Does a clipping amp damage speakers?
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Topic: Does a clipping amp damage speakers?
Posted By: GEB
Subject: Does a clipping amp damage speakers?
Date Posted: 13 May 2012 at 8:17pm
| As per the title really, just wanted the 'pro's' opinions really? |
Replies:
Posted By: AJordan
Date Posted: 13 May 2012 at 8:23pm
| Cant claim to be a pro but yes seems to be the general opinion. The occasional clip probably not but sustained clipping yes. |
Posted By: Mircea Bartic
Date Posted: 13 May 2012 at 8:27pm
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every time
------------- general manager & head designer at nexus-acoustics research http://www.facebook.com/nexus.acoustics.research" rel="nofollow - http://www.facebook.com/nexus.acoustics.research Ex Nexus_3 |
Posted By: cyte
Date Posted: 13 May 2012 at 8:33pm
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Yes. Clipping introduces a DC element to the signal (flat peaks and troughs). DC kills drivers because when a current is flowing through the voice coil, it relies on the movement of the coil and air around it to cool it. With DC, there is no movement, and therefore no cooling so the temperature just increases until the coil burns up and shorts out. |
Posted By: AJordan
Date Posted: 13 May 2012 at 8:40pm
| I dont think thats true. There is no dc. even thought the clipped peaks of the waveform might look like dc. I think its just the much greater energy content of a clipped signal that heats the coils. |
Posted By: GEB
Date Posted: 13 May 2012 at 8:44pm
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So this from Bill Fitzmaurice is wrong then? Confused! Amplifier clipping, and it's respective causes and effects, is perhaps one of the most misunderstood concepts amongst audio circles. There is a whirlwind of myths surrounding this topic that seems to exceed all other topics I have come across. Now is your chance to learn the truth about clipping. How Do Speakers Become Damaged There are only two ways that a speaker can be damaged, both of which occur from too much input power. 1. Mechanically 2. Thermally Every speaker has an excursion limit (often measured in mm), or how far the speaker can move forward or rearward before damage occurs. This is the mechanical limit of the speaker. This limit remains the same regardless of the use of the speaker, but the power required to reach this limit changes dependent on the enclosure. If you exceed this limit, the speaker will suffer mechanical damage, whether it's ripping your spider, bottoming out on the back plate, or any other mechanical damage. The second type, thermal damage, occurs when you exceed the thermal power handling limits of the voice coil itself. Voice coils are simple pieces of metal that will melt if too much power is applied. This limit is pretty much constant, ie. if a voice coil will be damaged at 1 kw, it will be damaged at 1kw regardless. There are two final myths to cover here. Despite the tireless efforts of some, there are still many people that believe that underpowering a speaker will damage it or that clipping will damage a speaker. Please remember that these last two thoughts are entirely UNTRUE! And now we will find out why. Where Does This Power Come From? Let's first understand the power potential of an amplifier when clipping. The power created is largely determined by the rail voltages. Let's compare two amps, each one connected to a 4 ohm speaker rated at 75 watts rms. Amp 1: 50 watt amp 50 Watt amp means this amp can cleanly deliver a sinewave of 50watts into a 4 ohm load. This means (Vrms)^2/4 = 50W Vrms = 14.14V Vpeak = Vrms*(1.414) Vpeak = 19.99V The rail voltages of this amp must be a bit higher, to prevent output stage distortion at this power level. In this case, the Rail voltage would have to be +/- 20 Volts. Amp 2: 75 watt amp (Vrms)^2/4 = 75W Vrms = 17.32V Vpeak = Vrms*(1.414) Vpeak = 24.49V In the example, the 75 watt amp is delivering 75 watts as it is not distorting at all. The 50 watt amp is in hard clipping, as and such, is delivering a fair bit more power. P = Vrms^2/R = (19.99V)^2/4 ohm = 100 watts. It is quite obvious that there is potential for an amplifier that is clipping to deliver substantially more power than you would expect. Keep in mind that this is only a way to determine peak voltage potential. Average Power Now we can get into how a speaker really gets hurt. The key issue is average power over time. Let's get to the nitty gritty. The first key is understanding Crest Factor. "Crest Factor" is the difference between the average level of the signal and its peak level. A pure sine wave has a "crest factor" of 3dB, meaning that it's peak level is 3dB higher than its average level. We all know that 3dB represents a difference in power by a factor of 2. Another way to look at it is that the peak power of the signal is twice that of its average level. If we were to play a sine wave on our 50 watt