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Does a clipping amp damage speakers?

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Liteworks View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Liteworks Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2012 at 7:50pm
Originally posted by Earplug Earplug wrote:

Originally posted by GEB GEB wrote:

Just a few points from QSC, although I'm sure some know better! Wink

Clipping is bad for loudspeakers because it really heats up the voice coils.
Myth.


I really don´t think this one can be dismissed so easily. Clipping = greater average power = more heat = greater stress on the glues used in the driver = less life for the driver. Keeping the VC as cool as possible through proper venting and/or heatsinks isn´t done for nothing.



The clipping it's self isn't the cause of loudspeaker failure, it's the symptom of the problem, i.e. 'not enough rig for the gig' (as the yanks say on PSW), your hitting the end stop on the amp (and speakers if powered properly) and most likely going well pasted them.

Lost of people, especially nearer the bottom end of the game, tend to have mediocre amps (and speakers) and push them to hard to get anywhere near enough spl (also an amp driven hard into clipping sounds louder which add's to the issue), while a system powered with an amp that is rate at the same RMS figure as the drivers sounds like a good idea, once it's driven hard it's then producing far more output (with far more distortion) and the drivers get burnt.

The question asked is probably slightly wrong (or being answered slightly wrong), as clipping it's self does not damage speakers, but it usually indicates there is a problem that will result in a loudspeaker failure.  Certainly from the pov of operating a PA system, different ball game if your talking about guitar amplifiers for instance (as Bob mentions in the QSC forum I posted a link to).

matt




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Post Options Post Options   Thanks (0) Thanks(0)   Quote GEB Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2012 at 8:20pm
Originally posted by duck1 duck1 wrote:

I would agree with the cause of failure being excessive average power.

At the end of the day, the voice coil is just a piece of wire which will burn out when it gets too hot.

I think what Bill Fitz' was suggesting is that square waves, like the sort a synthesizer is capable of producing, are made up of every harmonic- this is why a square wave bass tone still has a buzz or sharpness to the sound. But, this is not the same as an amplifier output stage in clip which would be dumping DC from the rails into the speaker, and therefore subjecting the voice coil to much greater average power.



LOL


The experts would say your talking crap dude and don't know your arse from your elbow! No DC in a clipped amplifier signal I'm afraid!
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Peter Papp [PKN] View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Peter Papp [PKN] Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2012 at 8:56pm
There are different type of clipping events from various reasons.
When the peak range of signal reaches or exceed the rail Voltages of the amplifier it is Voltage clipping.
When the output current exceeds the current limit of an amplifier it is Current clipping.
Any type of clipping means awful level of signal shape distortion so it means that the output is NOT the level amplified input (it would be the basic function of a power amplifier)...
Very few amps have the ability of proper Voltage and Current limiting which would prevent clipping and maintain the integrity of signal in most of the cases happening on the user side.
The event of clipping is bad in every technical aspects and need to avoid it however there are some guys who like this effect due to added extra sounds in the output :-)

The clipping seriously increase the THD, typically by several tens of %... sounds pretty bad.
The clipping strongly increases the AVERAGE Power level and heat dissipation across the voice coil
The clipping could create extra harmonics which located may outside (lower / higher or booth) of the actual speaker and this way may hurt the mechanical structures.
At the moment of clipping the amplifier completely looses control of speaker movements!

Most of the professional amplifiers are not DC coupled and even few Hertz Hi-pass filtering located somewhere in the signal chain so there is no DC in the clipped signal. However in case of heavy clipping the output signal could be just like a square wave with typically 2X higher average power levels than normal sine has.
Most of the speakers would not survive even driven by continuous full amplitude sine wave (at their rated power..) so you can imagine what the square does!



Edited by Peter Papp [PKN] - 14 May 2012 at 8:59pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2012 at 9:06pm
"an amplifier output stage in clip which would be dumping DC from the rails into the speaker, "

This description is incorrect, and is NOT what is causing the problem.

