[Bill-P]

  Generalizations are made ALL THE TIME in scientific journals. It's why every other year eggs will either kill us or make us live longer. And my current subjective impression of amps is that, for the phones I have, my amps don't make a shred of difference to the music; hence why I offered to properly ABX them, though that would require equipment.

 
Scientific journals should be a report of observations made during a research and not as a tool to draw "facts" from, so I'm not sure where you are seeing generalizations being made in there. Perhaps if you can point to one?
 
And I have already said that to you, your subjective impressions should matter more so than some ABX test. Meaning... you should not have to conduct the test to begin with. If you think, or you feel, that there is no difference between your amps, then there is really no merit in you trying to conduct a test yourself. What would you be able to prove? That a statement you yourself made is factually correct... for yourself?
 

  are you losing yourself for the sake of the argument, or do you really intend to tell us that uncontrolled personal experience of a gear is more reliable than a controlled one?
 
about your answer to stv014 before, your "demonstration" never showed that amps sounded different, it demonstrated that amps could have different impedances. it's really not the same thing. and the differences came from the IEM in fact, not from the amp. else the IE8 would also have suffered from the effect as it's a low impedance IEM too. but it just didn't, showing that the amps just did what they were asked to do.
about the O2, given the number of nwavguy haters for no reason at all, do you really think that they didn't already try all they could to find some problems here and there on the O2? it's one of the most documented amp you can find, certainly me playing with strange signs such as + - and / (I've done more math in the last week than I did in 10years and it shows

)isn't going to uncover anything new. I personally just accept the fact that I mixed approximate values taken from 2 different sources and just that is enough for some variations to be expected.

 
Well, no. I don't really see how I can word it differently, but here goes: my subjective impressions and experience of a piece of gear should be more important than someone else's ABX test results of said gears.
 
Now the caveat is simply that if I end up doing an ABX test and find there being no difference, then that means my subjective impressions and experience have changed, but that does not make them any less important to me, nor does that make them any more important to the next guy over. Right?
 
And an amp needs a headphone, or IEM, or speaker to play back sound, or to "sound different", so if we are not comparing in that context, then how exactly will amplifiers by themselves "sound different"? Do you have any other way to "listen" to an amplifier without using IEM, headphone, or speakers, perhaps?
 
Regarding the O2, there are some who have mentioned its problems at a glance (input level above 2.0Vrms may cause problems, for instance), but none of them has had the time to go in and dissect the results the same way its author spent time to dissect other products. Although occasionally, there are measurements here and there like the one I just showed you.
 
You must realize that not everyone who disagrees with its author is a disgruntled engineer hell-bent on making a better product, and needing the numbers as a marketing tool. Not everyone is seeking fame or creds.

 

[RRod]

   
Scientific journals should be a report of observations made during a research and not as a tool to draw "facts" from, so I'm not sure where you are seeing generalizations being made in there. Perhaps if you can point to one?
 
And I have already said that to you, your subjective impressions should matter more so than some ABX test. Meaning... you should not have to conduct the test to begin with. If you think, or you feel, that there is no difference between your amps, then there is really no merit in you trying to conduct a test yourself. What would you be able to prove? That a statement you yourself made is factually correct... for yourself?
 

 
Ever used an over-the-counter drug? There you go, you're swallowing a generalization made to a population based upon a sample. You can nitpick and say that it's organizations making the generalizations based upon the numbers in the papers, but the whole reason the researchers are gathering such numbers is to allow for the generalization.
 
My saying "subjectively I haven't heard a difference between amps" is not factual. False negatives happen just as well as false positives. The point of doing a test is to add rigor that allows for accounting of such false outcomes.
 
Also, I think I've reached "call it a day and have a club soda with lemon" with you. Enjoy your amps 

 

 

[Bill-P]

   
Ever used an over-the-counter drug? There you go, you're swallowing a generalization made to a population based upon a sample. You can nitpick and say that it's organizations making the generalizations based upon the numbers in the papers, but the whole reason the researchers are gathering such numbers is to allow for the generalization.
 