amplifier, just below its clipping level, the average power over time the speaker would need to dissipate is 25 watts. On the other hand, a square wave has a crest factor of 0dB. In other words, its average power and peak power levels are equal. Our same 50 watt amplifier playing a square wave into our speaker requires the speaker to dissipate 50 watts. Keep in mind that this refers to sine and square waves only. Music has a much higher crest factor. Most widely available recordings have a crest factor of approximately 10dB. Looking at this in terms of power, the peak power is 10 times greater than the average power. If we were to play one of these recordings with our 50 watt amplifier when not clipping, the speaker needs to dissipate a mere 5 watts of average power over time. When the amplifier begins clipping, the peak level/power does not increase. BUT, the average power DOES increase. If we were to turn the volume up 6dB higher than the clipping level of our recording, we have reduced our crest factor to 4dB. Guess what? We are now needing the speaker to dissipate 20watts. This is four times the average power and four times the heat when measured over time. As you can see here, it is not the distortion or the waveform or anything along those lines that is killing your speaker; there is simply more average power over time. However, if the average power of time is still below what your speaker can handle, it doesn't matter if it's clipping or not. At higher power levels, the fact that a clipped signal carries more average power over time can result in damage. DC in Clipping One of the most famous myths regarding clipping is that it produces DC. The assumption is made because of the flat tops and bottoms to a square wave. It's incorrect to think of a squarewave as made up of positive and negative dc components. The only way for a it to be DC would be if there was a non-zero average value over long periods of time. If the polarity changes at all within the time frame that you are looking at, it is simply not DC. What are these flat portions of the signal? It is simply a combination of the fundamental frequency and all of it's higher order harmonics in sine wave form. For example, if you were to play a 20hz tone while clipping, there would be the fundamental frequency (ie. 20hz) and the second (40hz), third (80hz), and 4th (160hz) order harmonics. The sum of these frequencies creates what appears as a squarewave. There are two ways to test this for yourself; one is quite easy, the other is a little more advanced. The first way is simple if you have a variable crossover and an oscilloscope handy. Pass a low frequency square wave. You will notice the square shape on the oscilloscope. Now turn your crossover's low pass filter on. Slowly lower the setting as you approach the fundamental frequency. You will notice the waveform on your oscilloscope slowly rounding off into a typical sinewave. Once you have reached the fundamental frequency, your oscilloscope will show a perfect sinewave. The second way is for your math guys (or for those who like to use Matlab). If you look in the frequency domain using a Fast Fourier Transform, you will see the fundamental frequency and its higher order harmonics only. There will be absolutely no DC present. Clipping and the still voice coil The final myth is that of the still voice coil. It is perhaps the most believed myth regarding clipping. The idea is that because of the square wave, the coil is not moving during the flat portions of the signal. This is simply not true for a variety of reasons. The speaker does exhibit mechanical damping and remains in constant motion. Assuming the same voltage and excursion xmax, the cooling at any given frequency will remain the same, whether the signal is clipped or unclipped. Here is a great article to read on the cooling effects and how a driver fails under various waveforms: http://forum.carstereos.org/f-car-audio-49/t-clipping-test-results-47441" rel="nofollow - http://forum.carstereos.org/f-car-audio ... ults-47441 Summary To provide a final review of all that we have discussed on this topic, there are only two ways to damage a speaker: Mechanically and Thermally. The only way to do this is by applying too much input power in a given enclosure (mechanically) or too much average power over time (thermally). There is no DC in a clipped signal; the coil does not stand still; air passing over the coil (and thus cooling) is the same regardless of the waveform; and clipping is acceptable provided that the average power over time is lower than the speaker's limits. The next time you hear those famed words "your speakers died because of clipping", remember what you have learned, and above all, keep searching for the truth. It's out there somewhere. |
Posted By: Conanski
Date Posted: 13 May 2012 at 8:45pm
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The answer is yes but like everything audio related the answer comes with qualifiers.