"Clipping = greater average power"

During the un-clipped portion of the program material.

The extra power from the added harmonics it trivial.

The difference between a sine wave and a full square wave (which a clipped audio signal is not) is only 3dB.

Clipping occurs largely on transients in the program material. On most well designed amplifiers most people cannot detect clipping by ear unless it is driven more than 10dB into clipping, or for more than 40mS of duration.

At 120 BPM the clipping might be for 40mS + 40mS, of for 80mS of every second. 92% of the time the amplifier will not be into clipping.

BUT

With 10dB of input overdrive, even if you have a peak limiter that keeps it from clipping, the increase in average power of 10dB during the un-clipped 92% portion of the program material will increase the long-term average power to the driver to the point where it may fail.

The at most 3dB increase of power for the short duration of the clipping is trivial compared to the  10dB increase in long-term average power during the un-clipped portion of the program material.

I will try to explain why certain amplifiers can cause mechanical damage to woofers when clipped when I have some time later on, it will take quite a bit and require the reader to understand a bit of amplifier circuits and design.

Off to work I must go.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2012 at 9:19pm
Originally posted by _djk_ _djk_ wrote:



The extra power from the added harmonics it trivial.



I'm no expert, but I would have thought the "corner" of a risng waveform sharply clipped would "resolve" to significant harmonics - which - in the case of a passive Xover system could chuck a fair bit of extra power into (e.g.) a compression driver.
REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Andy Kos Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2012 at 9:24pm
Has anyone mentioned damping factor? Particularly in clip conditions?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 15 May 2012 at 1:08am

I can't really add anything of a technical nature that has not already been covered. However, for a rig user point of view, I think it is bad to get into the mindset that everything will be fine as long as the amps don't clip. As Matt (Liteworks) said, the problem is  usually 'not enough rig for the gig' . If you are blowing drive units, you have reached the limit of the transducer making the noise. Using a bigger amp to go louder won't work.

Many years ago (1970s) we ran into a problem of blowing compression drivers. This was an active system. Initially we had considered the rig to be harsh sounding when pushed. An oscilloscope. showed that the bass amps were clipping. The distortion was masked to a large extent by the acoustic low-pass filter that was a folded horn. The compression driver amps still had plenty of headroom and continued to get louder, hence the harshness. The solution was to compress/limit the high frequency amps. This got rid of the harshness, but now the compression drivers were failing more often.

It has to be remembered that back then 20W power handling in a compression driver was a lot. The compressors were doing what they should and knocked back the peaks. The average power level went up far enough to fry the voice coil.

It might surprise some that signal clipping has been used as a form of protection.

From a paper published by Electro Voice entitled “An electronic loudspeaker enhancement and protection device”, they state that for preventing damage caused by over excursion, clipping the signal can be a good thing.

“In order to limit the diaphragm excursion to a safe level, it is necessary to prevent voltages that exceed the excursion-voltage limits  from reaching the speaker terminals. If this voltage limiting is accomplished using gain reduction, then the extremely fast attack time which is needed, and the requirement of absolute peak protection, can result in excessive overlimiting. This is a serious form of dynamic distortion of the program material. Another method of limiting the voltage at the speaker terminals is to clip the signal. This method is preferable because the signal is only affected during the offending transient, and the signal path gain is instantly restored. While clipping is not a subtle form of distortion, speaker diaphragm crashing is much worse.”

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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 15 May 2012 at 2:36am
"I'm no expert, "
 
Far, far from it.
 
"but I would have thought the "corner" of a risng waveform sharply clipped would "resolve" to significant harmonics - which - in the case of a passive Xover system could chuck a fair bit of extra power into (e.g.) a compression driver."
 
A sine wave with all its odd harmonics out to infinity is a square wave. A square wave only contains 3dB more energy than a sine wave. Heavy clipped program material does not look as bad as a square wave. A trivial amount of power increase.
 
