Double Blind tests *did* show amplifiers to sound different

[Bloomer]

Bats make a clicking sound when they fly around looking for bugs.

Have any of these studies shown positive results when repeated? Or reproduced? Reproducibility is really tough with human subjects. Without at least, repeatability, any experiment that can have more than one outcome, luck can't be separated from a true result. I've never seen (maybe they exist) any sort of binomial or whatever distribution reported. Who are the subjects for these tests? Lots of fairly uncontrollable variables here.

Then there's the fact that hearing changes easily and significantly from external and physiological variations we experience all the time.

Ever get into your car after work, start it and the radio is waaay to loud when it was A-OK when you adjusted it in the morning?

Finally, does any of this matter? You're going to buy what you want. If perceptions could be measured accurately, what do we do with the information?

 

[SIY]

I've never seen (maybe they exist) any sort of binomial or whatever distribution reported.

Tell us you've never read the literature without telling us you've never read the literature.

 

[Philbo King]

Sure . The amp was driven with a pure sine wave into a resistive "dummy" load. Then the volume was turned up until a lot of distortion occurred. What the graphs show is that the typical picture we have in mind of a pretty clean, clipped flat top is not what happens. Instead we get very odd shapes.

The odd shape occurs because when you reach clipping, the protection circuit kicks in to limit current and save the output transistors. This makes the feedback circuit upset whose job is to make the input the same as output. So in turn it turns up the gain to counteract what the protection circuit is doing!

As the two fight another implicit feed look which is the power supply. In almost all amplifiers, the output stage runs unregulated meaning it starts with a high voltage but then sags as the load increases. Feedback in the amplifier makes it pretty immune to causing distortions. At clipping we have a new mess on our hand because now the power supply voltage goes up and down depending on what fighting is going on between the feedback loop and protection circuit.

In lay terms, there are three subsystem all working against each other with no coordination. The result is the twisted shape of the clipping and also oscillation which is shown in the first AVR.

The above is one of the reasons some folks don't like feedback. Feedback works great until you arrive at the above situation. It then works against you and makes the distortion worse, not better. So clipping that perhaps was benign is no longer so.

All of this can be avoided if you have ample amount of power available to you. Then you don't worry about the peaks.

Hope this makes sense. Please ask if it does not.

Pretty ridiculous IMHO.
This is operating the amps beyond their design limits, as evidenced by the clipping. It's like telling someone their VW Microbus won't work well if they drive off a cliff to reach 150 mph.

 

[Head_Unit]

what I believe to be behind such audibility differences namely what happens at clipping point which occurs far more often than we may think

A couple niggles...
- The authors must be confused about impedance. It's ribbons that have flat impedance. Planar magnetic I can't recall. Electrostatics tend to be capacitive, like this Acoustat in fact https://www.stereophile.com/content/acoustat-spectra-1100-loudspeaker-measurements
- They say an oscilloscope was used to determine there was clipping 1% of the time...but unless they used a much rarer storage oscilloscope I call poop on that, clipping can be too fast to determine something like "1%"
- I have begun wondering if peak-hold multimeters are fast enough to capture actual brief audio peaks-?!?!
- From some years of using The Power Cube for testing definitely if you have "100 watts" you are probably not getting that into real speakers. But it's not like 10 watts either.

I think one key area not tested is the effect of the protection circuit and power supply lag during peaks. Combine this with feedback and it gets ugly really fast.

I think you are right on that. There was actually a long-ago article* showing some really ugly behaviors, like voltage snapping from one supply rail to the other for a few milliseconds.
*maybe this? https://www.aes.org/e-lib/browse.cfm?elib=1671

However this is all getting away from the proposition that "below clipping" all amps sound pretty much the same. I suspect most people don't clip because they just don't play so super loud. But to answer

Pretty ridiculous IMHO...operating the amps beyond their design limits

That is true technically, but not necessarily an unfair test. If someone buys a 200W amp they would not be expecting clipping. The test is really more like "can you hear the difference between very powerful amplifiers that you would not expect to be clipping?" IF we accept the results as valid-i.e. the setup truly blind, statistics done properly, etc which I did not read enough and am not expert enough to judge-then amps played pretty loud CAN sound different, due to differing behaviors near maximum output.
What's needed is some convenient way of determining clipping: a phone oscilloscope app? A fast enough peak-hold meter? (which won't be definitive, but at least you can calculate if you are close to the amp's rail voltages or not even)

 

[Bloomer]

I was asking questions. Period. Someone show stats, please.

 

[DonH56]

A couple niggles...
- The authors must be confused about impedance. It's ribbons that have flat impedance. Planar magnetic I can't recall. Electrostatics tend to be capacitive, like this Acoustat in fact https://www.stereophile.com/content/acoustat-spectra-1100-loudspeaker-measurements

Ribbons and most planer dynamic speakers are essentially resistive in the audio band (and usually well beyond). They are just long wires, after all. However, many if not most have multiple elements and thus a crossover, which will introduce an impedance bump through the transition region(s).

The ESL panel itself is almost purely capacitive, but the transformer used to bias the panel and couple the audio signal is a big inductor. As a result, most ESLs look inductive at high frequencies if you look at their phase angle, although their impedance falls to very low levels.

