc.

IIRC, someone pointed out that aside from the additional heating is that the clipped output of the amp causes greater excursion of a driver. This is because that additional power also means more electromotive force is applied compared to the same amp at maximum unclipped output. More power = more work done by the driver.
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Patrick Tracy

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Re: Weekend wrriour power question
« Reply #62 on: January 19, 2013, 12:44:33 PM »

IIRC, someone pointed out that aside from the additional heating is that the clipped output of the amp causes greater excursion of a driver.

If you restore the clipped peaks by using a bigger amp you'll get even more excursion at the same overall gain, not less.

This is because that additional power also means more electromotive force is applied compared to the same amp at maximum unclipped output. More power = more work done by the driver.

The question isn't if more power is more likely to burn speakers than less power. That's clearly true. The question is if the same power is more likely to burn speakers if it's clipped than if it is not clipped. It isn't.

Greg_Cameron

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Re: Weekend wrriour power question
« Reply #63 on: January 19, 2013, 01:03:13 PM »

If you restore the clipped peaks by using a bigger amp you'll get even more excursion at the same overall gain, not less.

Agreed. More voltage means more sourced current which means more power = more work done. The point I was making is that extra heat is not the only potential issue with clipping. You can also bottom out drivers in some cases too.

The question isn't if more power is more likely to burn speakers than less power. That's clearly true. The question is if the same power is more likely to burn speakers if it's clipped than if it is not clipped. It isn't.

Agreed.
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Tim McCulloch

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Re: Weekend wrriour power question
« Reply #64 on: January 19, 2013, 01:33:59 PM »

Agreed. More voltage means more sourced current which means more power = more work done. The point I was making is that extra heat is not the only potential issue with clipping. You can also bottom out drivers in some cases too.

Agreed.

And the reality is that neither condition is exclusive to clipping, simply that weekend warriors with too-small amps, bridged (without compensation for the 6dB increase in gain) and driving them hard, will heat up coils and exceed XMAX just like using a bigger amp, driving the speakers to the same SPL.

Too much heat, too great the motion.... and the speaker will eventually fail.

In general, killing speakers on a routine basis is a certain sign of Not Enough Rig for the Gig as well as questionable operating practices.
« Last Edit: January 19, 2013, 01:36:29 PM by Tim McCulloch »
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Re: Weekend wrriour power question
« Reply #64 on: January 19, 2013, 01:33:59 PM »


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