At the risk of repeating myself:
 
"The at most 3dB increase of power for the short duration of the clipping is trivial compared to the  10dB increase in long-term average power during the un-clipped portion of the program material."

"Has anyone mentioned damping factor? Particularly in clip conditions? "
 
That is why you want to clip the input to the power amplifier.
 
"This method is preferable because the signal is only affected during the offending transient, and the signal path gain is instantly restored. While clipping is not a subtle form of distortion, speaker diaphragm crashing is much worse.”
djk
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 15 May 2012 at 12:13pm
think that you may be not be looking at the full picture here

When an asymmetric waveform, as very often occurs with a music program source, containing a combination of two different frequency components (or more) is run into clip; Inter-Modulation Distortion (IMD) occurs.

This amongst other artifacts will produce a product equal to (F1 - F2) plus a whole series of others which are the sums and differences of the two (or more) 'fundamental' frequencies present in the original signal plus other distortion products.

Say for example that your two frequencies are at 80Hz (F1) and 50Hz (F2), for simplicity, then (F1 - F2) = 30Hz which you have carefully filtered out prior to the signal being sent to the Amplifier so as to not exceed Xmax for your 'Speaker..... but is now reintroduced, additional to the original signal, as you have over-driven your Amplifier into a non-linear mode (clipping).
The same occurs with the method of using back to back diodes or equivalent circuitry to peak limit signals by clipping before your Amplifier input but after your High Pass filtering.
Shifting the values of the example frequencies also shows how HF Compression Drivers can be damaged by out of band frequencies after the LMS/Analog active crossover filtering.
FFT Analysis of the composite clipped signal will easily show this - see previous post.

Now with an Amplifier rated to give a maximum* output within the sine-wave power capability of the 'Speaker being driven then this might not be a problem, but if the Amplifier is of larger capability then expect problems.

There is plenty of information readily available on IMD and it's causes on the Net

Mik

Edit: add comment on frequency variation
* Maximum output is the power when the Amplifier is driven well into clip and is twice the sinewave rated output.


Edited by audiomik - 15 May 2012 at 11:19pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote soulray2 Quote  Post ReplyReply Direct Link To This Post Posted: 15 May 2012 at 12:17pm
Originally posted by GEB GEB wrote:

Seems the correct information from what I can gather from those who are not talking out their bottoms is that clipping does not cause damage to speakers, but a clipping amp 'may' deliver too much power into the speaker and cause it to fail, in which case it would happen on a more powerful amp regardless. If it were true guitar speakers would fail left, right and centre. There is not DC present in a clipped signal, people are confusing themselves because of the square tops of the signal, were as DC wouldn't be made up of + & - element components in the first place. And the coil doesn't stand still and effect cooling as no sound would come out of the speaker in the first place if it was still!

Is that the general jist of it?


I'm no expert, GEB, but this is my general/pragmatic understanding of this too!

As a rule of thumb, if you're using an amp which is more powerful than the rating of your speakers, (because you like the headroom or sound quality etc), then you best not drive it into clip, because it can then deliver more long term power than your speakers can handle!
If you're using a 50w amp on a 500w speaker, knock yourself out!Wink
"Moderation in all things, particularly moderation!"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve153 Quote  Post ReplyReply Direct Link To This Post Posted: 15 May 2012 at 12:29pm
Originally posted by soulray2 soulray2 wrote:

 
If you're using a 50w amp on a 500w speaker, knock yourself out!Wink

This thread has been so informative, cleared up so many areas of confusion for me in regards to the topic. However, how true is the above statement?

Is to protect the speaker cone (and the life of your amplifier) the only reason you don't send a clipped signal into a speaker. Does it a clipped signal affect the sound drastically in a negative way?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JR.junior Quote  Post ReplyReply Direct Link To This Post Posted: 15 May 2012 at 12:50pm
Yes, you'll get distortion.

Edited by JR.junior - 15 May 2012 at 12:50pm
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