New Article Debunking Some Speaker/Amp Myths - AVS Forum
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post #1 of 78 Old 06-05-2012, 04:38 AM - Thread Starter
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Debunking Some Speaker/Amp Myths:

http://sound.westhost.com/articles/speaker-failure.html

"Some Very Silly Myths

1. The Oscillations Myth
Since it is possible for an audio amplifier to oscillate at very high ( supersonic ) frequencies, it is widely assumed that this inaudible oscillation will silently damage woofers and instrument speakers in the same way that over powering does. So the story is often trotted out to explain burn voice coils. FACT: The vast majority of woofers and instrument speakers are immune from damage by inaudible high frequencies. The very high self inductance of the voice coil at frequencies at or above 20 kHz means the current flow is small and no serious heating can happen. Look at the JBL 2226 impedance curve - it's over 100 ohms at 20 kHz [1]

Damage to tweeters is possible and also to "twin cone" speakers with copper caps or rings attached to the pole piece.
High frequency oscillation at full power IS damaging to amplifiers. Smoke will appear as resistors and capacitors in output Zobel networks burn up and BJT amps will quickly expire as transistors fail from excess dissipation. Amps using lateral MOSFETs will normally survive such events with only slight damage. The causes of such oscillation lie with operator error and bad cabling practices.

2. The Clipping is Like DC Myth
Just as a woman cannot be a "little bit pregnant" - you cannot have little bits of DC. DC only comes in large and prolonged doses, anything else is AC.

The whole idea that clipped or flat topped waves have "little bits of DC" is complete nonsense, as is the even sillier idea that a cone is somehow rendered stationary whenever the drive wave is flat topped.

Clipping of an audio signal merely limits the peak amplitude and raises the average value - square shaped waves are just combinations of sine waves with many harmonics.

Note:

1. The pink noise used in the AES test is simply clipped to provide a 6 dB peak to RMS ratio. Natural pink noise has a 14 dB peak to RMS ratio. In case you missed the significance of that, the test signal recommended by the AES for power ratings is a deliberately CLIPPED signal !!

3. Smaller Amps are More Likely to Damage Speakers than Bigger Ones Myth
This naïve corollary to the clipping myth is also utterly wrong (see Figure 3). Since average power over time is what heats and burns a voice coil - a larger amp is always potentially more hazardous to a speaker. The popularity of 1000 watt plus per channel amplifiers relies on this complete nonsense being believed by a great many folk in pro audio.

It should hardly require any explanation - if you replace a smaller amp that is clipping with a bigger one that eliminates that clipping, then average power output must go up. This is shown clearly in Figure 3.

Likewise, we would hope that no-one would believe that a 50W amp driven hard into clipping (with a full-range signal) will damage a 500W speaker. Unfortunately, there appear to be people who do believe that is the case. In theory it might possible, but extremely unlikely."
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post #2 of 78 Old 06-05-2012, 05:25 AM
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Interesting article. I don't understand half of it, but I enjoyed reading it.
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post #3 of 78 Old 06-06-2012, 06:05 AM - Thread Starter
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Originally Posted by underminded999 View Post

Interesting article. I don't understand half of it, but I enjoyed reading it.

Got any specific questions?
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post #4 of 78 Old 06-06-2012, 06:40 AM
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Thanks for pointing out that some believe that you can feed your 250 Watt speakers 1000 watts and not suffer any ill effect. You can feed a driver enough clean power to overheat the voice coils.

An audiophile likes to talk about how much they spent and how good it sounds.

A DIY'er likes to talk about how little they spent and how good it sounds.

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post #5 of 78 Old 06-06-2012, 06:53 AM
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No direct questions, it's really about my understanding of the subject matter.

I get the idea of how a speaker is made. I like the diagrams and actually shots of the speaker coil, before, during, and after complete oblivion.

However, while I enjoy music/sound and the process to obtain the best sound for the best value in my personal system. When I start to see things broken down by watts, Hrtz, et all... I kinda gloss over. That says more about me, than about the article.

I do like to read these kind of articles, and my knowledge base is growing, but currently, I have not submersed myself deep enough to apply/use these for my own benefit.

I like what I like, and will use what I currently have until, either it quits working, or technology has progressed to the point that I have to jump forward.

For example, I ran the same 5. system since 1995 until last year.

The only reason I upgraded last year, was to incorporate BD's. So I upgraded my AVR to an early 2K's model that added 7.1. I added new surround speakers and a subwoofer.

However, I am still running the same mains and center channel that I had from '95.
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post #6 of 78 Old 06-06-2012, 07:24 AM - Thread Starter
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Originally Posted by Jinjuku View Post

Thanks for pointing out that some believe that you can feed your 250 Watt speakers 1000 watts and not suffer any ill effect. You can feed a driver enough clean power to overheat the voice coils.

Right. In the end it is power from the amplifier that overheats the voice coils. A larger amp increases the possibility of that happening. It is possible to have an amp that is so small that the speakers will never be damaged.

Back in the day when my two sons were teenagers and still living at home. I managed to keep my speakers intact by adjusting the system gain staging so that max volume was loud, but not damaging to the speakers.

