Best way(s) to damage 100W speakers with a 100W/channel receiver? - AVS Forum
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post #1 of 31 Old 03-20-2013, 07:26 AM - Thread Starter
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If you have a solid AV receiver that claims "100W (20Hz - 20kHz, 0.08% THD, 2ch driven)" at 8 ohms connected to a pair of '8 ohm compatible' bookshelves with "Recommended maximum amplifier power: 100 watts", and your input source is an HTPC over HDMI, how would you go about damaging the speakers?

Just curious about the principles that come into play with that scenario, as I'm trying to determine if I'm being too conservative with my volume settings. EDIT: I've had set my limiter set to -10dB (-13dB w/ Audyssey trim) because it's loud enough in my current room and that's fine, but I don't know what the real limit is. Therefore I'm interested in staking out the performance envelope that the above power ratings suggest. Establishing a clear set of catastrophic conditions given the above criteria seems like a good place to start.
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post #2 of 31 Old 03-20-2013, 07:45 AM
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In my understanding, there are two limits that you will bump into, one is electrical, and one is mechanical. Tweeters tend to fail more due to electrical limitations, and woofers more due to mechanical. Music signal is transient in nature so speakers can typically safely playback much higher music signals than they can handle continuous sinusoidal signals. This is why speakers often speck "recommended maximum amplifier power", rather than the continuous sinusoidal signal power rating. As a practical matter, most speakers damaged electrically are due to distortion in the incoming signal. So as long as you are feeding clean power to the speaker, I would not worry about electrical damage.

Woofers have a travel limit. Exceeding this limit will cause distortion, compression, and bumping of the voicecoil against the back plate, which could permanently damage the voicecoil. Enclosure design will affect how well protected woofers are protected from such over excursion. Also, filtering out bass signals such as by setting a 60-80Hz high pass filter on the receiver will further avoid woofer damage.

As a practical matter, I would say that as long as the speakers are physically able to provide the dB output level you are looking for, and you have enough clean power to drive them, then you don't need to worry about speaker damage. Bad things happen when people try to use speakers that are too small, or an amp that's too weak.
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post #3 of 31 Old 03-20-2013, 08:28 AM - Thread Starter
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So at +18dB on the receiver dial, for a speaker that can output down to 55Hz and has two drivers:
  • could a 5000Hz sine wave be expected to burn out the tweeter? how quickly?
  • could a 60Hz sine wave be expected to burn out or physically alter the woofer? how quickly?

(^assuming a 'normal' test tone signal strength for those)

Also, would you think there is a guaranteed way to cause damage at +18dB without using test tones? (e.g. using an off the shelf movie or music source)
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post #4 of 31 Old 03-20-2013, 08:44 AM
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what is +18 relative to? My receiver wont even go to +18.

Do you have a SPL meter to verify how loud this is?

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post #5 of 31 Old 03-20-2013, 08:56 AM - Thread Starter
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Quote:
Originally Posted by afrogt View Post

what is +18 relative to? My receiver wont even go to +18.
Oh ok I thought that was a standard thing, but I guess it's just the Denon/Marantz designation for 'max' on the volume dial. It's relative to reference, although I see how that would be misleading without very sensitive speakers.
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Do you have a SPL meter to verify how loud this is?
If the JL Audio iPhone app counts, then yes.
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post #6 of 31 Old 03-20-2013, 09:05 AM
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If that is turning the volume knob all the way up on the AVR. I would not do that. It is asking for trouble. The AVR will be sending a very distorted signal at that level and could tear up your speakers and or your AVR.

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post #7 of 31 Old 03-20-2013, 09:11 AM
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Why would you want to put out a constant sine wave to a speaker just to damage it? Is there a point to this exercise?

There is no practical usefulness to know what the thermal-limited continuous power capacity of a speaker is since no actual audio program signal would approach such capacity.