Delicate high frequency drivers are easier to blow with amp clipping than big hairy woofers but it also comes down to the total power developed when an amp is driven into clipping.. it's got nothing to do with the distortion that is developed. If distortion killled speakers then every guitar amp ever made would instantly vaporise the second a distortion peddle was plugged in, but of course that does not happen. SO.. it's overpowering that melts voice coils and it's pretty easy to double an amps rated power output with heavy clipping so the bigger the amp the more careful you have to be. It also depends how close the two devices are in rated power, so for example a 50w amp could easily blow a 100w CD but connected to a 250w woofer the amp would die before the driver is harmed.
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Posted By: Conanski
Date Posted: 13 May 2012 at 8:49pm
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cyte wrote:Posted By: Blaize110
Date Posted: 13 May 2012 at 9:04pm
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The text you copied out is basically how I understand the situation. Yes clipping is not the direct cause of speakers breaking, and you can drive a speaker with a completely clipping amp all day, as long as the speaker is rated high enough to cope with the power. But quite often, if the amp and speaker are of similar power ratings, then when the amp does start clipping, the inherent increase in power that comes with clipping, causes the speaker to melt from thermal overload. So in this situation, you could probably justify using the phrase. "Clipping broke the speaker". Ok, it was actually too much power causing a thermal overload, but that was caused by the clipping.
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Posted By: infrasound
Date Posted: 13 May 2012 at 9:06pm
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Yes, it is DC. It does not "freeze" the woofer cone due to the restorative forces of the suspension, but it does attempt to hold it there. I haven't got a bloody clue what this Bill is on about with his harmonics. The fact is that when you overload a transistor it holds up against the voltage rails until the input falls within the voltage limits.
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Posted By: Conanski
Date Posted: 13 May 2012 at 9:13pm
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Posted By: cyte
Date Posted: 13 May 2012 at 9:19pm
Play a low frequency square wave through a driver with no crossover/filter and the driver will stop moving during the peaks and troughs.
This is also true. Regardless of the mechanism (increased RMS power in a square wave or DC) the fact is clipping amplifiers DOES damage speakers. As usual Bill Fitzmaurice is pretending he knows more than professional designers in order sell more of his plans... And let's face it, using a car audio forum as a reference in an electronics discussion is not really a good look |
Posted By: Blaize110
Date Posted: 13 May 2012 at 9:44pm
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Hmm, just my musings here but: Surely in a sine wave, the cone is moving the same distance as it would during a square wave of the same amplitude, simply in a slower and more constant manner. Whereas with a square wave, it makes the entire distance move almost instantly. Assuming that the cooling is proportional to the total distance moved by the cone, then both sine and square waves should provide the same amount of cooling when averaged out. The other factor I guess it would come down to, is could the coil cope with not being cooled during that fraction of a second that it is being 'stopped'. Taking the example of a 50Hz wave, a sine wave is causing the coil to be moving all of the time, therefore providing cooling of some sorts. But a square wave cause the cone to be 'stopped' for 0.01s before moving it again. I don't know the relevant equations, but would guess it's not enough to cause complete thermal overload in that time. (Quotes on 'stopped' due to the fact that the cone wouldn't instantly stop as it would have some intertia) However, even if both waves provided equal cooling, then the square wave would ultimately carry more power and so require more cooling to prevent thermal overload.