In the end the most reliable form of speaker protection is the nut that holds the volume control. ;-)
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post #7 of 78 Old 06-06-2012, 10:07 AM
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Originally Posted by arnyk View Post

In the end the most reliable form of speaker protection is the nut that holds the volume control. ;-)

That is totally accurate...

However, Rod is entirely incorrect in his assertion that tweeters cannot be damaged by low power clipping stuff. I have personally experienced it, performed autopsies, and actually reported what happened to Selenium years ago. It was my TI205 tweeters.

When ultrasonic is driven into the tweeter, the voice coil itself did not overheat. That much Rod got correct. However, the voice coil wire broke as a result of cyclic fatigue.

The tweeter VC was manufactured by using the same wire of the coil as lead in and lead out. Unfortunately, they brought the leads out of the gap completely unsupported. As a result, there is flexure of the lead in and lead out wire where the lead wire is still exposed to the magnetic field of the gap. This flexure is of no concern as long as it occurs below the resonance of the unsupported wire. In all the cases I've had, the wire was resonated, and the wire broke after significant flexure to cause slip plane dislocation failure. If you examine the broken wire under a microscope, you will find that the surface texture of the wire near the break has frosted. Even closer examination witha metallurgical scope reveals the slip plane line structure characteristic of cyclic fatigue failure.

Bonding of the leads to the diaphram where it is exposed to the magnetic field of the gap is the solution.

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post #8 of 78 Old 06-06-2012, 02:24 PM
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You are absolutely right about high frequency ultrasonic oscillation being unlikely to damage speakers. On the other hand, AMPLIFIERS can overheat and be damaged due to ultrasonic oscillations.
A man I know who had his own amplifier company for many years (Audire), told me that most of the amplifiers that came in to him for repair were due to bad grounds on RCA input cables, which would cause the amplifier to oscillate and overheat and smoke the output transistors.
Some RCA cables, especially some of the more expensive machined ones, do not make good ground connections to the jack because they have no spring tension and may not fit tight.
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post #9 of 78 Old 06-07-2012, 04:46 AM
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I have had 2 cases of HF oscillation that have "damaged" speakers.

The first was in a Catolic church that had Community speakers installed. They never pushed the system hard.

About once year the highs would go out in the cabinets. The diaphragms were fine-but the light bulb protection was open.

After replacing the bulbs 3 times in 3 years I decided to take a closer look. When I put a scope on the output of the amps-I found a strong 60KHz oscillation.

After tracing it down and killing it (it was a ground switch on the foyer speakers of all things-it took awhile to find that one), they have not had a failure in 12 years.


Another case involved a resistor in the crossover burning out every couple of months. THis resistor was greatly over sized and should not be burning out. So we sent a friend in to investigate things-since the job was a good distance away.

He found a local radio station that was getting into the system and causing a strong 25Khz sine wave to be coming out ofhte amplifiers to the speakers.

He traced down the source of how it was getting into the system and there has not been a failure since. This has been around 2yrs ago.


I have heard of other cases of ultrasonc oscillations killing speakers-but these are the only cases I can document myself. It is rare-but it can-AND DOES- happen.

Danley Sound Labs

Physics-not fads
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post #10 of 78 Old 06-07-2012, 10:16 AM
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I think there is some confusion with respect to this article. The focus of the author is not the domain we live in. Here is his background:

"Phil Allison has worked as a pro audio designer, PA system and equipment trouble shooter and audio service tech for nearly 40 years. He has a strong interest in hi-fi sound reproduction and all technical aspects of live sound reinforcement, instrument amplification and disco music systems."

Sound reinforcement and instrument amplification is usually done differently than what we do at home. We can see this from one of his early comments:

"Back in the valve era, few people owned amplifiers with enough power output to overheat and damage typical speakers. Nowadays, amplifiers with output ratings in the many hundreds and even thousands of watts per channel are commonplace and can EASILY destroy any speaker ever made." Hundreds and thousands of watts? Clearly that is not a consumer scenario but live sound reinforcement. Why is that important? Because in those applications, high power amps (with supplies far more juicy than our 110 volt outlet) are used to power woofers alone, not a passively powered 2-way and 3-way consumer speaker. This is important because except for some indirect references, he is ignoring what happens when an amp clips and it is sending a signal through a crossover to both a woofer and a tweeter.

He notes correctly that a clipped signal generates tons of harmonics: "Clipping of an audio signal merely limits the peak amplitude and raises the average value - square shaped waves are just combinations of sine waves with many harmonics." If you have a 500 Hz tone and you don't clip, that is all the amp will be sending to the speaker. Clip that and now in frequency domain you will have the same 500 Hz tone but now combined with odd multiple harmonics of 1,500 Hz, 2,500 Hz, 3,500 Hz, etc. The low frequency tones go to the woofer which doesn't impact it much as it is designed to handle power. Not so with the little tweeter that is designed for profile of music, not a spray of high power harmonics. Translation is that the tweeter can and will get damaged then. In the active configuration in the pro world where the signal path is separate for the low and high frequencies this doesn't occur so is a non-issue for them. It is for us.