If you just want to be careful with your settings, as long as you are not hearing distortion or obvious signs of driver mechanical stress, you are safe. I have a tough time watching movies at reference level. Most of the time with family, it's -30 to -20. If I am alone, I sometimes take it up to -10 or -5. Above reference level, I would worry about hearing damage.
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post #8 of 31 Old 03-20-2013, 09:16 AM
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If you really want to do damage your speakers, just bypass the receiver altogether and hook 'em right up to your main electrical power. A 60 Hertz sine wave at 110 volts is not something most speakers will deal with well.

If you want to know how to avoid damaging your speakers, never turn it up to the point where you get audible distortion. Clean sound is safe sound in virtually every case.
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post #9 of 31 Old 03-20-2013, 09:32 AM
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If you are worried about it, many (most?) AVRs have a volume limiter that you can set to prevent accidentally (animals, kids, etc) or intentionally (friends in bands) turning the volume up loud enough to damage the speakers. Setting it to like -10 should allow the AVR to play very, very loud and is likely well within the power limits of both the AVR and speakers.
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post #10 of 31 Old 03-20-2013, 09:33 AM - Thread Starter
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the OP has been edited
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Originally Posted by AV Science Sales 5 View Post

If that is turning the volume knob all the way up on the AVR. I would not do that. It is asking for trouble. The AVR will be sending a very distorted signal at that level and could tear up your speakers and or your AVR.
in this thread the goal is to damage the drivers though. This does raise the question of: what does +18dB on the dial mean in terms of wattage?
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Originally Posted by gtengineer View Post

Why would you want to put out a constant sine wave to a speaker just to damage it? Is there a point to this exercise?
I'm trying to establish a clearer 'catastrophic condition' model for myself to help understand ratings and whatnot.
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Originally Posted by JD in NJ View Post

If you really want to do damage your speakers, just bypass the receiver altogether and hook 'em right up to your main electrical power. A 60 Hertz sine wave at 110 volts is not something most speakers will deal with well.
that's cheating smile.gif
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Originally Posted by JD in NJ View Post

If you want to know how to avoid damaging your speakers, never turn it up to the point where you get audible distortion. Clean sound is safe sound in virtually every case.
this is not a complete answer for me; in fact that answer is exactly why I put up the thread
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Originally Posted by dmsdms View Post

If you are worried about it, many (most?) AVRs have a volume limiter that you can set to prevent accidentally (animals, kids, etc) or intentionally (friends in bands) turning the volume up loud enough to damage the speakers. Setting it to like -10 should allow the AVR to play very, very loud and is likely well within the power limits of both the AVR and speakers.
lol that's how I've had it set, and it gets plenty loud at -10, but it's not the extreme answer I'm after here. I'm trying
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post #11 of 31 Old 03-20-2013, 10:12 AM
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Originally Posted by Resonate View Post

how would you go about damaging the speakers?
By playing too loud. When you do you'll hear distortion, which may be sourced in the amp, or the speakers, or both. If you're prudent you'll turn it down before damage occurs. If not you'll be back here asking what to buy next.

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post #12 of 31 Old 03-20-2013, 10:39 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

By playing too loud. When you do you'll hear distortion, which may be sourced in the amp, or the speakers, or both. If you're prudent you'll turn it down before damage occurs. If not you'll be back here asking what to buy next.
I was hoping you'd have an (or the) answer.
If I may:
  • What good are the ratings? On paper, it seems like the receiver should have no problem delivering clean wattage up to its channel rating, which is also the rated speaker limit.
  • So basically anything that distorts is likely(?) to cause damage after some period of time, and the only way to divine the limit is to hit distortion and then back off?
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post #13 of 31 Old 03-20-2013, 12:51 PM
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Quote:
Originally Posted by Resonate View Post

I was hoping you'd have an (or the) answer.
If I may:
  • What good are the ratings? On paper, it seems like the receiver should have no problem delivering clean wattage up to its channel rating, which is also the rated speaker limit.
True. What isn't on paper is how much it will deliver when pushed into clipping/high distortion. That can easily be 6dB/ 4x the rated power long term, and 10dB/10x the rated power short term.
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[*] So basically anything that distorts is likely(?) to cause damage after some period of time, and the only way to divine the limit is to hit distortion and then back off?
Yes. If the speakers are distorting that will lead to long term heat damage and failure. If the amp is clipping it will create a far higher than normal power density in the higher harmonics, and that will over-power tweeters, causing them to fail, even if the speaker's nominal power rating isn't exceeded.

