Power Handling

[ninohernes]

How is the power handling of a loudspeaker determined? Do they just play the speaker until it stops? or is there some mathmatical equation that determines how much power a given speaker can handle. How did AR determine power handling, and did they do any power related experements?

[Guest Nigel]

Hi Joe;

The typical power handling numbers typically published are, more or less guess. DIN has a very structured tested that is very repeatable, and the speakers are driven to failure. The DIN test is much tougher than music on the speakers.

On AR speakers (the ones that this group is interested anyway), playing music, the primary cause of speaker damage is inadequate amplifers clipping. AR speakers with 12" woofers will handle very powerful amplifiers. On the live vs AR demos with AR10pi/AR11 speakers, the amplifiers were 1000 Watts each.......

[soundminded]

I have had this discussion repeatedly about amplifier clipping especially as related to tweeter damage. The fourier analysis would show that clipped waveforms would produce substantially higher levels of harmonic components than is typical for normal music therefore driving the tweeters much harder. Yet many people maintain that this is still insufficient to damage most tweeters under most conditions of such abuse. Do you have any experience or evidence to back up the notion that overdriving inadequate power amplifiers is a major cause of tweeter or other driver damage?

BTW, for anyone who isn't aware of it, when a manufacturer gives a single maximum wattage rating for a loudspeaker system, it is almost always for the woofer which invariably has the greatest capacity and is usually driven the hardest by most types of music.

[Guest Sean]

The German / European DIN standards set forth specific testing procedures as to how power handling is to be tested and rated. AR gave both DIN and "standard" power ratings for the AR 9's in their owner's manual. As a general rule, DIN ratings are very conservative ( as most German's are ) and this was quite evident when you compared the two. The DIN rating was quoted at 180 watts for the specified duty cycles and the "standard" rating was quoted as 400 watts with less than 10% clipping. Given that i have driven an amp rated at 1200 wpc ( and actually clips at 1450+ per channel ) into thermal overload on two different occasions without blowing up my 9's, that should tell you something. Yes, it was VERY loud and YES, the 9's are built to take it : ) Sean

>

PS... My experience is that the upper midrange dome on the 9's tends to blow before any of the other drivers will.

[soundminded]

"PS... My experience is that the upper midrange dome on the 9's tends to blow before any of the other drivers will."

When that happens, that must be a very disappointing experience. It gives you one of those Ah $--t days.

[Guest Nigel]

>Do you have any experience or evidence to back up

>the notion that overdriving inadequate power amplifiers is a

>major cause of tweeter or other driver damage?

In college dorm, 20+ years ago, with Advent being driven by a 40W per channel Onkyo receiver.....

[kkantor]

"Guess" would be one way to put it. Certainly there is no mathematical way to ascertain power handling, as too many factors are involved to allow a clear-cut definition.

There are various pass/fail test standards, but they are most usefully applied to assuring the consistency of individual drivers in a manufacturing environment, and really don't adequately address the questions that are paramount to the user: how big an amp do I need, and how do I know if I am over-driving my speakers? If you like to listen loud, the best thing to do is put your hand on the face of the drivers now and then, and turn the music way down if you feel any heat at all.

At worst, companies use the power handling spec to try and impress their customers. At best, manufacturers are trying to suggest to customers what an appropriate matching amplifier would be.

I don't believe in the "small amps make tweeters blow" story at all. It was made up by the marketing people at AR to give dealers something to say as the first wave of really big power amps hit the streets, and many speaker companies scrambled to alter their designs.

No way that the clipping math works out. Not even close. Even if the music is clipped beyond any point of intelligiblity (and I'm talking like a rocker, not an audiophile here), the additional load on the tweeter compared to baseband heating is not significant. It was a clever defense strategy however. Many still believe it.

If you doubt me, try intentionally blowing your tweeters, one channel with a 50 Watt amp and one channel with a 200 Watt amp.

[kkantor]

For a demonstration many will find hard to believe, I did the following this evening:

1- Took a snippet of a Beatle song I recorded with an old band of mine.

2- Uploaded the snippet as a WAV file.