BTW, he notes later how high ultrasonics do damage tweeters, "Damage to tweeters is possible..." If ultrasonics can damage tweeters so can harmonics that reach there due to clipping.

Related to author's focus is the emphasis on reliability as opposed to absolute performance. He for example talks about bulb protection. This does work wonderfully and will keep the target device from destroying itself even in worst case situations. But the bulb can modulate with the signal just as he notes with other methods. If under normal use it is lighting up, it is doing that (may have to have a dark room to see it). He also says that fuses don't blow to protect tweeters. Maybe in high power sound reinforcement it doesn't do that but I can tell you from experience of having replaced the fuse in countless speakers that they do fail. And replacing them brings the speaker back to life (most of the time).

The author is clearly experienced and knows what he is talking about. The issue is to keep in mind who he is giving advice to and assumed architecture and performance goals. He is very clear with that in statements like this, "The popularity of 1000 watt plus per channel amplifiers relies on this complete nonsense being believed by a great many folk in pro audio." Look at your current gear. If it is not using 1,000 watts per channel to drive your speakers, you are not his audience smile.gif. Putting aside the clear reference to "folk in pro audio."

Sure, we have a lot in common with pro industry but there are differences that matter and one must keep that in mind when reading such articles.

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post #11 of 78 Old 06-07-2012, 01:12 PM
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Hundreds and thousands of watts? Clearly that is not a consumer scenario

150-200W amps are common and cheap and have been for years in home audio. Pro drivers are designed to be able to take much higher continuous power than most domestic drivers are - typically cooling of the motor has been an integral part of the design of the (pro) drivers for many years, which is far less so the case for even many of the better driver brands. Of late the better name brand drivers have been factoring this into their designs, but, most people would not be using these at home.

The JBL 2226 referenced in the article is rated at 600W long term, so it being driven by a 1kW amp is not disproportionate to a 100W domestic speaker being driven by a 150W amp. Or 100W amp, 60W speaker for that matter, so the effects are still entirely relevant to home designs, especially considering the generally better cooling of pro drivers.

Another point regards subwoofers. In recent years it is very common for HT people especially to use pro amps and 1kW especially bridged can be had in the US for a couple of hundred $ new today. Most sub drivers do not have well developed cooling systems in the mould of pro drivers so the generation of heat within the motors and high temps that come is easy to find, so the types of damage shown in the article would not be difficult to cause in domestic use. Or for that matter automotive use.

Related to author's focus is the emphasis on reliability as opposed to absolute performance.

Well, duh!. What's the title of the article? "Speaker Failure Analysis"
Nothing related to how to improve performance, just an analysis of how and why some are damaged.

with supplies far more juicy than our 110 volt outlet

Not everywhere in the world has a limited 110V supply. Rod's site is Australian based and we are 240V and with a typical domestic installation I have supplied over 3kW continuous into a load from an amp I own and not tripped the breaker. As this was a sine tone, I could have driven just about every driver available into thermal failure if that was my intent.
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post #12 of 78 Old 06-07-2012, 02:43 PM
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Quote:
Originally Posted by A9X-308 View Post

Hundreds and thousands of watts? Clearly that is not a consumer scenario
150-200W amps are common and cheap and have been for years in home audio.
150 to 200 is not my definition of "hundreds and thousands of watts" no matter which way you dice it.
Quote:
Pro drivers are designed to be able to take much higher continuous power than most domestic drivers are - typically cooling of the motor has been an integral part of the design of the (pro) drivers for many years, which is far less so the case for even many of the better driver brands. Of late the better name brand drivers have been factoring this into their designs, but, most people would not be using these at home.
That's right so be careful in reading pro articles and applying them to consumer gear. Different customer requirements create different design criteria. A speaker blowing up in a live concert can cost people serious money and their jobs/contracts. Not so at home.
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The JBL 2226 referenced in the article is rated at 600W long term, so it being driven by a 1kW amp is not disproportionate to a 100W domestic speaker being driven by a 150W amp. Or 100W amp, 60W speaker for that matter, so the effects are still entirely relevant to home designs, especially considering the generally better cooling of pro drivers.
None of this is related to the point I made. I said that in sound reinforcement folks are not likely using speaker with passive crossovers such as we do for the most part in home applications. This led the author, as he should for his intended market, to ignore what happens in non-active speaker applications where the tweeter would be subjected to clipping distortion. His points can and do apply to what happens to the woofer as you say, but not his overall message. Woofer <> speaker in consumer parlance whereas it very much can be in pro world.
Quote:
Related to author's focus is the emphasis on reliability as opposed to absolute performance.
Well, duh!. What's the title of the article? "Speaker Failure Analysis"
Nothing related to how to improve performance, just an analysis of how and why some are damaged.
That is just the first part of the article. The second part goes on to show schemes to protect the speakers and where there can be performance degradation, he notes it. I did the same by explaining that a bulb does provide maximum protection as he states but not talking about is performance issues shows a bias toward reliability over performance. For home consumers, that may not be the right trade off so it should be noted as I did.
Quote:
with supplies far more juicy than our 110 volt outlet
Not everywhere in the world has a limited 110V supply. Rod's site is Australian based and we are 240V and with a typical domestic installation I have supplied over 3kW continuous into a load from an amp I own and not tripped the breaker. As this was a sine tone, I could have driven just about every driver available into thermal failure if that was my intent.
Even with a 240 volt outlet you are far short of the assumptions he makes that thousands watts could be driving a single channel. Have you ever gone to a live concert venue and seen the kind of power that is provided? Nothing like your 240 home feed may apply smile.gif. I am confidently that if I surveyed home music listeners in Australia, only a tiny fraction would have active speakers and even smaller fraction with thousands of watts driving their single channels. Vast majority would be using passive speakers with one amp powering the whole unit and likely designed with limits of power in US, and not your 240 volt feed. I am not saying exceptions are not there but if we are to blow up "myths" we better make sure it applies to the masses. Having it apply to a few people with thousands of watts powering their speakers in active mode in Australia is not my idea of myth busting smile.gif.