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post #14 of 31 Old 03-20-2013, 01:19 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

True. What isn't on paper is how much it will deliver when pushed into clipping/high distortion. That can easily be 6dB/ 4x the rated power long term, and 10dB/10x the rated power short term.
Yes. If the speakers are distorting that will lead to long term heat damage and failure. If the amp is clipping it will create a far higher than normal power density in the higher harmonics, and that will over-power tweeters, causing them to fail, even if the speaker's nominal power rating isn't exceeded.

Thanks that's more what I was after. I'd come across an isolated article about those big dynamic swings but it had almost seemed like hyperbole. Many questions arise, but I'll limit to these:
  • Does the distortion have to be VERY obvious to be potentially damaging?
  • Is dynamic compression a type of potentially damaging distortion?
  • Is the receiver ever in danger of anything beyond automatic thermal shutdown?

Also thanks to gtengineer
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post #15 of 31 Old 03-20-2013, 02:04 PM
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Quote:
Originally Posted by Resonate View Post

[*] Does the distortion have to be VERY obvious to be potentially damaging?
Usually, but some speakers aren't as damage resistant as others.
Quote:
[*] Is dynamic compression a type of potentially damaging distortion?
It can be if you overdo it, but when you overcompress you hear it as a pumping sound that's not pretty, so you're not likely to do so.
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[*] Is the receiver ever in danger of anything beyond automatic thermal shutdown?
Probably not.

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post #16 of 31 Old 03-20-2013, 05:55 PM
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Quote:
Originally Posted by Resonate View Post

Thanks that's more what I was after. I'd come across an isolated article about those big dynamic swings but it had almost seemed like hyperbole. Many questions arise, but I'll limit to these:
  • Does the distortion have to be VERY obvious to be potentially damaging?
  • Is dynamic compression a type of potentially damaging distortion?
  • Is the receiver ever in danger of anything beyond automatic thermal shutdown?

Also thanks to gtengineer

It seems like you're considering pushing your speakers to the limits. What speakers are these anyway? And which receiver do you have?
Quote:
If I may:
What good are the ratings? On paper, it seems like the receiver should have no problem delivering clean wattage up to its channel rating, which is also the rated speaker limit.

When these amps/receivers are spec'd you don't know how long they can sustain the rated power. They may have been rated for 100 watts/channel for a very short period of time so if you plan to push your speakers for an extended period you'll probably get clipping and distortion, which will damage your speakers.

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post #17 of 31 Old 03-20-2013, 06:52 PM - Thread Starter
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Quote:
Originally Posted by afrogt View Post

It seems like you're considering pushing your speakers to the limits. What speakers are these anyway? And which receiver do you have?
yeah I thought it might sound that way so I edited the OP earlier:
Quote:
I've had set my limiter set to -10dB (-13dB w/ Audyssey trim) because it's loud enough in my current room and that's fine, but I don't know what the real limit is. Therefore I'm interested in staking out the performance envelope that the above power ratings suggest. Establishing a clear set of catastrophic conditions given the above criteria seems like a good place to start.
I'm running Cambridge Audio S30s and a Marantz SR5007
Basically, when I think about recommending the S30s (e.g. to my mom for HT, say) I'm not sure how they'll fare in a bigger room, with positions as far back as 20', and so I wanted to get a sense of the limits described by ratings without testing [and possibly damaging] anything.
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Originally Posted by afrogt View Post

