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post #1 of 33 Old 08-08-2013, 02:51 AM - Thread Starter
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Hi I listen to music on wharfedale diamond 9.6 (giant 4 way with 2 8" woofers rated 6ohm 90db sens) on a denon avr 789.

It rates 90w 2 chan 20-20khz 0.05% thd 8 ohm and 110w 20-20khz 0.7%thd 6 ohm.

These are my questions

1) is 0.7% thd mean clipping at that wattage?

2) will a denon 4308 make any difference if what I read is 3db need doubling of wattage if it rates 140w for the same thds? Or are its circuitry better hence I get better sound inspite of the aforementioned laws of physics?

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post #2 of 33 Old 08-08-2013, 03:50 AM
 
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Quote:
Originally Posted by joker97 View Post

Hi I listen to music on wharfedale diamond 9.6 (giant 4 way with 2 8" woofers rated 6ohm 90db sens) on a denon avr 789.

It rates 90w 2 chan 20-20khz 0.05% thd 8 ohm and 110w 20-20khz 0.7%thd 6 ohm.

These are my questions

1) is 0.7% thd mean clipping at that wattage?

Yes,0.7% THD it probably indicates that there is a little clipping. A good average SS power amp will have somewhere between 0.01 and 0.05% THD just before clipping. Manufacture's routinely give power ratings that imply the amp is clipping a little.
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2) will a denon 4308 make any difference if what I read is 3db need doubling of wattage if it rates 140w for the same thds? Or are its circuitry better hence I get better sound inspite of the aforementioned laws of physics?

It takes 10 dB more output (coincidentally 10 times more power) when power is the limitation in a system, to create the perception of "Twice as loud". Thing is, unless you are clipping your amplifier in normal use, the extra power is useless.

BTW music power is probably a more reliable predictor of when a amplifier will clip in your system, then RMS power due to the dynamic nature of the music we actually listen to.
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post #3 of 33 Old 08-08-2013, 12:46 PM
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Quote:
Originally Posted by arnyk@pcavtech View Post

Yes,0.7% THD it probably indicates that there is a little clipping. A good average SS power amp will have somewhere between 0.01 and 0.05% THD just before clipping. Manufacture's routinely give power ratings that imply the amp is clipping a little.
It takes 10 dB more output (coincidentally 10 times more power) when power is the limitation in a system, to create the perception of "Twice as loud". Thing is, unless you are clipping your amplifier in normal use, the extra power is useless.

BTW music power is probably a more reliable predictor of when a amplifier will clip in your system, then RMS power due to the dynamic nature of the music we actually listen to.

Arny, when I look at amp output tests, I see a more or less gradual rise in THD plus noise up to some knee where THD+N rises significantly faster with added power. I never see the knee identified as "clipping.' It's always 1% or some fraction of one percent (for home sound reproduction purposes) and the slope of the THD+N curve is typically identical before and after that point.

IOW< to me "clipping"is a more or less arbitrary point on a curve, not any real change in the amp's function "at the clipping point."
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post #4 of 33 Old 08-08-2013, 01:42 PM
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Clipping is nothing more than the speaker trying to draw more current than the final stage of the amplifier can deliver. It results in distortion - lots of it. It isn't gradual at all. It is like falling off a cliff. Now distortion can rise with current draw and that can be a gradual thing but there is nothing gradual about reaching the clipping point.
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post #5 of 33 Old 08-08-2013, 02:02 PM - Thread Starter
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Thanks

So is it worth me flying 1000 miles to get the denon 4308 upgrade?

Also if my speaker sens is 90db per watt at 1m at 1khz that totally means nothing when a rock band is playing at the entire spectrum or is it pretty good indicator?

Also ... (* opening thecan ofworms) Can anyone tell me whether I need to get a poweramp? (My denon 789 has no preamp outs)

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post #6 of 33 Old 08-08-2013, 02:23 PM
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Originally Posted by FMW View Post

Clipping is nothing more than the speaker trying to draw more current than the final stage of the amplifier can deliver.

Nope.

Amplifiers for conventional speakers are simple voltage multipliers.

You put 0.1V in, you get 2V out.
You put 1.0V in, you get 20V out.