3- Uploaded the average spectrum of the snippet as a WAV files.

4- Raised the gain of the snippet, causing significant, but not horrible 0 dB clipping.

5- Uploaded the clipped snippet as a WAV.

6- Uploaded the average spectrum of the clipped snippet.

Let's discuss, eh?

http://www.aural.org/ar_hist/clipping/

[Guest Brian_D]

I always assumed the clipping problem (which causes dammage to drivers) was a result of clipping in the output section of the amplifier. (When signal to the speaker becomes essentialy DC)

Speakers get clipped waveforms inherent in the program all the time (any guitar with a distortion pedal or effect) and that doesn't neccesarily mean the output is "clipped" or being driven beyond its electrical limits. Look at a guitar amp. There are lots of amps in service still that have a distortion pedal glued right to them that have seen nothing but clipped signals since day one. Yet you only hear of dead guitar amps when they've been overdriven.

Ken, I don't want to be disrespectful, and you have textbooks of knowledge in that cranium of yours that I'll never have, but... I don't think that your clipped waveform test is valid. If the signal is clipped, but the output of the amplifier is within its electrical limits, you'll never blow the speaker.

When an amplifiers output becomes DC, all the drivers get the voltage becasue it's (non-existant) oscilation isn't likely to be filtered by any of the crossover components. So if you want to make this test valid, use that same clip and then increase the output of the amp and monitor with a scope until it looks like the one you edited. DC is DC my friend, and the speakers that don't have the susspension to handle the excursion or the motor structure to handle the heat will fail for any one of several reasons.

I've been in the DJ business for lots of years. I've killed lots of tweeters. I stopped killing tweeters when I switched to higher-power amplifiers. The music didn't change, the speakers didn't change and I certainly didn't play them any quieter! I have to believe that the low-power amplifiers were causing the tweeters to fail.

-Brian

[soundminded]

Here's my take.

When an amplifier is driven to clipping, the amplifier output stage devices keeps switching rapidly between cutoff and saturation. Since the only part of the waveform on each half cycle that is actually still in the linear mode is the transient attack, the harder the amplifier is driven into clipping, the greater the percentage the first part of the transient attack is to the total waveform thereby decreasing rise time to saturation on each half cycle. The fourier analysis of this type of waveform as the amplifier is driven harder into clipping is that it is very rich in high fequency components. The amplifier is litterally operating at maximum power dumping most or all of its available power into the tweeters. Several things can happen. One thing that can happen is that the amplifier's protective circuits can cut in and shut the amplifier down. Depending on the circuit, the shutdown could be brief until the amplifier recovers from overload or extended until the output cools down, or until a circuit trip mechanism such as a fuse is replaced. The amplifier could continue to deliver power to the tweeters and they could either absorb it without damage if their 100% duty cycle capacatity exceeds the amplifier's capabilities or the tweeters could fail in one of several possible modes. Often the voice coils will just melt. Banks of piezo tweeter seem very rugged and are I think are more immune to failure than electrodynamic tweeters. Unfortunately they are highly directional and not very musical. If the current is great enough, it may also be possible to damage the crossover network coils.

If the amplifier is well designed, it will not usually exceed its maximum capability, it will either be restricted to it or shut down to protect itself.

A substantially more powerful amplifier can avoid clipping but if the speakers are driven too hard, then the other drivers are put at risk as well.

[Guest Brian_D]

Yeah, what he said.

(FYI) no piezo's in my PA or Program speakers. Once had some in some stage monitors, but they got a beer poured down them.

Also, remember the old Soundcraftsmen amplifiers? They were called the "woofer killers" by us DJ guys. I recently destroyed one of those driving a pair of CV Earthquake Jr.'s... the overload light came on but it kept playing for a good 5 minutes. I found out later that it had gone into thermal overload fairly regularly, and the previous owner had "jumpered" the circuit. (jumpered = stuck a 1/4" bolt in the fuse spot) Sparks, smoke and no subs for 30 minutes... nice.