When these amps/receivers are spec'd you don't know how long they can sustain the rated power. They may have been rated for 100 watts/channel for a very short period of time so if you plan to push your speakers for an extended period you'll probably get clipping and distortion, which will damage your speakers.
The power supply on the Marantz is beefier than most (650w consumption), so I was guessing the S30s would hit some kind of wall well before the amp decided to clip, but I don't know how the receiver is rated and given the crazy voltage swings at loud volumes, nor do I know how the S30s are rated. Fwiw Andrew Jones described the intense Pioneer gen2 power rating process in detail somewhere (can't find it now), but I dunno how standard that practice is across manufacturers. It involved measuring the speakers, then running a "shaped sound" through them for like an hour at the power limit they were shooting for, and then measuring the speakers again. Any difference in the measurements, and they failed that rating, and the design was tweaked.

After Bill's comments, it sounds like there's no real way for the end user to tell where 'the line' is without hands on testing using some representative source material; and I get the impression that it's ok to bounce off the distortion threshold to find out where it is.
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post #18 of 31 Old 03-21-2013, 07:04 AM - Thread Starter
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Here's that dynamics article I was talking about: Soft to Loud: The Nature of Power and Dynamic Headroom. I think when I initially read it I saw how it was talking a lot about reference level dB scenarios and citing his company's high end speakers in examples, so I didn't know how applicable it was to lower dB situations. Now it makes more sense. An interesting excerpt:
Quote:
"The problem with many amplifiers and A/V receivers designed for economy (the most watts for the dollar) is that they make the transformer just big enough to produce the voltage output they need [to meet sustained power output measurements into an 8-ohm load], and just big enough capacitors to supply the sustained, continuous voltage and current they need for continuous power, and then the amplifiers quit, so those amplifiers have no real headroom. On top of this, the power may be calculated to be the rated output for one channel at full power and the other five at 1/8 power. So a 100-watt six-channel A/V receiver actually only has 162.5 watts of total power or 27 watts per channel with all channels driven. The better amp builders, who design for performance (reproductive accuracy for the dollar) rather than economy, will install these big transformers with huge capacitors, so then they have all these joules of energy in reserve to produce the dynamics necessary for the music."
Another important factor in dynamic headroom is that the output transistors must be very tough, and there have to be enough of them, to handle these instantaneous high-current conditions, because a great deal of heat is generated very quickly. If the transistors aren't of sufficient quality, they'll be pushed outside of the "SOA" (safe operating area) and fail. And that may happen because there isn't enough heat-sinking to keep the output devices cool under these very dynamic conditions.
One hugely important factor we've ignored so far in this discussion is whether the speakers (and the individual drivers) receiving these 200-watt or 400-watt instantaneous bursts of power from an amplifier capable of 3 dB or more of dynamic headroom can handle the peaks without significant distortion. We already know that the M80ti's are tested up to 1,200 watts of input power, but many speakers when confronted with spikes of power input may suffer something called "dynamic compression."
and
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We've become accustomed to accepting some distortion with our reproduced music, because all amplifier's distortion ratings gradually increase as they approach their output limits or slightly clip the audio signals. When that happens, we turn down the volume because distortion starts to intrude on our listening pleasure, and it sounds "too loud."
This seems to explain why Andrew Robinson was hooking up crazy pro amplifiers to the Tekton Pendragons during testing, despite their being very sensitive speakers:
Quote:
I ran two Crown XLS 2000 amplifiers in bridged mono mode to each Pendragon, feeding them a staggering 1,300 watts apiece.
I was going to ask if there were such a thing as an amplifier that didn't output any meaningful distortion at its max output level, but I'm guessing the answer is no, and that the solution is just to get an amplifier that seems extremely overpowered and only turn it up a little.
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post #19 of 31 Old 03-21-2013, 08:43 AM
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Quote:
Originally Posted by Resonate View Post

I was going to ask if there were such a thing as an amplifier that didn't output any meaningful distortion at its max output level, but I'm guessing the answer is no, and that the solution is just to get an amplifier that seems extremely overpowered and only turn it up a little.
The answer is no because most amps aren't measured at full power, they're measured at a certain distortion level. Some pro amps are measured at full power, and they'll state the THD at that output, as well as output at a low THD.