Given 30V output stage power supply rails putting 2V in cannot produce 40V out but the amplifier will try, outputting 30V less a few diode drops until the input signal drops below 1.5V and the input to output ratio is possible again.

That's clipping.
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post #7 of 33 Old 08-08-2013, 06:03 PM - Thread Starter
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So will thedenon 4308 be a worthwhile upgrade? Still not sure

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post #8 of 33 Old 08-08-2013, 06:26 PM
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Quote:
So will thedenon 4308 be a worthwhile upgrade? Still not sure
In general, upgrading an AVR for more power rarely makes sense. Newer AVRs may have features you want, however.

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post #9 of 33 Old 08-08-2013, 07:45 PM
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Use this calculator to get an idea of how much power you may need...

http://www.allegrosound.com/Power_AllegroSound.html

It is a ratio of speaker sensitivity vs your distance from the speakers vs how loud you want to push them.
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post #10 of 33 Old 08-08-2013, 09:24 PM - Thread Starter
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Thanks it came up to 95w

Not sure what it means if my amp is rated for 90w at 8ohm and my speakers are rate d 6ohm.

What I don't understand ... speakers say 40w-200w - surely you can feed it 1w playing quietly?

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post #11 of 33 Old 08-08-2013, 10:11 PM
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Quote:
Originally Posted by joker97 View Post

Not sure what it means if my amp is rated for 90w at 8ohm and my speakers are rate d 6ohm.

Then you would probably be getting around 120w. Though you would need to find out if that is its rating for '2 channel driven'.

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What I don't understand ... speakers say 40w-200w - surely you can feed it 1w playing quietly?

Absolutely. They're just recommending an amplifier that is rated between 40 to 200w.
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post #12 of 33 Old 08-09-2013, 05:11 AM
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Quote:
Originally Posted by JHAz View Post

Quote:
Originally Posted by arnyk@pcavtech View Post

Yes,0.7% THD it probably indicates that there is a little clipping. A good average SS power amp will have somewhere between 0.01 and 0.05% THD just before clipping. Manufacture's routinely give power ratings that imply the amp is clipping a little.
It takes 10 dB more output (coincidentally 10 times more power) when power is the limitation in a system, to create the perception of "Twice as loud". Thing is, unless you are clipping your amplifier in normal use, the extra power is useless.

BTW music power is probably a more reliable predictor of when a amplifier will clip in your system, then RMS power due to the dynamic nature of the music we actually listen to.

Arny, when I look at amp output tests, I see a more or less gradual rise in THD plus noise up to some knee where THD+N rises significantly faster with added power. I never see the knee identified as "clipping.'

It may not be labelled that way, but that is what it is. If you do bench tests with pure sine waves, at THD analyzer will present the symptoms of clipping at that point.
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It's always 1% or some fraction of one percent (for home sound reproduction purposes) and the slope of the THD+N curve is typically identical before and after that point.

That's all characteristic of ideal clipping.
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IOW< to me "clipping"is a more or less arbitrary point on a curve, not any real change in the amp's function "at the clipping point."

The amp's function and operation does change internally at the point where clipping sets in. For example the output devices typically enter a different mode of operation called "saturation" during the time where the output is clipped. The fact that modern amps do this in such a clean way is the result of years of refinement.
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post #13 of 33 Old 08-09-2013, 05:13 AM
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Quote:
Originally Posted by FMW View Post

Clipping is nothing more than the speaker trying to draw more current than the final stage of the amplifier can deliver. It results in distortion - lots of it. It isn't gradual at all. It is like falling off a cliff. Now distortion can rise with current draw and that can be a gradual thing but there is nothing gradual about reaching the clipping point.

Actually, most clipping is about voltage, not current. Its nothing more than trying to get more volts out of a power amp than it has power supply voltage to support.

Clipping due to internal current limiting is possible if the load impedance is too low, but far less frequently observed.
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post #14 of 33 Old 08-09-2013, 05:26 AM
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Originally Posted by joker97 View Post

Thanks it came up to 95w

Not sure what it means if my amp is rated for 90w at 8ohm and my speakers are rate d 6ohm.

What I don't understand ... speakers say 40w-200w - surely you can feed it 1w playing quietly?