My saying "subjectively I haven't heard a difference between amps" is not factual. False negatives happen just as well as false positives. The point of doing a test is to add rigor that allows for accounting of such false outcomes.
 
Also, I think I've reached "call it a day and have a club soda with lemon" with you. Enjoy your amps 

 

I think we are talking about different things with regards to "generalization" there. ABX test is far from something anyone would use to create a headphone or an amp... so I don't think it applies in this context. But let's drop it, as it's inconsequential to the discussion.
 
And I didn't say that your statement was factual. Doing the test will verify that it is factual, yes, but it is only factual when it's concerning you. It still may not apply to other folks.
 
Remember this saying? "Whether you think you can, or you can't, you are right"?
 
It's all about your own subjective impressions, which... I have said for so long now.
 
And anyway, I'm enjoying my amp alright. I built it myself after all, for $150 worth of parts... and it does the job just fine for my relatively hard to drive planar magnetic headphone. I'm glad I didn't have to spend $500 to purchase another amp powerful enough for this task.

 

[castleofargh]

  Well, no. I don't really see how I can word it differently, but here goes: my subjective impressions and experience of a piece of gear should be more important than someone else's ABX test results of said gears.
 
Now the caveat is simply that if I end up doing an ABX test and find there being no difference, then that means my subjective impressions and experience have changed, but that does not make them any less important to me, nor does that make them any more important to the next guy over. Right?

 
 
 I think that my girlfriend is a perfect, and to me she is. but neither my opinion, nor her look would get her on a victorya's secret catalog.
 
that's the difference between how I see the world and how it really is.
when I'm alone with my headphone, I'm the king of my castle and I can think whatever I want and convince myself it's true. if it makes me happier, who cares what is true. but when I'm on a public forum, I try to first check that what I claim to be a reality also exists outside of my head. a controlled test is one very relevant and repeatable way to do that. but many many audiophiles don't bother checking and come telling us all about their dreams thinking they're still sleeping.

   
And an amp needs a headphone, or IEM, or speaker to play back sound, or to "sound different", so if we are not comparing in that context, then how exactly will amplifiers by themselves "sound different"? Do you have any other way to "listen" to an amplifier without using IEM, headphone, or speakers, perhaps?

come on now. not using a less than 16ohm IEM with huge impedance variations over frequencies, that could be a good start to test normal behavior of an amp.
many headphones have a flat or almost flat impedance response. any of those within power specs for the amp would do just fine. and in fact many others with impedance variations would also do just fine. like my hd650, it has a pretty huge bump in impedance at 100hz, but going from a 1ohm amp to a 5ohm amp would probably not even make a 0.1db change(didn't check with numbers this time but I would guess less than 0.1db). and that's a much bigger change than going from 0.4 to 0.54. that is to say how extreme your example was.
 
we can see it as manufacturers making dumb and unreliable IEMs, or we can accept that 0.5db is probably less than the left/right deviation you'll get from one pair of IEM, or the change in sound once the filters get dirty. or we can even decide to blame the amps for not all being 0.1ohm(some are).
from my point of view, almost all kinds of amps and headphones exist, but if I use the proper ones for the proper headphone, then they should sound the same and sound transparent. if they are good amps that's how it should be and how it is most of the time.
colored amps are something else, they **** up on purpose.
 
and of course to test 2amps we can use some purely resistive loads and measure the crap out of them. that would actually tell us a lot more than any listening could about the real differences between 2 amps.

 

[bigshot]

  I think the regulars in sound science have done their time with testing and simply try to preach truth. It's not their fault that rigorous testing, both statistical and non-statistical, still can't convince people of things. It's just human nature, I guess.

 
If they won't be convinced by the accumulated data from peer reviewed testing, arguing with them about the value of blind testing or proper ABX procedures really isn't going to help. That's when you pat them on the head and send them on their way.