-Brian

[soundminded]

The strangest case of amplifier overload I ever saw was in a public address system that someone had recently installed for a 650,000 square foot facility. When the fire department went to test it, it failed miserably with short spurts of speech being cut off intermittently. Somehow fixing public address systems that other guy installed and screwed up always became my project, now I wonder why. This was a 70 volt system and there were 5 buildings the largest of which was an 11 story high rise. Whoever had designed this system must have been the dumbest bunny in the litter. Although there were banks and banks and banks of 300 watt Johnson Controls audio amplifiers, only one amplifier was dedicated to the entire instant voice PA system, only one to the instant alarm system, and the rest were all dedicated to an automatic 10 minute delay alarm which stayed in a standby mode doing absolutely nothing. What was happening was that the one PA amplifier when addressing more than a few floors (100 watts maximum load per floor, most speakers on 1/2 watt taps, all were 8" ceiling mounted Soundoliers) the amplifiers would go within a second or two into an overload condition, shut down for a few seconds, come back on, overload again indefinitely. Same for the alarms. All that was required was to reconfigure the amplifiers so that they would no longer overload. When I was done, half were dedicated to the PA system and half to instant alarm system(the alarm mode would override the PA mode. Why didn't both modes use the same amplifiers? Beats me, maybe JC was able to sell them a lot more amplifiers that way. Or maybe the fire code requires dedicated amplifiers for alarms only. Don't know. Anyway, that's what happens when you really really really drive an amp to clipping. Good thing though, no tweeters to burn out.

[Guest Bret]

>The fourier analysis of this type of waveform as the amplifier is driven harder into clipping is that it is very rich in high fequency components.<

But does that even matter - the "rich in high frequency" part? IF I were to take my 9s out and attach 'em to a deep-cycle marine battery, is it the frequency that gets 'em or is it the DC current that'll turn the tweeters' voice coils into copper ingots first because they are smallest?

BTW, if you use a marine battery, at least the speakers are near the boat. . . you know, to be used as anchors.

Bret

[Guest Bret]

>In college dorm, 20+ years ago, with Advent being driven by a 40W per channel Onkyo receiver.....<

Anecdotal evidence may be "no evidence at all" but it was very rare (I can only think of twice, and one of those times was me) that I had to replace AR tweeters when the speakers were driven by a big amplifier.

Bret

[soundminded]

DC is zero hertz. the capacitor which prevents low frequency energy from getting to the tweeter will block current in the circuit completely. (That's how many solid state amplifiers prevent dc bias voltage on the output transistors from damaging loudspeakers.) However, if you suddenly close the circuit on a battery, a tweeter, and a capacitor in series, the sudden change from zero volts to the battery voltage is a step function. This has a very high frequency component. If this does not damage the tweeter with high "inrush current" the capacitor will become polarized and no further current will flow. If you bring the dc volatage up slowly with a rheostat, then the battery will not damage the tweeter (assuming the capacitor doesn't leak. But heaven help you if you accidently jump out the capacitor. Then PFFFFF no more tweeter.

[kkantor]

Disagreement isn't disrespect! In fact, I find your data point interesting, although you and I have opposite experiences. When you talk about switching from low to high power, are you talking about several different models of amps, or from one kind of low power to one kind of high power?

Surely, there were amps that had output pathologies when they were clipped, but with most amps you can't distinguish a clipped input from a clipped output. If anything, the clipped output is a bit milder in terms of HF content ("soft" clipping). So I do believe the experiment is valid.

Where I disagree with you more directly is the idea of "DC". I've never seen an amp that produces DC when clipped, and I can't see what DC would have to do with tweeters anyway. That would blow woofers. What was claimed to blow tweeters was an increase in HF caused by the "squaring off" of waveform tops, and you will find exactly that in my processed file.

I did this experiment on a laptop from a hotel room. When I get back to the lab next week, I will record actual waveforms from actually clipped power amps to show you. They will look essentially the same.

(If you don't mind, I'd rather not do this with my big Crowns. Even my dummy load won't take that...)