Back when I had a 2 channel power amp with LED power meters, 1 watt was quite loud.

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post #15 of 33 Old 08-09-2013, 06:21 AM
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Quote:
Originally Posted by JHAz View Post

Arny, when I look at amp output tests, I see a more or less gradual rise in THD plus noise up to some knee where THD+N rises significantly faster with added power. I never see the knee identified as "clipping.' It's always 1% or some fraction of one percent (for home sound reproduction purposes) and the slope of the THD+N curve is typically identical before and after that point.
I've measured a lot of SS amps over the years. With very few exceptions, they all have a quite well defined knee where the distortion increases rapidly. Anything beyond that knee is clipping and the number (%) is fairly irrelevant as the amp has exceeded it clean power values, ie hit a voltage rail and changed the signal waveshape significantly and added an amount of THD because of it. Manufacturers may choose a number that makes their amp look more powerful to give a (hopefully) better chance of sales in a competetive market.

Here is a fairly typical sample of a convention class AB amp, a Bryston 7B.



EDIT: added a couple of sentences this morning for clarity.
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post #16 of 33 Old 08-09-2013, 12:56 PM - Thread Starter
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So can the 4308 give me more voltage?

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post #17 of 33 Old 08-09-2013, 01:37 PM
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So can the 4308 give me more voltage?
Why do you even care?

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post #18 of 33 Old 08-09-2013, 05:49 PM
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Originally Posted by A9X-308 View Post

I've measured a lot of SS amps over the years. With very few exceptions, they all have a quite well defined knee where the distortion increases rapidly. Anything beyond that knee is clipping and the number (%) is fairly irrelevant as the amp has exceeded it clean power values, ie hit a voltage rail and changed the signal waveshape significantly and added an amount of THD because of it. Manufacturers may choose a number that makes their amp look more powerful to give a (hopefully) better chance of sales in a competetive market.

Here is a fairly typical sample of a convention class AB amp, a Bryston 7B.




EDIT: added a couple of sentences this morning for clarity.


The graph is consistent with my description.

Here's what John Atkinson says about that specific measurment" "The Bryston's maximum power delivery is specified at 600W into 8 ohms (27.8dBW); the traces in fig.3 indicate that at clipping (defined as 1% THD+N), the amplifier puts out 632W into 8 ohms (28dBW), 930W into 4 ohms (26.7dBW), but 690W into 2 ohms (22.4dBW).

"at clipping (defined as 1% THD+N)" is what he usually says (some tube amps get 3%). I've never seen the knee described as the point of clipping.
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post #19 of 33 Old 08-09-2013, 05:56 PM
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The 4308 will not provide an audibly louder sound. Look at the features and decide if they are worth it to you.

Aside: I think the IHF defined clipping at 1% THD back in the 70's or 80's when I got my license, but that was a while back so I could be wrong. In any event, I have seen manufacturers range between 1% and 10% to define "clipping". It is not a black-and-white thing. The knee's sharpness varies with amp design, load impedance, and usually with frequency (loop gain and all that jazz).

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post #20 of 33 Old 08-10-2013, 03:57 AM - Thread Starter
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4308 won't provide extra headroom prior to clipping?

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post #21 of 33 Old 08-10-2013, 07:27 AM
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Yes, it has higher output. The question is whether the extra headroom is worth it to you. You need to decide that for yourself.

3 dB is only a slight increase in volume and requires twice the power. Doubling the loudness (in the midrange) requires about 10 dB, ten times the power. Chances are you are only using a few watts at your average listening levels. Going from 90 W to 140 W is a 1.92 dB increase.

If you want a 4308 for the new features and improvements in room correction, additional formats it handles etc. that is fine. If you want it solely to play louder it may not be a cost-effective move.

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post #22 of 33 Old 08-10-2013, 07:36 AM
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Quote:
Originally Posted by joker97 View Post

So can the 4308 give me more voltage?

One thing to remember how much power it takes to actually make a system louder, and that only is meaningful if you are out of power.

Those of us who have Audyssey and have set our systems up with it know the clipping point of our equipment with digital inputs. Just set your system up to play a muted or paused source, and turn the volume control all the way up and read the digital level on your AVR's front panel. If it is 85.5 dB or more, then that means you can reach reference levels without clipping. Anything over 85 dB is pure headroom and your system can get darn loud without clipping.