Net, net, there is no myth that clipping can damage your speaker. It absolutely can if it is a traditional passive design. This can be shown even using the logic the author uses himself as he says ultrasonics oscillation can damage them.

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post #13 of 78 Old 06-08-2012, 07:10 AM - Thread Starter
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Quote:
Originally Posted by amirm View Post

He notes correctly that a clipped signal generates tons of harmonics:
"Clipping of an audio signal merely limits the peak amplitude and raises the average value - square shaped waves are just combinations of sine waves with many harmonics." If you have a 500 Hz tone and you don't clip, that is all the amp will be sending to the speaker. Clip that and now in frequency domain you will have the same 500 Hz tone but now combined with odd multiple harmonics of 1,500 Hz, 2,500 Hz, 3,500 Hz, etc.

While perfect clipping generates an unending series of odd harmonics, they decrease in size very rapdly:

401

For example, the first harmonic added is the third, but its amplitude is decreased to 1/3 and the energy it contains is decreased to 1/9. The next is the 5th, and now the energy is decreased to 1/25th or only 4%! The usual engineering criteria of 1/10th being easily ignored is almost satisfied by the first harmonic that is generated! The remaining ones are far less and decrease in size very rapidly.

Therefore the large number of harmonics generated should not be interpreted as meaning that they have a large amount of energy.

Therefore, clipping is not particularly hard on tweeters due to harmonic generation. Ever since we've been doing digital, it is very possible that the music has more high frequency energy than any harmonics generated by clipping.

Just things that some of us learned in one of our second year engineering courses, Amir. ;-)
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post #14 of 78 Old 06-08-2012, 07:21 AM - Thread Starter
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Quote:
Originally Posted by amirm View Post

150 to 200 is not my definition of "hundreds and thousands of watts" no matter which way you dice it.

I don't have to dice anything at all to see that calling 200 watts "Hundreds of watts" is far from excess hyperbole.

When we compare professional audio to consumer audio, it is often just a matter of scale. Pro audio speakers are often built more robustly, and are thus scaled up to handle the greater amounts of power that is commonly used with them.

Despite the false interpretation of the facts, the author of the paper mentioned in the OP is best known to those who know him as a person who works with consumer electronics and occasionally has pro audio projects delivered to him. His credential are good in both areas.

On another forum he mentioned that the loudspeaker driver that is the centerpiece of his article is from an AR2x which is a legacy consumer audio speaker. One tip-off is the fact that the voice coil diameter is only 40 mm - a voice coil from a speaker for professional audio (or a subwoofer for consumer audio) might be 4 inches or about 100 mm.
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post #15 of 78 Old 06-08-2012, 08:57 AM
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Quote:
Originally Posted by arnyk View Post

Therefore, clipping is not particularly hard on tweeters due to harmonic generation.

I have autopsied, diagnosed, and repaired tweeters which failed as a result of ultrasonic resonance of the lead wire. This is not the same as a dissipation failure, but a case of slip plane dislocation failure due to cyclic fatigue...

My oldest son did indeed provide me several instances of tweeter burnout of course on the exact same type of device, but the disassembly and analysis of those was consistent with the article pictures of a charred mess.

I'm sure that if the author of that article had more experience in actually disassembling failed tweeters, he would probably have learned what I know and relate here.

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post #16 of 78 Old 06-08-2012, 09:03 AM - Thread Starter
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Originally Posted by jneutron View Post

I have autopsied, diagnosed, and repaired tweeters which failed as a result of ultrasonic resonance of the lead wire. This is not the same as a dissipation failure, but a case of slip plane dislocation failure due to cyclic fatigue...
My oldest son did indeed provide me several instances of tweeter burnout of course on the exact same type of device, but the disassembly and analysis of those was consistent with the article pictures of a charred mess.
I'm sure that if the author of that article had more experience in actually disassembling failed tweeters, he would probably have learned what I know and relate here.
jn

What have you said that is inconsistent with the article mentioned in the OP?