 

[Bill-P]

  I think that my girlfriend is a perfect, and to me she is. but neither my opinion, nor her look would get her on a victorya's secret catalog.
 
that's the difference between how I see the world and how it really is.
when I'm alone with my headphone, I'm the king of my castle and I can think whatever I want and convince myself it's true. if it makes me happier, who cares what is true. but when I'm on a public forum, I try to first check that what I claim to be a reality also exists outside of my head. a controlled test is one very relevant and repeatable way to do that. but many many audiophiles don't bother checking and come telling us all about their dreams thinking they're still sleeping.
come on now. not using a less than 16ohm IEM with huge impedance variations over frequencies, that could be a good start to test normal behavior of an amp.
many headphones have a flat or almost flat impedance response. any of those within power specs for the amp would do just fine. and in fact many others with impedance variations would also do just fine. like my hd650, it has a pretty huge bump in impedance at 100hz, but going from a 1ohm amp to a 5ohm amp would probably not even make a 0.1db change(didn't check with numbers this time but I would guess less than 0.1db). and that's a much bigger change than going from 0.4 to 0.54. that is to say how extreme your example was.
 
we can see it as manufacturers making dumb and unreliable IEMs, or we can accept that 0.5db is probably less than the left/right deviation you'll get from one pair of IEM, or the change in sound once the filters get dirty. or we can even decide to blame the amps for not all being 0.1ohm(some are).
from my point of view, almost all kinds of amps and headphones exist, but if I use the proper ones for the proper headphone, then they should sound the same and sound transparent. if they are good amps that's how it should be and how it is most of the time.
colored amps are something else, they **** up on purpose.
 
and of course to test 2amps we can use some purely resistive loads and measure the crap out of them. that would actually tell us a lot more than any listening could about the real differences between 2 amps.

 
I don't think the majority of folks here come to relay information and push them as "facts". Rather, the abundance of impressions are there just so people can read and consider them. Due to that, there is really no need for them to fact-check because... again, they are not trying to push "facts".
 
And I don't think there is any rule here against posting an opinion, whether right or wrong, so they are entirely entitled to do just that.
 
If you end up doing an ABX test, and get a no-difference result, then that's great. Now you have discovered a "fact", but the "fact" only applies to you, your gears, and your conditions. Someone else who lives in an entirely different country, who uses an entirely different setup in an entirely different place may hear something you may not. Does that make you or him a liar? No... it just means your fact doesn't apply to him.
 
So in that regard, once again, I find an ABX test not really that necessary even for relaying audio impressions. But you may think otherwise, and you are certainly entitled to do so.
 
And ahem... not many headphones have a flat or almost flat impedance plot. The HD800, for instance, has an impedance plot that spikes up to 650 Ohm and goes as low as 350 Ohm. The DT880 250 Ohm goes as high as 300 Ohm and as low as 230 Ohm or so. Sennheiser HD600 has a spike at 550 Ohm, and its nominal is about 300 Ohm. If it's a dynamic headphone, it'll always have an impedance curve of some sort. IEMs impedance swing isn't that crazy from what I have seen, but look at those big headphones. Impedance swing can be as high 300 Ohm. So it's not that manufacturers are dumb and that they can't manufacture the right IEM.
 
So I'll have to ask you... what would be considered a "proper" amp in this regard? Something with 0.1 Ohm output impedance? Would you mind pointing to one? Because I haven't seen it yet.
 
And now... if you measure 2 amps with purely resistive loads and see some differences in the measurements, would you say the amps are different, or are you going to claim "the differences are inaudible" without even trying the amps yourself?
 
And if you do end up trying the amp and finding no difference, please note: the differences can still be measured.
 
Sigh...
 
I feel like I'm going around in circles here.

 

[Head Injury]

   
I don't think the majority of folks here come to relay information and push them as "facts". Rather, the abundance of impressions are there just so people can read and consider them. Due to that, there is really no need for them to fact-check because... again, they are not trying to push "facts".
 
And I don't think there is any rule here against posting an opinion, whether right or wrong, so they are entirely entitled to do just that.
 
If you end up doing an ABX test, and get a no-difference result, then that's great. Now you have discovered a "fact", but the "fact" only applies to you, your gears, and your conditions. Someone else who lives in an entirely different country, who uses an entirely different setup in an entirely different place may hear something you may not. Does that make you or him a liar? No... it just means your fact doesn't apply to him.
 