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post #20 of 31 Old 03-21-2013, 08:56 AM
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Quote:
Originally Posted by Resonate View Post

If you have a solid AV receiver that claims "100W (20Hz - 20kHz, 0.08% THD, 2ch driven)" at 8 ohms connected to a pair of '8 ohm compatible' bookshelves with "Recommended maximum amplifier power: 100 watts", and your input source is an HTPC over HDMI, how would you go about damaging the speakers?

Find a source such as a CD I burned that had 15 KHz tones and play it just below clipping on the AVR. I would expect the tweeters to be fried in a few minutes.
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post #21 of 31 Old 03-21-2013, 09:01 AM
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Quote:
Originally Posted by Resonate View Post

[*] Does the distortion have to be VERY obvious to be potentially damaging?

Depends.

I can think of ways to distort a signal to make a maximumally damaging signal out of it, but some signals don't make good ingredients for these recipies. One of the tricky ways to make signals that don't sound obviously distorted is to use a pure tone at a very high frequency where the ear is pretty insensitive. The distortion is at some frequency even higher than my test tone, so it can't be heard at all!
Quote:
[*] Is dynamic compression a type of potentially damaging distortion?

Depends on how much dynamic compression of what kind. Much dynamic compression is due to the resistance of voice coils increasing when they warm up. So now the question is how much warming, enough to permanently damage the drivers or not?
Quote:
[*] Is the receiver ever in danger of anything beyond automatic thermal shutdown?

Depends. I have destroyed an AVR on the test bench by bringing its output up to just below clipping at a high frequency and leaving it running for like an hour. There was a protective thermal fuse inside the power transformer, and it fried.

The good news was that it was old and cheap, so whatever.
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post #22 of 31 Old 03-21-2013, 09:24 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

The answer is no because most amps aren't measured at full power, they're measured at a certain distortion level. Some pro amps are measured at full power, and they'll state the THD at that output, as well as output at a low THD.
Gotcha.
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Originally Posted by arnyk View Post

Find a source such as a CD I burned that had 15 KHz tones and play it just below clipping on the AVR. I would expect the tweeters to be fried in a few minutes.
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Originally Posted by arnyk View Post

I have destroyed an AVR on the test bench by bringing its output up to just below clipping at a high frequency and leaving it running for like an hour. There was a protective thermal fuse inside the power transformer, and it fried. The good news was that it was old and cheap, so whatever.
nice, and interesting to hear some times
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One of the tricky ways to make signals that don't sound obviously distorted is to use a pure tone at a very high frequency where the ear is pretty insensitive. The distortion is at some frequency even higher than my test tone, so it can't be heard at all!
*gulp*

This article from 10 Things about Audio Amplifiers You've Always Wanted to Know on Audioholics (also authored by Alan Lofft), makes the effect of a [badly] clipped signal a little clearer for me:
Quote:
How Do Small, Low-Powered Amplifiers Put Speakers at Risk?
Initially, it seems contradictory—how could a low-powered amplifier burn out speakers, when amplifiers of 200 or 400 watts per channel would seem to put speakers at much greater risk? The reason is that a small amplifier of 10 or 20 watts per channel can easily be driven into distortion and “clipping” with even moderately loud playback and dynamic peaks in loudness. The clipping cuts off the waveform and turns the output signal into an almost pure constant DC signal, which can quickly cause the fine wires in the speaker’s voice coils to overheat and melt. A large amplifier outputs clean power to the speakers –distortion-free AC audio signals—that the speaker voice coils will accept on a momentary basis without damage.