[kkantor]

Hmmm... it doesn' really work this way. Attaching a battery to a capacitor is a "step function". This does NOT result in more high frequency energy due to "inrush current" compared to a sine wave within the passband of the crossover. It just doesn't. A linear filter works the same way, regardless of whether the input is transient or not. What matters is the power spectrum of the signal.

Since you referred to "Fourier Analysis," I suggest you do a couple:

- analyze the spectrum of connecting a 10 Volt DC source to a RC network with a corner of, say, 2 KHz.

- analyze the spectrum of a 10 Volt peak sinewave above 2 KHz.

Then tell me which will heat the tweeter 100 times more. You CAN'T blow tweeters with DC if they have reasonable crossovers. It cannot be done. You could connect hundreds of volts of DC to the tweeter crossover of an AR9 once every thirty seconds, and the voice coil wouldn't get warm. This isn't speculation or theory. It's fact.

[Guest Bret]

>DC is zero hertz. the capacitor which prevents low frequency energy from getting to the tweeter will block current in the circuit completely. <

Well, you see there, I just keep learning things.

Maybe, just maybe, my anecdotal experience is that cheap amps blow tweeters and it has nothing at all to do with waveform or DC.

If the capacitor won't pass DC, then obviously even a really nasty DC current couldn't get to the tweeter, meaning that DC cannot be the culprit.

I remember Peavey used to run an ad about being able to put a cigarette out on the voice coil in one of their PA speakers. I think the idea was that the voice coil wouldn't smoke. . . (sorry).

So what is it that would produce voice-coil melting heat in a tweeter motor? Too much juice? Then why would a tweeter that could "take" 20 watts (is that number reasonable for a fluid-cooled driver?) fail after just a few seconds of having a 45 watt Hitachi receiver turned up to 11 (out of 10?).

Seems like your explanation of having the entire power of the receiver shift to the tweeters makes some sense. On the other hand, when someone's obviously trying to damage their speakers, it isn't just the tweeter playing.

I may just be quiet now and let you and Ken educate me.

Bret

[kkantor]

Here's a good analysis of the situation:

http://www.rane.com/pdf/note128.pdf

[Guest Bret]

Thanks for pointing there, Ken.

That explanation makes perfectly good sense. I assume it's correct by virtue of its being used to make an amplifier that won't destroy tweeters by preventing the amp's clipping.

So CLIPPING isn't causing the blown tweeters, but CLIPPING causes the COMPRESSION that sends ever-increasing amplifier output to the tweeters once the low frequencies clip.

Sooooooo. . . . amplifier clipping means destroyed tweeters, which is what we said in the first place and explains why really huge amplifiers are less likely to destroy tweeters than small ones.

But, in a scientifically specific sense, clipping doesn't destroy tweeters in much the same way that hydroplaning doesn't cause car accidents, so you were right. Right?

Bret

[soundminded]

Ken, I'll take your word for it. The last time I did a Fourier analysis was about 35 years ago. I'd have to go hunt down my old texts in the basement. Now there's a frightful thought.

[ninohernes]

This has been a very interesting thread. For the record, I have never blown anything before. I play my AR-2's loudly in my recording studio with an Adcom 125watt per channel amp, which is very clean, and I have never had any problems. The only thing that has happened, is the woofer has reached its maximum excursion, making a very loud "crack" noise, but this has only happened once. The power handling of the AR-2 is great. The woofer is great with lots of power, and since it has two tweeters, they are even more thermaly stable. (The woofer in my AR-2's have a large alnico magnet, looks just like the one in the AR-3, except a bit smaller.) I did Kens test, placing my hand over the drivers after playing loudly, and I couldent feel any heat. The big magnets do a nice job of drawing heat away.

I have also never had any trouble with my AR-3's or my 4x's. I have used my 4x's with my Adcom without any trouble, but they reside in my protable system with an Onkyo 50 watt per channel receiver, which produces clean power.

[kkantor]

Oh, it was almost a trick question. Hints:

The spectrum of the sine IS the sine. It's delivers power at (simplified) V^2/R for as long as it exists.

The step function is the integral of the delta function. The delta function has a transform of unity. So the spectrum of the step function is.... a sinc function, whose energy falls off fairly quickly with frequency.