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Posted By: BUZguy
Date Posted: 13 May 2012 at 9:58pm
| you could look at it like this - say you had a 100w rms speaker and run it with a 100w amp unclipped. then suppose you run the amp so hard into clip that it produced, say 200w of distorted power. let's say that the driver worked for a few mins and then burned the voice coil out. this happens because 200w of thermal power dissipated in the coil was enough to take out the driver. if you took a 2nd amp, say capable of 500w and run this at exactly 200w, if 200w is the power at which the voice coil has reached its limit of temp, then similarly this would burn up at 200w too. the 2nd amp was not clipping but it still killed the driver. so it is power overload that kills speakers, whether the high power came from a clipped amp or not. |
Posted By: nomercy82
Date Posted: 13 May 2012 at 10:54pm
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I'd go with a resounding yes. Clipping an amp does cause damage, as to the specifics If I recall it sends the drivers to or past xmax, causing them to move in a non linear motion. Leading to mechanical failure. If clipping didn't damage speakers there wouldn't be anything like a compressor. ------------- Building a system in Pennsylvania. |
Posted By: Conanski
Date Posted: 13 May 2012 at 11:18pm
Like what 1 or 2hz? What has that got to do with audio? At any audible frequency the amount of time a driver spends "stationary" with a square wave input signal is inconsequential and even if this does happen it's not going to significantly factor into the stress levels experienced by the driver, no damage will result if the signal is within the power handling capacity of the driver. |
Posted By: soulray2
Date Posted: 14 May 2012 at 12:40am
No, this is rubbish! Only way too much power, (for a given enclosure, that is!), can cause mechanical failure, due to exceeding Xmax. It has nothing to do with clipping, which may cause failure due to overheating the VC, but that's really again because of excess power over a given period! ------------- "Moderation in all things, particularly moderation!" |
Posted By: audiomik
Date Posted: 14 May 2012 at 1:20am
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Hmmmm! Plenty of assumptions that an Audio program signal is entirely symmetrical. Unfortunately this isn't the case. Now lets consider the signal with say an asymmetry with more positive half cycle duration than negative. The current output of the Amplifier moves the coil forward (convention) in the magnet gap. Should this exceed the Xmax value of the 'Speaker being driven then the loss of magnetic field from the poles means a change in the impedance of the coil and a reduced cooling effect. Thus exceeding the 'Speaker's rating and will overheat the coil. In more extreme cases, exceeding Xmech, this will damage the mechanical structure of the 'Speaker. So when you overdrive your 'Speaker, the Current - this is the component of the Power being applied which actually moves the coil - behaves something like this in this 'Scope pic:  The sinewave signal is the Amplifier Voltage output and the clipped waveform in the center is the Current. Now should anyone then apply a clipped source signal to this same situation, especially one which is asymmetric, then you can easily see the effect which the current will have on the coil of the 'Speaker. At the point of destruction when the Amplifier Output was increased in the test result above, the current increased dramatically but unfortunately not for long enough to take a pic of the results before the 'Speaker coil failed completely. Please note: no I'm not going to deliberately wreck any more 'Speakers to get more results unless that is if someone else wants to provide them FOC for destruction! So, in answer to the Thread Title: "Does a clipping amp damage speakers?" then yes it certainly can, as does over-driving with an un-clipped signal above their rating in either case. And to comment on the content of earlier posts in this thread relating to Harmonics, it is the RMS Current applied directly to the coil which is the issue! Mik Edit: correction of parameters ------------- Warning! May contain Nuts plus springs, washers, screws, etc, etc. |
Posted By: nomercy82
Date Posted: 14 May 2012 at 1:35am
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The reason may not be as important as the result. Drive your amps into the clip range and just watch better yet listen to what happens to sound quality, and eventually your drivers. A 50 watt amp driven into clipping will eventually cook a speaker even if the speaker is a 100 watt rms speaker. ------------- Building a system in Pennsylvania. |
Posted By: GEB
Date Posted: 14 May 2012 at 10:09am
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Lot of differing 'facts' here! Problem is, who is correct? Is this Bill F experienced enough to provide this statement, or do the people opposing this out-qualify him? It was just a search for the truth really, not people's personal 'myths', or what they've 'read' on internet or been told by a 'mate' sort of thing! Some of which are obvious to everyone, even me!
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Posted By: swannie
Date Posted: 14 May 2012 at 10:14am
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Ok, not a technical answer, but one thing i would say after years of soundsystem install, hire & play.. If going by the red clip lights on amps, which is the only real way on the night at a gig weather the amp is clipping.. Many amps seem to be calibrated or set up differently. Some amps are happy to flash there red lights all night, with no bad issues.. (mild flash we are talking about) where as others (with the same paper/power spec) will crunch, pop & give the speaker a hard time under mild clipping. Also reading up on various amp test's it seems that many amps have different clip behavior dependent on design. One thing has to be said is that red lights are there for a reason.. bit like a rev counter on a car.. Always better to be running at 75% rather than 100% if you want it to live longer. as mentioned above, the most important factor.. Quality of sound. I always opt for amps at least 20% more power than i need, then limit the output via a compressor or speaker management system to avoid clipping of amps & over power of speakers, and giving enough headroom to cope with input voltage difference(220-240v), cable length & thickness & temp of the rooms its operating in. All of those factors can effect output power of amp, SPL you hear & weather the said amplifier is really 'clipping at 500w' lets say.. |
Posted By: GEB
Date Posted: 14 May 2012 at 10:28am
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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?