Special thanks to Axiom Audio for allowing us to reprint this article.
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post #23 of 31 Old 03-21-2013, 10:20 AM - Thread Starter
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I found the Pioneer testing protocol I was talking about; turns out it was in the Audioholics review:
Quote:
Editorial Note on Pioneer Power Testing by Andrew Jones

If we rate power handling at max 100w, what we do for testing is run the speaker with shaped noise at 1/3 full power, so in this example 33W average power for 96 hours. This is a lot of power!

After 96 hours, we let it cool down. It must pass all measurements with no change. Then we test for 24 hours at 1/2 power (50W), it must not fail, and must pass most of the specs with only a little change.

Then we test at 100W. If it fails, it must do so safely!

In addition, we have particular music selections that are bass torture tests. These are well in excess of the standard testing.
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post #24 of 31 Old 03-21-2013, 02:30 PM
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Be careful of what you see on the internet, because this is totally false:
Quote:
The clipping cuts off the waveform and turns the output signal into an almost pure constant DC signal, which can quickly cause the fine wires in the speaker’s voice coils to overheat and melt. A large amplifier outputs clean power to the speakers –distortion-free AC audio signals—that the speaker voice coils will accept on a momentary basis without damage. Special thanks to Axiom Audio for allowing us to reprint this article.

It's hard to believe a speaker manufacturer would publish that drivel, but frankly the more I learn about Axiom Audio the less impressed I am with their level of engineering expertise. For advise about clipping you can take to the bank this is from an irrefutable source:

http://forum.qscaudio.com/forum/viewtopic.php?f=29&t=2736

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post #25 of 31 Old 03-21-2013, 03:02 PM
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^Yeah, wow, another FAIL for Axiom.

For every new thing I learn, I forget two things I used to know.
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post #26 of 31 Old 03-21-2013, 03:39 PM
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The author is not an audio engineer...

TAM
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post #27 of 31 Old 03-21-2013, 04:17 PM
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Originally Posted by ex-labdriver View Post

The author is not an audio engineer...

TAM

Do you work for Axiom?
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post #28 of 31 Old 03-21-2013, 04:36 PM
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Originally Posted by ex-labdriver View Post

The author is not an audio engineer...

TAM

Alan Loft is an Axiom Resident "Expert". He isn't and engineer but he's been around for 40 some years in the A/V industry.
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post #29 of 31 Old 03-21-2013, 05:18 PM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

For advise about clipping you can take to the bank this is from an irrefutable source:http://forum.qscaudio.com/forum/viewtopic.php?f=29&t=2736
very neat, thanks - that whole Amplifier FAQ section is a good read
Quote:
A general rule of thumb for choosing a suitable amount of amp power is to match the amplifier’s power rating to the loudspeaker’s program power rating. It doesn’t have to be an exact match—within about ±20% is fine. For example, if you have two 8Ω loudspeakers with a program power rating of 350 watts, then you could look for a two-channel amp rated at around 280 to 420 watts per channel into 8 ohms...The idea is that if you choose your amp this way and avoid driving it into significant clipping, your loudspeaker will be fairly safe from blowing out due to overpowering. If the loudspeaker has no program power rating, then use about 1.5 to 2× its continuous (often called “RMS”) power rating as a target.
Does "program power rating" equate to "Recommended maximum amplifier power: 100 watts"?
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post #30 of 31 Old 03-21-2013, 05:25 PM
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Nope, just a long time - 20+ years - satisfied customer.

As far as the article, most of it is beyond me. The experts at AH must have vetted it & thought that it had some merit to publish it on their website where it has remained up for a couple of years.

Being a layman, I don't pretend to know what happens electrically & mechanically during clipping; however, I do know that it is not good for your gear & it is best to avoid it at all costs. If you drive your equipment into clipping, eventually something is going to break, most likely sooner rather than later, & it probably isn't good for your hearing either...

TAM
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