(If you follow the above, you can see that you actually deliver more power to your tweeters if you connect then disconnect, rather short, your battery long before the cap charges up! In this manner, you approach a delta function in time, and the spectrum "whitens".)

You can take my word for it, because the sinewave will deliver vastly more power to the tweeter. The step function puts a little burst of harmonics out, like a "click," then is gone.

[kkantor]

No! .... this explains why clipped amps can cause damage when you turn them up too high. But if you suddenly substitute a large amp WITHOUT CHANGING THE INPUT, the power to the speaker does NOT go down.

Thus, a small amp does not protect speakers as well as you would think, because it compresses as it clips.

A big amp does not protect speakers, because it does not compress, but allows the desired energy to reach the speakers.

Here's the thing: if you are trying to put 200 Watts out of a 100W amp, it will clip and compress until it reaches about 200W. Thus, your "100W" speakers are "damaged by clipping."

BUT, if you attach a 200W amp to the SAME SIGNAL, it will put out 200W anyway and the speakers will blow, so attaching a larger amp does not help.

I know this is confusing, and goes against many years of urban legend. But I promise you, it is true.

[Guest Bret]

>A big amp does not protect speakers, because it does not compress, but allows the desired energy to reach the speakers. <

Ken, I don't feel confused.

"One thing was clear, when clipping occurred, tweeters blew."

The writer agrees that a clipped amplifier (for whatever reason) takes-out speakers.

"This analysis shows if a small tweeter that only handles 5

or 10 watts is used in a 100 watt speaker system it would not

blow out, even under square wave conditions. YET IT DOES. (emphasis mine) It takes a lot more than this to cause major failure. So

what’s happening?"

I understand the above paragraph to say "severe clipping is not destroying the tweeter, even though the tweeter is destroyed."

"Compression is what’s happening [3]."

I understand him to say, "It isn't the clipping, it's the compression of the signal and increased power to the tweeter that's killing the tweeter!"

"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 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."

I understand him to say once the low frequencies are clipped (which always happens first) any increases in amplitude occur in the high frequencies.

That is, once clipped, the LF doesn't become "clippier" BUT the amplifier begins putting its muscle behind the HF.

" 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)."

So, as I read it, HF amplitude equalling LF amplitude is not something that happens "in real life," and is *CAUSED* by amplifier compression which is a result of clipping. Hypothetically 100w into the tweeter is going to blow the tweeter no matter how it gets there, but it would require a 10kw amplifier to ever put 100w of "correctly proportioned" HF information into a tweeter.

So, with a speaker sytem that produces 80db @ 1w on a 30w amplifier, the speaker is going to play at about 95db before the amplifier goes into "compression". But let's say that the listener wants more and keeps rotating the volume knob. Assume a "normal" 10:1 ratio of LF to HF information in the source.

The speaker will not get louder if the amplifier is pushed harder because the amplifier isn't capable. But what will happen is that more and more HF information will make it through (being the last part of the musical spectrum to be clipped). So the spectrum goes from 10:1 (LF:HF) to 10:3 to 10:6 to 10:10 and eventually you'll get 30 watts of tweet into a 20 watt tweeter - voila! a burned-up tweeter.

But given enough power to begin with at 10:1, 20 watts wouldn't be going to the tweeter until 200w was reached.

Therefore, it is easier to put 20w through the tweeters with a 30w amplifier than a 300w amplifier. (the whole speaker system will be much louder and the amp will stay out of compression)

Now if what you are saying is that if you ask any amplifier to put 30w through the tweeter, no matter what amplifier it is, it will blow the tweeter; I agree. But if the HF/LF relationship is left intact, asking the tweeter to take 30w is going to produce a deafening volume in the entire speaker system and isn't something someone is likely to do.

So I stand by my observation - a bigger amp is going to be less likely to be driven to clipping, therefore into compression, and therefore the tweeter is less likely to be asked to absorb most of the amplifier's output.

I'm not saying that the writer is correct, Ken. But I am saying I understood the point of the paper.

Bret