How does one reliably determine the frequency of the signal that caused fracturing or overheating?
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post #17 of 78 Old 06-08-2012, 09:43 AM
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Quote:
Originally Posted by arnyk View Post

What have you said that is inconsistent with the article mentioned in the OP?
The article makes no mention at all about ultrasonic failure of the tweeter other than thermal. No mention whatsover...In fact, the article goes out of the way to show in essence that ultrasonics cannot do so as clipping doesn't contain enough energy, same slant you've taken..

Both of ya's is incorrect. That is inconsistent with real failures of real tweeters.. I have repaired about a dozen of those ev tweeters used in the old K horn set, T-50's or T-500's IIRC( EDIT: it was the EV T35...jn). Also, 2 Gauss-Cetec puppies, can't recall the model, but they had about a 5 inch diameter body with heatsinks on back. For more current tweets, the selenium D205TI's, I've repaired 6 of them for ultrasonic fatigue failure, and 2 for total thermal burnout.
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Originally Posted by arnyk View Post

How does one reliably determine the frequency of the signal that caused fracturing or overheating?

It's not overheating, it is fracture caused by cyclic fatigue failure from resonance.

For product which is hand assembled, the resonance frequency will depend on how the lead is dressed, it's length, how long it's in the gap flux, it's guage.. So even within one product line, I believe it would not be possible to analytically determine the frequency or frequencies (depending on the mode of the resonance). Across product lines, I would guess virtually impossible. It may be possible to get a range, but that doesn't help in the field.

To prevent it, address the failure mechanism. That would be the unsupported use of vc lead in/out wires which climb into the magnetic flux. I recommended to Selenium that they lay the wire against the diaphram and up the diaphram to vc former fillet, then bond it using epoxy or the polyimide the vc is assembled with.

edit: if you look at the pictures the author provided, note the lead in/out is held to the vc with masking tape. Not a well engineered solution, but for that particular vc assembly, there is probably no chance of resonance because of the coil inductance in the slot.

ps. I have worked on speakers where u/s oscillation toasted the VC's as well as destroyed the crossovers. Somebody had used a multiconductor snake to carry low level from the sources to the electronics, then used some of the twisted pairs to bring amplifier output back to the stage. Since all the pairs were in the same jacket, and they all had the same twist pitch, there was significant coupling between twisted pairs. Obviously, the person who installed it believed shielded twisted pairs cannot communicate magnetically.. Definitely incorrect when they have the same pitch.

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post #18 of 78 Old 06-08-2012, 12:18 PM - Thread Starter
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Originally Posted by jneutron View Post

The article makes no mention at all about ultrasonic failure of the tweeter other than thermal. No mention whatsover...In fact, the article goes out of the way to show in essence that ultrasonics cannot do so as clipping doesn't contain enough energy, same slant you've taken..

You have not answered my question - how do you know by looking at a broken driver that it was destroyed by power at a certain frequency?

As far as clipping destroying drivers, the math says that the most likely route is excess thermal dissipation due to the fact that square waves of a given peak amplitude (set by the power amp) have a lot more energy in them than the corresponding sine wave.

The spectral content of square waves, the energy content of square waves, and the fact that most tweeters have rising impedance at higher frequencies which will vastly reduce the energy actually dissipated in the voice coil are all due to laws of physics that I can't repeal. ;-) Don't blame me for them.
Quote:
Both of ya's is incorrect.

Prove it. So far all I see just a stack of unsupported assertions.
Quote:
That is inconsistent with real failures of real tweeters.. I have repaired about a dozen of those ev tweeters used in the old K horn set, T-50's or T-500's IIRC( EDIT: it was the EV T35...jn). Also, 2 Gauss-Cetec puppies, can't recall the model, but they had about a 5 inch diameter body with heatsinks on back. For more current tweets, the selenium D205TI's, I've repaired 6 of them for ultrasonic fatigue failure, and 2 for total thermal burnout.
It's not overheating, it is fracture caused by cyclic fatigue failure from resonance.

IME and that of people who have a ton more experience than I, cyclic fatigue is most commonly due to excessive excursion, which is far more likely to happen at lower frequencies than ultrasonic frequencies.

It's well known in the industry that if you start breaking tweeter voice coil wires, raising the crossover frequency or using a steeper slope can address the problem.
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post #19 of 78 Old 06-08-2012, 01:07 PM
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Originally Posted by arnyk View Post

You have not answered my question - how do you know by looking at a broken driver that it was destroyed by power at a certain frequency?
Arny, you did not ask that question.

The pictures presented in the article were simple dissipation failures. Flexure-failure as a result of resonance is an entirely different look.

First, you have to take the driver apart. If you find a break in the wire leading in or out of the tweeter coil form, but the coil is not thermally stressed, examine it at 60-200x under a metal scope or a really good stereoscope. Necking can be seen on the end of the wire, and the frosted slip plane deformation is there as well.
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Prove it. So far all I see just a stack of unsupported assertions.
If I knew then that I'd have to provide pictures to some goofball who has no mechanical engineering knowledge, I'd have done so. I just bought copper magnet wire, 2 part hi temp epoxy, and repaired the silly things under a microscope.

