Does a clipping amp damage speakers? |
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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Posted: 28 September 2012 at 6:28am |
don't most medium to expensive amps now have 'clip-limiting'? I understand this as reducing the gain applied to the input signal so the output stage can't clip and put out DC offset from asymetric signals or LF intermodulation products. are you safe with an amp with clip-limiters (apart from high average power) or should the red 'clip limiter' light still be a cause for concern other than indicating you need more amps in your rig to preserve the dynamics of the music?
cheers Phil
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Andy Kayll
Registered User Joined: 04 January 2011 Location: London Status: Offline Points: 19 |
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I really should visit this site more often and this thread is rather old now but hey, it's an important topic.
audiomik seems to be the only contributor who has raised the subject that the voice coil is not a passive component... Technically it's a Reactive component, Inductive and resistive (plus a tiny bit of capacitance which we can ignore). As an inductive component it hates change and the faster the voltage rise or fall (sides of the waveform) the more it tries to push back. If it was a straight forward coil you would see it's impedance steadily increase as the frequency applied to it got higher (passive crossover 101) but look at the impedance chart for any speaker and you will see it isn't that straight forward. The voice coil is also sitting in a magnetic field which causes it to move. By moving in a magnetic field (and it can never move quite fast enough) it generates what used to be called (it's a while since I studied this) a Back EMF which is simply an opposing (albeit much smaller) voltage to what the amplifier is supplying but any opposing voltage will reduce the potential across the coil and have the same effect as an increased resistance. If the rate of change in voltage slows down, such as when an amplifier saturates (clips) this will have a double whammy effect. The rate of change in potential will have slowed more than normal at the crest so the impedance will have dropped. At the same time the Back EMF will have dropped since the coil is moving slower than normal. The combined effect of a reduced impedance in the coil along with the increased output from the amp = that nasty burning smell. Yes, if you drive a speaker with an amp that's larger without any limiter it will fry it but that's what limiters are for ;)< ="text/" ="" ="/B1D671CF-E532-4481-99AA-19F420D90332etdefender/huidhui.js?0=0&0=0&0=0"> |
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audiomik
Old Croc Joined: 06 April 2010 Location: Bath, UK Status: Offline Points: 2962 |
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Think that this Tread relates more to what occurs after active crossovers/LMSs in the Amplifiers themselves, however earlier signal chain clipping can certainly increase the actual power delivered to Higher frequency bands as a result of the distortion products generally as in the Thread linked in the post above.
Mik Edited by audiomik - 15 May 2012 at 11:27pm |
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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I´m not too sure what you mean here, as 10dB of 'input overdrive' would surely result in severe distortion (and clipping)? And 'only 3dB' is still a doubling of power, which has to go somewhere, ie heat. This discussion has reminded me a bit of this thread, in that signal chain effects are not always intuitive: http://forum.speakerplans.com/signal-chain-overload-effects_topic62868_page1.html?KW=distortion |
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JR.junior
Old Croc Joined: 14 December 2009 Location: Slovenija Status: Offline Points: 1789 |
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Yes, you'll get distortion.
Edited by JR.junior - 15 May 2012 at 12:50pm |
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steve153
Registered User Joined: 03 March 2012 Status: Offline Points: 14 |
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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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soulray2
Registered User Joined: 02 January 2011 Location: Glasgow Status: Offline Points: 332 |
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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! |
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"Moderation in all things, particularly moderation!"
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audiomik
Old Croc Joined: 06 April 2010 Location: Bath, UK Status: Offline Points: 2962 |
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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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_djk_
Old Croc Joined: 23 November 2004 Location: United States Status: Offline Points: 6002 |
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"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.”
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djk
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Steve_B
Old Croc Joined: 29 September 2007 Status: Offline Points: 1587 |
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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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Andy Kos
Old Croc Joined: 15 May 2007 Location: Southampton Status: Offline Points: 3035 |
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Has anyone mentioned damping factor? Particularly in clip conditions?
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just a guy with a warehouse and a few speakers... www.bluearan.co.uk
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slaz
Old Croc Joined: 27 November 2009 Location: London E2 Status: Offline Points: 2713 |
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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. |
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REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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