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Posted By: audiomik
Date Posted: 14 May 2012 at 10:47am
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Re: "Lot of differing 'facts' here! Problem is, who is correct?" The best way to find out is to read up on the Theory and then run some practical tests of your own to see the results..... A good starting point will be the Science of Moving Coils in Magnetic Fields - Faraday's Laws are a good starting point Mik ------------- Warning! May contain Nuts plus springs, washers, screws, etc, etc. |
Posted By: clvrdck
Date Posted: 14 May 2012 at 10:59am
if you had real DC going to your cones, you'd know about it.
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Posted By: infrasound
Date Posted: 14 May 2012 at 11:27am
 It's still a DC component within an AC waveform. Think about the time domain. |
Posted By: audiomik
Date Posted: 14 May 2012 at 11:32am
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Re: "There is not DC present in a clipped signal," unfortunately not necessarily true as there will be a DC offset created by an asymmetric signal driven into clip within an Amplifier, even after High Pass filtering. No DC component only occurs for a perfectly symmetrical signal but with Music where most signals are asymmetric then......... If you understand the Fourier Transform Maths then this offset is relatively easy to calculate as a Value..... The time related duration of the Lower Frequency components of a complex waveform, as in Music, and ultimately DC for the full series, is a function of the Current or Voltage offset created by the positive and negative half cycles of the waveform not being equal. (over simplified) This http://en.wikipedia.org/wiki/Fourier_transform" rel="nofollow - Link to Fourier Transform - Wikipedia will be informative. Another method of calculation is to integrate the waveform half cycles above and below the zero level and sum them..... This is what the 'Speaker coil does with the Amplifier Output signal fed to it so if the Areas under each half cycle of the waveform aren't equal then the coil doesn't 'return to zero'. Plenty of pages from a Search for "Asymmetric signal" will also provide information. My apology if this is technically somewhat beyond the Forum this Thread is located in, but it's a well known issue in Engineering circles  Mik ------------- Warning! May contain Nuts plus springs, washers, screws, etc, etc. |
Posted By: Liteworks
Date Posted: 14 May 2012 at 12:17pm
http://forum.qscaudio.com/forum/viewtopic.php?f=29&t=2736&sid=180d50fa225a6596013908b3a0e8f76b" rel="nofollow - Here's QSC's take on it: http://forum.qscaudio.com/forum/viewtopic.php?f=29&t=2736&sid=180d50fa225a6596013908b3a0e8f76b Similar to BFM's explanation, from a imo more respected source. -matt ------------- http://www.lite-works.co.uk" rel="nofollow - www.Lite-Works.co.uk My Kettle is 2000w! why isn't it very loud?? |
Posted By: _djk_
Date Posted: 14 May 2012 at 12:41pm
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"Is that the general jist of it?" You've got it! "It's still a DC component within an AC waveform. Think about the time domain." I've heard less intelligent remarks, I just can't remember when or where at the moment. http://forum.qscaudio.com/forum/viewtopic.php?f=29&t=2736&sid=180d50fa225a6596013908b3a0e8f76b" rel="nofollow - Here's QSC's take on it: Finally, something sensible. ------------- djk |
Posted By: Grubbah
Date Posted: 14 May 2012 at 12:55pm
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Newbie discussion huh ? I think this thread needs to be moved!
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Posted By: GEB
Date Posted: 14 May 2012 at 1:06pm
It'd be useful I think for people starting out to know the facts from the start, instead of being fed utter rubbish from some and spouting it out as fact for the rest of time for more people to be mislead. Some of the more long standing members should know better really! What else gets stated as fact to the unsuspecting!? Sticky maybe?