Unsupported assertions...You mean, like this unsupported assertion:
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Originally Posted by arnyk View Post

IME and that of people who have a ton more experience than I, cyclic fatigue is most commonly due to excessive excursion, which is far more likely to happen at lower frequencies than ultrasonic frequencies.
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Originally Posted by arnyk View Post

It's well known in the industry that if you start breaking tweeter voice coil wires, raising the crossover frequency or using a steeper slope can address the problem.
I love these blanket unsupported assertions as well.

For the tweeters I've repaired with lead cyclic fatigue, neither of these options will stop the problem..been there, done that. Raised the crossover from 3k to 5k, and 2nd order to third on the D205TI's I used.

The failure mechanism is the same thing that prevents one from cleaning military hi rel hermetic hybrids in an ultrasonic cleaner. The wirebonds flex under U/S vibrations, and this flexure causes exactly what I speak of.

Arny, please learn about the topic before asking questions. Until you do, you'll continue to ask questions of little meaning..


I'm afraid that every time I google it, I get IEEE documents which are not free. You may have better luck if you wish more info.

Search key words:

Ultrasonic cleaner
Military hybrid
high cycle fatigue
slip plane dislocation.
oops...almost forgot...bond wires.

The last time I saw it in a military hybrid, it was for the arming mechanism for a torpedo. For some reason, the customer refused to accept product with fatigue overstressed bond wires...go figure.

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Quote:
Originally Posted by jneutron View Post

Arny, you did not ask that question.

Please see post 16, this thread. Last sentence.


The pictures presented in the article were simple dissipation failures. Flexure-failure as a result of resonance is an entirely different look.
First, you have to take the driver apart. If you find a break in the wire leading in or out of the tweeter coil form, but the coil is not thermally stressed, examine it at 60-200x under a metal scope or a really good stereoscope. Necking can be seen on the end of the wire, and the frosted slip plane deformation is there as well.
If I knew then that I'd have to provide pictures to some goofball who has no mechanical engineering knowledge, I'd have done so. I just bought copper magnet wire, 2 part hi temp epoxy, and repaired the silly things under a microscope.
[/quote]

Necking?

You mean like this?

234

The picture is at http://www.sciencephoto.com/media/3677/view

The text under it agrees with my recollection of the meaning of the word "necking" in this context which is:

"Necking in copper wire. Copper wire that has been stretched to breaking point showing localised narrowing ("necking") around the break. The narrowing happens just before the wire fractures."

Necking around the break point in af wire is due to excess stretching due to tension, not metal fatique due to excess bending.

I would expect a fatigued wire's broken end to look like this:

157

Quote:
Arny, please learn about the topic before asking questions.

At least I know what fatigued wire looks like and what it's called!
Quote:
Until you do, you'll continue to ask questions of little meaning..
I'm afraid that every time I google it, I get IEEE documents which are not free. You may have better luck if you wish more info.
Search key words:
Ultrasonic cleaner
Military hybrid
high cycle fatigue
slip plane dislocation.
oops...almost forgot...bond wires.
The last time I saw it in a military hybrid, it was for the arming mechanism for a torpedo. For some reason, the customer refused to accept product with fatigue overstressed bond wires...go figure.
jn

So you think that the intensity of sound in a cleaner is comparable to sound in a tweeter whose voice coil is acting like an inductor and resisting current flow accordingly????
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post #21 of 78 Old 06-09-2012, 09:37 AM
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Quote:
Originally Posted by arnyk View Post

While perfect clipping generates an unending series of odd harmonics, they decrease in size very rapdly:
401
For example, the first harmonic added is the third, but its amplitude is decreased to 1/3 and the energy it contains is decreased to 1/9. The next is the 5th, and now the energy is decreased to 1/25th or only 4%! The usual engineering criteria of 1/10th being easily ignored is almost satisfied by the first harmonic that is generated! The remaining ones are far less and decrease in size very rapidly.
Thanks for the graph and equation Arny. The key thing to note here is that the tweeter doesn't seen individual spikes so your computation of their individual power ratios does not tell the whole story. The tweeter sees the sum total of all of them that is seen as input power to the tweeter (as would be the case with real music). If we add up the power of the first five harmonics, we get to 20% of the power of the original tone that created them.

20% of the low frequency spectrum is a lot of wattage because most of the music energy is in low frequencies. Here is the spectrum of a clip I picked at random from my library:
i-VrjGZj4-XL.png
Look at the amplitude for the energy at 2000 Hz. It is around -20 dB. Now look at its first odd harmonic at 6000 Hz. Its amplitude is -45 dB. Pretty large drop. Speaker designers take this into account by using much lower powered drivers for tweeters vs woofer. If you take 20% of the low frequency amplitude and dump it into high frequencies you significantly raise their amplitude floor and with it, increased energy overall per above computation.
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Therefore the large number of harmonics generated should not be interpreted as meaning that they have a large amount of energy. Therefore, clipping is not particularly hard on tweeters due to harmonic generation.
Well, the math and reality of music spectrum says otherwise. Regardless, this king of analysis should have been in the author’s paper and his reasoning for dismissing it explained. There is nothing there in this regard. He shows one graph that only has amplitude, not spectrum and no talk of tweeter impact.
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Ever since we've been doing digital, it is very possible that the music has more high frequency energy than any harmonics generated by clipping.
More the reason then to not dump additional energy from bass frequencies on top of them!
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Just things that some of us learned in one of our second year engineering courses, Amir. ;-)
None of this, including your and my analysis is enough to actually debunk the myth the article sets out to do. Failure analysis must include manufacturing and field data. It needs to include the type of analysis that JN performed.