It takes 10 dB to give the impression of "twice as loud" and that is 10 times more power. Your typical upgrade power amp with 200 wpc is only about 3 dB louder. Listen to your system while you vary its volume knob by 3 dB. Tain't much and what would you pay for that?
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post #23 of 33 Old 08-10-2013, 07:38 AM
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4308 won't provide extra headroom prior to clipping?
Yes, but if your current AVR isn't clipping, that extra headroom will provide you no benefit at all. And I doubt your current system has a clipping problem.

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post #24 of 33 Old 08-10-2013, 07:41 AM
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Originally Posted by JHAz View Post


"at clipping (defined as 1% THD+N)" is what he usually says (some tube amps get 3%). I've never seen the knee described as the point of clipping.

That's because I hadn't yet shared this factoid with AVS, I guess. ;-)

It's true.

If you know how clipping comes to be and what it looks like on test equipment, the knee is indeed the point where clipping starts.

I remember testing some QSC power amps (which many love to hate). It turned out that the clipping indicate glowed pretty brightly at 0.02% THD on the distortion meter. I looked at the output wave on a scope and there was indeed some flat topping.

I probed the inside of the amp and found that indeed the output devices were saturating, and Vout was very close to VCC. That's clipping by the book!

Clipping is generally well-defined. A bunch of things happen internally and externally at the same time.

Every other amp I've ever tested from Brooks to Threshold works the same way, as did all the amps I designed from scratch. Amps vary slightly in terms of how sharp the knee is and how steeply distortion goes up past the knee. They also vary in terms of how the approach to the knee looks. That Bryston mentioned above looks a little dirty before the knee, but given how far down any artifacts are, its just not a problem.
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post #25 of 33 Old 08-10-2013, 07:47 AM
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You would be amazed at how high the THD has to get in many cases depending on the content for clipping to become audible. It's MUCH higher than most people with typical speakers would believe.
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post #26 of 33 Old 08-10-2013, 07:55 AM
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Originally Posted by DaveMcLain View Post

You would be amazed at how high the THD has to get in many cases depending on the content for clipping to become audible. It's MUCH higher than most people with typical speakers would believe.

One big problem is how much distortion speakers have. The other situation is how the ear works. Mediocre speakers have distortion down maybe 30 dB, but worse within an octiave of their bass roll off. Good speakers have distortion about 40 dB down (1%) and the best don't get much better than 60 dB down (0.1%).

Manufacturers rate power at anywhere from 0.02% to 10% THD. 10% THD is barely audible to pretty audible depending on how the harmonics are distributed and the nature of the music. High order distortion tends to be more audible because the artifacts are more likely to pile up where the ear is more sensitive. Any distortion that is 60 dB down or more will be very, very challenging to hear even under ideal conditions. A lot of middle of the road electronics has distortion that is 80 or more dB down.

The important thing to remember is that manufacturer ratings are marketing choices. Designers have a lot of choices they can make to have a certain amount of distortion at a certain power level with a certain load. Its pretty much controlled by the number of turns on the secondary of the amp's power transformer. That's the fine tuning control. You add or subtract or choose different output devices to make the amp reliable.
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post #27 of 33 Old 08-10-2013, 07:56 AM
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You would be amazed at how high the THD has to get in many cases depending on the content for clipping to become audible. It's MUCH higher than most people with typical speakers would believe.
I read once (and I can't remember the source) that a system has to be clipping 1% of the time before it's audible. You aren't going to notice the occasional clipped transient peak.

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post #28 of 33 Old 08-10-2013, 09:13 AM
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Originally Posted by mcnarus View Post

Quote:
You would be amazed at how high the THD has to get in many cases depending on the content for clipping to become audible. It's MUCH higher than most people with typical speakers would believe.

I read once (and I can't remember the source) that a system has to be clipping 1% of the time before it's audible.

I know how to set up a musical recording where 0.1% THD is clearly audible. Below that, its pretty hard to hear.