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Posted By: _djk_
Date Posted: 14 May 2012 at 1:11pm
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RaneNote 128 © 1991 Rane Corporation INTRODUCTION Power amplifier clipping is quite common. This note examines the clipping phenomenon which allegedly damages loudspeakers. We suggest that this form of distortion is not the cause. Rather, we show that amplitude compression of the audio spectrum is the culprit. Rane limiters provide a solution to amplitude compression, thus preventing loudspeaker failure. Monty Ross Rane Corporation Power Amplifier Clipping and its Effects on Loudspeaker Reliability • Harmonic Theory • Power Ratings • Blown Tweeters • Clipping and its Indicators • Limiter Protection RaneNote POWER AMPLIFIER CLIPPING AND ITS EFFECTS ON LOUDSPEAKER RELIABILITY WHY DO LOUDSPEAKERS NEED PROTECTING? All loudspeaker drivers have power handling limits. Once exceeded, damage occurs. There are several ways a loudspeaker suffers power damage. A couple of these warrant explanation. The first is over-excursion of the diaphragm. The diaphragm of a loudspeaker is the radiating surface that moves in response to an electrical signal. This surface may be conical, domed or flat in shape, and it creates sound by physically pushing and pulling the air in the room. The laws of physics say that in order to play louder or to reproduce lower frequencies, the diaphragm must move further toward its mechanical limits. If it is asked to move still farther, it experiences over-excursion. This most often occurs in woofers but can affect midranges or tweeters if low frequencies are not limited. If the loudspeaker cannot handle over-excursion, mechanical destruction of the driver is likely the result. Another enemy of loudspeakers is heat, generated bypower losses in the voice coils. No device is 100% efficient. For loudspeakers, 1 watt of input power does not produce 1 watt of acoustic energy. In fact most loudspeakers are typically well under 10% efficient [1] [3]. These losses convert to heat that builds up in the voice coils, causing mechanical deformation, like melting of the voice coil former. It causes weakening of the structure by charring the voice coil former, which later shakes apart. The heat causes the glues to bubble up, fill the air gap and glue the voice coil solidly in the gap. Often the voice coil wire melts like a fuse link, resulting in an open driver. Obviously we wish to prevent this.Music power-handling capability for multi-way loud-speakers always presents a problem to the loudspeaker user and designer. Users who must replace blown tweeters often feel they didn’t do anything wrong, because their amplifier only put out 50 watts and their speaker had a 200 watt rating.Yet, the tweeter blew up. This recurring problem motivated engineers to find out why this happens. Many opinions developed. Some of these have been scientifically verified— others remain theory. CONFLICTING “FACTS” Studies show the typical spectral energy for different types of music have high frequency energy considerably lower in level than low frequency energy [2]. This knowledge has further complicated the studies of how tweeters get destroyed. It seems that woofers should blow rather than tweeters if the high frequencies are lower in amplitude.Loudspeaker manufacturers use this knowledge about theenergy distribution of music when they design their products. This knowledge allows them to make better sounding tweeters because they can use lighter moving structures. Smaller wire in the voice coils can be used because there is significantly less power in the high frequency ranges. Since smaller wire is lighter, it takes less energy to move. For a speaker system rated to handle a given number of watts, the tweeter by itself can probably handle less than one-tenth that amount. From all this came a theory that spread quickly through the industry. Since there is more musical energy at low frequencies than high frequencies, there is not enough high frequency power to blow out tweeters. Therefore, high frequencies loud enough to burn out tweeters must come from somewhere else. Where do they come from? Well, it was reasoned, if there is enough low frequency energy to clip the amplifier, then it perhaps would produce enough high frequency distortion products (as a result of clipping) to blow up the tweeter. This theory convinced many in the early 70’s and slowly evolved into “fact”. While doing research into the reliability and protection of power amplifiers, I had to study how the)rewoPsuoenatnatsnI(sttaW001=Bd0,evaWerauqSzH001afosedutilpmAcinomraH.1elbaTcinomraHedutilpmABdnisttaWycneuqerF110001zH00120-80zH00233/145.9-21.11zH00340-80zH00455/189.31-4zH00560-80zH00677/19.61-40.2zH00780-80zH00899/11.91-32.1zH009010-80zHk11111/18.02-38.0zHk1.1210-80zHk2.13131/13.22-985.0zHk3.1:::::Amp Clipping-3typical consumer used amplifiers and speakers. I found that clipping is a common occurrence