The author is hypothesizing the sources of problem and analyzing them. In this case, I believe incompletely so with respect to consumer scenarios. Such analysis would only be the first step in figuring out what could be happening. He may be making assumptions that are incorrect. The only way you would know that is as I mentioned: examining large number of failures across many brands and designs to see if the hypothesis is true.

So no, just taking engineering classes teaches you little in this regard. I happen to have caught the assumption that he is using active designs and ignoring the impact on passive speakers. How many other assumptions may have been missed that a manufacturer and designer of speakers would know that the author did not?

Again, let me emphasize that I think the author is a skilled engineer and there is useful data in what he wrote. Just want to make sure we don’t run off with it and give poor advice to readers here who may then damage their speakers because they think it is harmless to turn up the volume to clipping. It is not. It will damage their speakers. I have repaired too many speakers on Mondays after the weekend party where the volume was turned "past 11" to accept this other wise smile.gif.

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post #22 of 78 Old 06-09-2012, 09:52 AM
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There are a couple of other considerations:

1. While the harmonic series of a square wave drops off fairly quickly, remember the crossover network in most speakers will roll off the low-frequency energy before the tweeter sees it. thus, the added energy at the tweeter from clipping can be significant.

2. The average power of a square wave (e.g. clipped signal) is higher than that of a sine wave.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #23 of 78 Old 06-09-2012, 12:06 PM
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Quote:
Originally Posted by DonH50 View Post

There are a couple of other considerations:
1. While the harmonic series of a square wave drops off fairly quickly, remember the crossover network in most speakers will roll off the low-frequency energy before the tweeter sees it. thus, the added energy at the tweeter from clipping can be significant.
2. The average power of a square wave (e.g. clipped signal) is higher than that of a sine wave.

One can also bring into the eqation that "normal sound/music" has a spectrum that roll off about 3 db/oct,from low to high, i.e. there is conciderably more "energy" in the lower regions than the higher. However, driving excessive energy into the tweeter will first and foremost make you turn down the volume -it will sound harsh and abrasive, especially on recordings with good dynamics (the stuff we live for smile.gif).

If I had to choose between a system with an amp clipping well before the speakers and a system with speakers bottoming out well before the amp, I would allmost certainly go for the over-dimensioned amp system.

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post #24 of 78 Old 06-09-2012, 01:23 PM
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When considering the power of harmonics in a clipped sine-wave, there is a problem using square-waves for analysis: The harmonic content is not necessarily similar.

As you add each progressive harmonic to a sine-wave, the top does indeed get flatter and the rise/fall times do shorten, but only with the higher harmonics does the slope approach vertical. It is the steep rise/fall times that contain the energy of the higher harmonics.

When a sine-wave is driven into clipping, the "flat-top" is an added DC component in the frequency domain. The steeper rise/fall times add the harmonics. A slightly clipped signal would have very little added harmonics, a moderately clipped signal would have some of the lower harmonics added, and only an grossly clipped signal would have the higher harmonics added.

Of course, if the fundamental frequency is high to begin with, it doesn't take many harmonics to creep above the audible range. As Arny pointed out, these lower harmonics will contain more energy than the higher harmonics. So if the tweeter damage that John alluded to is indeed caused by clipping, it would likely be from the clipping of higher frequencies.

This is easily observed by watching a spectrum analyzer as you drive a sine-wave into clipping.
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post #25 of 78 Old 06-09-2012, 07:12 PM
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Back in my B&W days we had a customer who called to say there is something wrong with his 801's. He noticed his tweeter moving during a passage from I believe Stravinsky The Firebird CD (Telarc?).

Purchased the CD, noted the tweeter motion, and took a look at the waveform. There was a pulse train of triangle waves when this instrument (trumpet?) was played (sounded like spitting into the mouthpiece). The tweeter was moving (maybe around 40 hz) in relation to the frequency of the pulses.

Crossovers are not smart enough to know the difference between the high freq content of the waves and their period.smile.gif

Be the sage.
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post #26 of 78 Old 06-09-2012, 09:52 PM
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Quote:
Originally Posted by amirm View Post

I have repaired too many speakers on Mondays after the weekend party where the volume was turned "past 11" to accept this other wise smile.gif.
Man, I love that story. Old Bill really knew how to throw a party! Remember the one on Paul Allen's yacht when they got pics of you doing jello shots off of Lisa Lamponelli? Or how about the time during that meeting when everyone was doing bong hits and orange sunshine and decided that blu-ray was just dumb? Those were the days my friend. We thought they'd never end.
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post #27 of 78 Old 06-10-2012, 04:33 AM - Thread Starter
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As the Christian scriptures say:

John 8:32

"Then you will know the truth, and the truth will set you free.”