- They say an oscilloscope was used to determine there was clipping 1% of the time...but unless they used a much rarer storage oscilloscope I call poop on that, clipping can be too fast to determine something like "1%"

Most folk these days use a DSO which will readily detect fast peaks. A 1 MHz DSO is fairly cheap, and 100+ kHz USB or sound-card based DSOs abound. Where they tend to fall down is in memory depth; you might have to aggregate multiple waveforms to get a statistically significant baseline for the amount of clipping. But still easy to do with modern 'scopes.

- I have begun wondering if peak-hold multimeters are fast enough to capture actual brief audio peaks-?!?!

Some are, some (perhaps most) aren't, if you are looking at very high (audio) frequency peaks. Most of the largest signals are in the bass where most (IME) multimeters can capture the peaks, but my experience is mainly with higher-end DMMs. I don't know about the $10~$50 crowd. Many cheap ones are designed to measure AC lines and not the audio band so have limited bandwidth, 150 Hz or less. Again IME.

 

[krabapple]

So apparently there was no harm in reviving this 2016 thread ... at least for a moment or two.

I can't challenge a person like Purite when they say that they have never heard any difference between properly designed amps working within design parameters for power, impedance load, etc.. They haven't, I have.

A big contributor, IMHO, is harmonic spectrum. It's observable that two amp can have basically identical SINAD but show quite different harmonics. I'd venture that blind tests would show that amp 'A' with high 2nd and/or 3rd order harmonics sounds different than amp 'B' with low 2nd/3rd but a forest of higher order will sound different to most people at least some of the time.

I can challenge anyone who has done such comparisons sighted only and not level-matched.

I have no idea why anyone wants more such reports published here. What is the point?

Will we ever learn?

 

[fpitas]

I was asking questions. Period. Someone show stats, please.

You convinced me. I've given up trying to understand anything.

 

[Bloomer]

You convinced me. I've given up trying to understand anything.

I imagine this discussion has been going on since around 1920. Hobbies should be fun. My daughter, who's in the Marines now, was/is a super Equestrian Eventer (stadium jumping, cross country, dressage); horsey people absolutely torture themselves for a hobby that has no end game. It's supposed to be fun! Happy Holidays.

 

[Gorgonzola]

I can challenge anyone who has done such comparisons sighted only and not level-matched.

I have no idea why anyone wants more such reports published here. What is the point?

Will we ever learn?

So are you suggesting the moderators ban all subjective comments? They have not done so to date but perhaps with enough pressure they might. Only speculation on my part, but I suspect in case of a big crackdown on subjective reporting that participation on this forum would drop significantly. (Good riddance to the dropouts you say? )

 

[SIY]

So are you suggesting the moderators ban all subjective comments? They have not done so to date but perhaps with enough pressure they might. Only speculation on my part, but I suspect in case of a big crackdown on subjective reporting that participation on this forum would drop significantly. (Good riddance to the dropouts you say? )

Perhaps it's best that extraordinary sonic claims offered without evidence are treated by the membership with the respect they deserve. It may be uncomfortable for the claimants, but the more intelligent ones will try to actually gather evidence rather than whine.

 

[fpitas]

the more intelligent ones will try to actually gather evidence rather than whine

Or at least think a little before they troll. I mean, share their views.

 

[Gorgonzola]

Perhaps it's best that extraordinary sonic claims offered without evidence are treated by the membership with the respect they deserve. It may be uncomfortable for the claimants, but the more intelligent ones will try to actually gather evidence rather than whine.

But who's whining now? Seems to be the people who don't want to hear subjective impressions.

My advice remains the same: if you don't like subjective comments, you may simply ignore them instead of constantly & repetitiously deriding them.

 

[SIY]

But who's whining now? Seems to be the people who don't want to hear subjective impressions.

My advice remains the same: if you don't like subjective comments, you may simply ignore them instead of constantly & repetitiously deriding them.

I'm sorry this is happening to you.

 

[Frank Dernie]

But who's whining now? Seems to be the people who don't want to hear subjective impressions.

My advice remains the same: if you don't like subjective comments, you may simply ignore them instead of constantly & repetitiously deriding them.

Almost all HiFi forums expect and respect subjective comments.
This one is almost unique and generally known to be.

It is almost trolling to put a subjective comment on here without sound evidence and expect it to be taken seriously.

 

[DonR]

No issues with subjective comments as long as they are not held up as evidence. I'll throw in one myself. I have heard differences in amplifiers at higher spl driving "difficult" speakers. At my preferred listening level, I don't hear any differences.

 

[fpitas]

as long as they are not held up as evidence

Exactly

 

[Ken1951]

Almost all HiFi forums expect and respect subjective comments.
This one is almost unique and generally known to be.

It is almost trolling to put a subjective comment on here without sound evidence and expect it to be taken seriously.

And those same forums almost automatically delete any reference to blind listening tests or level matching. Such comments if not deleted are intensely flamed immediately and the poster derided without mercy.

 

[Killingbeans]

My advice remains the same: if you don't like subjective comments, you may simply ignore them instead of constantly & repetitiously deriding them.

I wouldn't mind doing that. But only if they weren't constantly & repetitiously being presented as useful data points.

Anecdotes being pushed as facts should not be ignored. Otherwise they'll end up smothering all the things that are actually useful.

 

[fpitas]

Anecdotes being pushed as facts should not be ignored. Otherwise they'll end up smothering all the things that are actually useful.

Yes; otherwise ASR will go down under an avalanche of garbage like other audio sites.