and is not as audible as most people think. I also found that the operation of many clipping indicators is very slow and does not always show actual clipping. (Many manufacturers slow them down, using their own rule of thumb for how much clipping can occur until it lights the indicator.) Newer and better sounding amplifiers, including amplifiers with soft clipping circuits, still blew tweeters. But amplifiers with higher power were having fewer incidences of blown tweeters. This appeared to reinforce the theory that clipping caused tweeter blowouts. One thing was clear, when clipping occurred, tweeters blew. If you’re getting the idea I don’t believe in the clipping/harmonic theory, you’re right. So let’s investigate the phenomena further. WHEN SINE WAVES CLIP When sine waves clip severely they resemble squarewaves in shape, introducing massive distortion. In the extreme case, a perfect square wave has the highest level of harmonic components (See Figure 1). A less clipped sine wave has components at the same frequencies but at lower levels. Let’s look at the square wave example shown in Table 1(at left). Fourier analysis shows the harmonic structure.As you can see, the total amount of instananeous powerleft to make it through an ideal 1kHz crossover (and on to the tweeter) is less than two watts (0.83 + 0.589 = 1.419W). Hardly a problem. And remember, this simulates severe overdrive of a 100 watt amplifier with a sine wave to make an ideal square wave. Driving it harder will not increase the harmonics.This analysis shows if a small tweeter that only handles 5or 10 watts is used in a 100 watt speaker system it would not blow out, even under square wave conditions. Yet it does. It takes a lot more than this to cause major failure. So what’s happening? Compression is what’s happening [3]. Today’s newer higher quality amplifiers have greaterdynamic range and sound better when clipped with musical transients than older amplifier designs. So it is more likely for a user to overdrive and clip newer amplifiers on low frequency dynamic peaks because of lower audible distortion. This results in compression of the dynamics of the music. The Figure 1. Harmonic Comnponents of a 100 Hz Squarewave vs. a 100 Hz Sinewave. Figure 2. Low Level, High Frequency Sinewave Mixed with a High Level, Low Frequency Sinewave Burst. Figure 3. 100 W Amp with 3 dB Overdrive Figure 4. 100 W Amp with 10 dB Overdrive Amp Clipping-403813 8-97high frequencies get louder but the low frequencies can’t. This may be heard as an increase in brightness of the sound. Some may simply interpret it as louder with no change in tonal balance. For example, in a 100 watt amplifier, as you turn up the level, the low frequency components will limit (clip) at 100 watts. Meanwhile the high frequency components continue to increase until they (the high frequencies) approach the 100 watt clipping point. The graphs in Figures 2, 3 & 4 are scaled in volts. With an8 ohm load the 100 watt level corresponds to 40 volts peak. Below clipping, the low frequencies reach 100 watts (40 volts peak) but the high frequencies are only 5 or 10 watts (9 to 13 volts peak).Let’s assume a musical signal with low and high frequency components driving a 100 watt (8 ohms) amplifier. We use a low level/high frequency sinewave mixed with a high level/low frequency sinewave burst. (See Figure 2). The high frequencies reproduced by the tweeter are at least 10 dB lower in level than the low frequencies. Now as we turn up the amplifier to clip the signal (3 dB overdrive—See Figure 3). Notice that only the low frequency burst portion of the waveform clips but the high frequency portion increases in level. The clipping, of course, produces harmonics but not nearly as much as the square waves discussed earlier. The amplitude of the high frequencies went up by 3 dB in relation to the low frequency fundamental. (3 dB compression). If you overdrive the amplifier by 10 dB, the high frequency amplitude goes up by 10 dB. This goes on dB for dB as you turn up the volume, until the high frequency reaches the 100 watt level. Meanwhile the peak level of the low frequency portion can not increase above 100 watts (See Figure 4). This now represents nearly 100% compression (no difference between HF amplitude and LF amplitude).Now it is easy to see how the high frequency portion exceeds the 5 or 10 watts tweeter rating. Sure, clipping is producing extra harmonics but they never approach the levels of the amplified high frequency source signals. It may be argued that the signal’s distortion would be intolerable. Don’t fool yourself. It really surprises people how much clipping they tolerate before they cannot listen anymore. Just disconnect the clipping indicator on a power amplifier and see how loud someone drives it. Watch the amplifier output with an oscilloscope. There will be a surprising level of clipping. 10 dB clipped off the top of low frequency transients is not an uncommon occurrence when the purpose is to impress your neighbors. ©Rane Corporation 10802 47th Ave. W., Mukilteo WA 98275-5098 USA TEL (425)355-6000 FAX (425)347-7757 WEB http://www.rane.com REFERENCES 1. K. Blair Benson, Audio Engineering Handbook,(McGraw-Hill, New York, 1988)2. R. A. Greiner and Jeff Eggars, “The Spectral AmplitudeDistribution of Selected Compact Discs,” Journal of the Audio Engineering Society, vol. 37, pp.346-275 (April, 1989)3. Carlo Zuccatti, “Thermal Parameters and Power Ratings ofLoudspeakers” Journal of the Audio Engineering Society, vol. 38, pp.34-39 (Jan-Feb, 1990) ------------- djk |