What really happens when you clip the !@*%!! out of music?


536

So what is this?

I took the signature drum/guitar/bass passage from "Mustang Sally" and first converted it into a FS normalized mono, 192 KHz 16 bit wav file.

I then amplified it by the indicated amounts, which produced first distorted and then horribly distorted, and ultimately ruinously distorted music.

So what happened to the the spectral contents of the music when it was clipped?

What we see is pretty much 4 parallel lines above 30 Hz and up to 22 KHz. This indicates essentially the same proportioning of spectral energy up to the 22 KHz cut off of the original sample.

Above 22 KHz we see that high frequency content has been added, but at far smaller amplitudes than any of the music, and at an amplitude that continues to decrease with frequency.

I would say yet more audiophile myths demolished!

The cause - it is an apparently little known scientific fact (that I have posted here several times before) that nonlinear distortion of complex waves creates both IM and Harmonics. In this case the IM dominates and tends to preserve the spectral balance of the music. The harmonics that are generated explain the energy above 22 KHz, which is relatively minor, less than the music and pretty much innocuous.

Added on 6-11:

Same treatment to a heavily compressed and clipped segment from a more contemporary recording - Owl City's "Shooting Star":

538

Note that the recording, being already compressed, puts the lines closer together, but they are still essentially parallel from 50 Hz-20 KHz.
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post #28 of 78 Old 06-11-2012, 06:20 AM
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As I previously asked you Arny, Please learn the subject. It's clear that your attempting to use google to bolster your argument, but you are failing.
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Originally Posted by arnyk@pcavtech View Post

Necking?
You mean like this?
234

No. Not like that.

That is a picture of a wire that has been PULLED to breaking. AND, that is exactly what the article said was done to the wire..
Nice picture, but not what I've been talking about.

Please learn the subject... You are presenting yourself shall we say, not in a very good light?

Go back and google again, but this time look for words like cyclic fatigue, slip plane deformation, resosnant mode failure, wire bonds...

This is rudimentary knowledge taught as one of the core courses in an engineering degree.. Why do you not know or understand this??
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Originally Posted by arnyk@pcavtech View Post

At least I know what fatigued wire looks like and what it's called!
No, all you've proven is that you can google stuff . You've not shown that you have the ability to discern whether or not the content is consistent with the discussion.
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Originally Posted by arnyk@pcavtech View Post

So you think that the intensity of sound in a cleaner is comparable to sound in a tweeter whose voice coil is acting like an inductor and resisting current flow accordingly????
Are you kidding? You've no idea how an ultrasonic cleaner works, you have no idea what resonance of a wire is, you've no idea what high cycle fatigue is.

Arny, either learn the subject, or ask questions.

Sigh. That's the biggest problem with the internet and information. Anybody can google and find stuff, but many people do not have the intellectual skills to discern accuracy.

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post #29 of 78 Old 06-11-2012, 06:49 AM - Thread Starter
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As I previously asked you Arny, Please learn the subject.

So JN what have you got to teach?

I see nothing but vague references and unsupported assertions.

You never did explain why you misused the terminology of an area of Science that you claim to have superior knowlege of.

I aced my university level metallurgy courses so I know what these failure modes look like. I just found the pictures to match, whose associated text just happened to agree with what I learned way back when. Basics like the ones you fouled out on, haven't changed that much.

Come on big boy, show us some good stuff - relevant facts from independent authoritative sources like I did. ;-)
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post #30 of 78 Old 06-11-2012, 07:14 AM
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Originally Posted by arnyk View Post

So JN what have you got to teach?
Apparently with respect to you, english as a second language.. But we already know your schtick. Anything you can't discuss, you divert the discussion away. Here, you can't discuss cyclic fatigue failure, so are trying to divert it to simple tensile failure..
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Originally Posted by arnyk View Post

I see nothing but vague references and unsupported assertions.

Nothing vague at all. You are attempting to divert the discussion away from the actual science of high cycle fatigue failure of a wire flexing at ultrasonic frequencies, to one that you have been able to google.

So, this diversionary statement speaks for itself..
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Originally Posted by arnyk View Post

You never did explain why you misused the terminology of an area of Science that you claim to have superior knowlege of.
Again with the diversionary tactics. Please learn the topic..
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Originally Posted by arnyk View Post


I aced my university level metallurgy courses so I know what these failure modes look like.
That's an unsupported assertion. AND, your posts certainly do not reflect any understanding which one could mistake for "aced".
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Originally Posted by arnyk View Post

I just found the pictures to match, whose associated text just happened to agree with what I learned way back when.
You posted a picture of a squirrel, and are continuing to divert.

Everybody sees it Arny.

I gave you the key words for a google search. Go for it.

It's truly amazing the depths you will go to rather than admit you've no idea what the topic is. It's a failing of yours that's been talked about for a decade (that I'm aware of.)

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