You aren't going to notice the occasional clipped transient peak.[/quote]

That's true. Nobody is going to notice a few milliseconds of horrific clipping (50%) here, a few milliseconds there
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post #29 of 33 Old 08-10-2013, 03:02 PM
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Quote:
Originally Posted by JHAz View Post

Here's what John Atkinson says about that specific measurment" "The Bryston's maximum power delivery is specified at 600W into 8 ohms (27.8dBW); the traces in fig.3 indicate that at clipping (defined as 1% THD+N), the amplifier puts out 632W into 8 ohms (28dBW).
The SST brochure gives rated spec as 0.005% at 600W/8R and it goes from this to 1% at 632W/8R a 46dB difference in 0.2dBW (an inaudible difference with programme material) and you don't consider that a 'knee'? I already said in the previous post that clipping is the point where the waveshape changes because of an amp limitation and distortion increases; the 1% number is just a uniform metric so that different amps can be compared on the same level. It could easily be another number, say 0.1%.
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Originally Posted by JHAz View Post

"at clipping (defined as 1% THD+N)" is what he usually says (some tube amps get 3%). I've never seen the knee described as the point of clipping.
Because you haven't seen it described that way, those of us involved in amp design most likely have.

Tube amps get away with a 3% or 5% number because if they didn't use that (sometimes not specified at all) they'd never be able to compete in the marketplace with SS amps as thier power outputs would be much lower in many cases that what manufacturers currently specify. Depending upon topology, especially those with little to no gNFB have a slowly changing spectrum, typically with no obvious 'knee' so you need to pick a number (and parameters) and go with that. An OTTOMH example is the Cary 805. Contrast with the ARC Ref 150.
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post #30 of 33 Old 08-10-2013, 05:04 PM
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Originally Posted by A9X-308 View Post

The SST brochure gives rated spec as 0.005% at 600W/8R and it goes from this to 1% at 632W/8R a 46dB difference in 0.2dBW (an inaudible difference with programme material) and you don't consider that a 'knee'? I already said in the previous post that clipping is the point where the waveshape changes because of an amp limitation and distortion increases; the 1% number is just a uniform metric so that different amps can be compared on the same level. It could easily be another number, say 0.1%.
Because you haven't seen it described that way, those of us involved in amp design most likely have.

Tube amps get away with a 3% or 5% number because if they didn't use that (sometimes not specified at all) they'd never be able to compete in the marketplace with SS amps as thier power outputs would be much lower in many cases that what manufacturers currently specify. Depending upon topology, especially those with little to no gNFB have a slowly changing spectrum, typically with no obvious 'knee' so you need to pick a number (and parameters) and go with that. An OTTOMH example is the Cary 805. Contrast with the ARC Ref 150.

No, despite the fact that one percent is laughably close, in meaningful output, to the knee, it is NOT the knee. Weirds me out when folks who seem all science like start saying "but look, it's close enough." when I said they were the same, I meant they were effectively the same for purposes of my testimony." Where I dwell, when stuff like that comes up one to three lawyers are just hoping the testimony will get to the end of the day so they can figure out how to rehabilitate their perfectly truthful and scientific witness that the jury has been convinced lied to them. So yeah, forty or 60 or whatever watts above the knee is not relevant in SPL at the listening position at the powers we are looking at, but it's still 40 or 60 watts . . . or whatever

Part of the issue for me is the bizarre discussions that arise around "clipping" and damage to speakers. At the knee, or even at 1%, absent a really weird spectrum for the distortion, we can call it "clipping' but it's meaningless with respect to "excess" power delivered to any driver . . . . But folks act like if you can call it clipping, it is outputting a square wave. It ain't by miles (as is obvious both in the chart you posted, and I'm sure every amp test you ever conducted). I'll reiterate my old saw, apparently guitar players identify amps at ten percent distortion as being "clean." You can't even reasonably estimate power at 10 percent distortion from the graphs in Stereophile, at least usually. ANd you're still quite far from outputting a square wave. . . . but I digress.

It does seem like if there was a supersecret engineers' cabal agreement that everybody will think of the knee as the onset of clipping but dwill ensure that it is never discussed that way in any technical journal or specification, and to make sure that the uninitiated don't find out . . . . I want to know. And somebody would tell..
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