Posted By: SBC
Date Posted: 14 May 2012 at 1:13pm
+1  ------------- F.T.S.S. |
Posted By: _djk_
Date Posted: 14 May 2012 at 1:16pm
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To summarize, clipping does no harm unless: a) the long-term average power of the driver is exceeded b) mechanical damage occurs ------------- djk |
Posted By: GEB
Date Posted: 14 May 2012 at 1:24pm
Just a few points from QSC, although I'm sure some know better!  Clipping is bad for loudspeakers because it really heats up the voice coils. Myth. Clipping at any power level is capable of damaging your loudspeakers. Myth. Clipping is bad for loudspeakers because it is DC. Myth. Clipping is bad for loudspeakers because the sharp corners rip up speaker drivers. Myth. Clipping is bad for loudspeakers because the amp may put out more power than you expect. True. There you go folks!
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Posted By: Earplug
Date Posted: 14 May 2012 at 2:48pm
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. ------------- Earplugs Are For Wimps! |
Posted By: duck1
Date Posted: 14 May 2012 at 5:19pm
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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. |
Posted By: Liteworks
Date Posted: 14 May 2012 at 7:50pm
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 ------------- http://www.lite-works.co.uk" rel="nofollow - www.Lite-Works.co.uk My Kettle is 2000w! why isn't it very loud?? |
Posted By: GEB
Date Posted: 14 May 2012 at 8:20pm
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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Posted By: Peter Papp [PKN]
Date Posted: 14 May 2012 at 8:56pm
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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! |
Posted By: _djk_
Date Posted: 14 May 2012 at 9:06pm
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"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. ------------- djk |
Posted By: slaz
Date Posted: 14 May 2012 at 9:19pm
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 |
Posted By: Andy Kos
Date Posted: 14 May 2012 at 9:24pm
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Has anyone mentioned damping factor? Particularly in clip conditions? ------------- just a guy with a warehouse and a few speakers... www.bluearan.co.uk |
Posted By: Steve_B
Date Posted: 15 May 2012 at 1:08am
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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.” |
Posted By: _djk_
Date Posted: 15 May 2012 at 2:36am
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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.” ------------- djk |
Posted By: audiomik
Date Posted: 15 May 2012 at 12:13pm
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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. ------------- Warning! May contain Nuts plus springs, washers, screws, etc, etc. |
Posted By: soulray2
Date Posted: 15 May 2012 at 12:17pm
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! ------------- "Moderation in all things, particularly moderation!" |
Posted By: steve153
Date Posted: 15 May 2012 at 12:29pm
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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Posted By: JR.junior
Date Posted: 15 May 2012 at 12:50pm
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Yes, you'll get distortion. ------------- Support the scoop technology, larger mouth plays louder! |
Posted By: Earplug
Date Posted: 15 May 2012 at 2:51pm
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" rel="nofollow - http://forum.speakerplans.com/signal-chain-overload-effects_topic62868_page1.html?KW=distortion ------------- Earplugs Are For Wimps! |
Posted By: audiomik
Date Posted: 15 May 2012 at 11:25pm
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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 ------------- Warning! May contain Nuts plus springs, washers, screws, etc, etc. |
Posted By: Andy Kayll
Date Posted: 25 September 2012 at 5:11am
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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"> |
Posted By: snowflake
Date Posted: 28 September 2012 at 6:28am
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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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