So in that regard, once again, I find an ABX test not really that necessary even for relaying audio impressions. But you may think otherwise, and you are certainly entitled to do so.

Which is one of the reasons why we ask the ones making the claims to take their own tests. Then the results apply to them.
 
And, of course, everything you said here about two people hearing two different things applies doubly to subjective impressions. At least ABX tests take sighted bias out of the equation. I hope you're not suggesting that we shouldn't trust ABX tests but subjective impressions are OK.
 

  And ahem... not many headphones have a flat or almost flat impedance plot. The HD800, for instance, has an impedance plot that spikes up to 650 Ohm and goes as low as 350 Ohm. The DT880 250 Ohm goes as high as 300 Ohm and as low as 230 Ohm or so. Sennheiser HD600 has a spike at 550 Ohm, and its nominal is about 300 Ohm. If it's a dynamic headphone, it'll always have an impedance curve of some sort. IEMs impedance swing isn't that crazy from what I have seen, but look at those big headphones. Impedance swing can be as high 300 Ohm. So it's not that manufacturers are dumb and that they can't manufacture the right IEM.
 
So I'll have to ask you... what would be considered a "proper" amp in this regard? Something with 0.1 Ohm output impedance? Would you mind pointing to one? Because I haven't seen it yet.
 
And now... if you measure 2 amps with purely resistive loads and see some differences in the measurements, would you say the amps are different, or are you going to claim "the differences are inaudible" without even trying the amps yourself?
 
And if you do end up trying the amp and finding no difference, please note: the differences can still be measured.
 
Sigh...
 
I feel like I'm going around in circles here.

The difference in volume between 650 and 350 ohms is much smaller than the difference between 10 and 100 ohms, even assuming the output impedance changes to scale. The volume difference is based on a ratio of voltage, not number of ohms.
 
Put another way to make the math easier, the changes to frequency response from a 1 ohm output impedance on a headphone going from 65 to 35 ohms will be exactly the same as the change a 10 ohm output impedance will cause on a 650/350 headphone even though both the output impedance and difference in load impedance are 10 times as high, because the ratio is the same. In that sense, and because higher impedances are affected less by output impedance, the high end Senns and Beyers are quite tame compared to multi-BA IEMs.
 
If you want a full-sized headphone example, the most extreme case I can think of is the Sennheiser HD598. It goes from about 50 to 300 ohm impedance. It will undergo a maximum volume difference of 0.83 dB with 6.25 ohm output impedance, which is the 1/8 rule impedance. This is the highest I know of outside multi-BA IEMs as far as the effect a 1/8 impedance creates, but there will no doubt be some very low impedance full-sized headphones that will change more with a 6.25 ohm output impedance. The HD800, assuming 350 and 650 ohms and a 43.75 ohm output impedance (1/8 again), will undergo a 0.46 dB change.
 
To answer your question of what's acceptable, with the HD800 I would call about 40 ohm output impedance acceptable, but lower is always better. 10 ohms is pretty common and will create a tiny 0.11 dB volume difference. It's not hard to find amps with 1 ohm impedance or lower, might as well go with one of those for maximum compatibility (but not always complete transparency as we've seen in the extreme examples in this thread).
 
Where did anyone say that amps have no measurable differences? You seem to want us to acknowledge that they have measurable differences. They do, virtually all of them do. Measurable isn't always audible though, no matter how many times you try to berate us for saying so. I don't need to listen to every amp in the world to know that human hearing is less accurate than a dScope.

 

[RRod]

  Which is one of the reasons why we ask the ones making the claims to take their own tests. Then the results apply to them.
 
And, of course, everything you said here about two people hearing two different things applies doubly to subjective impressions. At least ABX tests take sighted bias out of the equation. I hope you're not suggesting that we shouldn't trust ABX tests but subjective impressions are OK.
 
The difference in volume between 650 and 350 ohms is much smaller than the difference between 10 and 100 ohms, even assuming the output impedance changes to scale. The volume difference is based on a ratio of voltage, not number of ohms.
 
Put another way to make the math easier, the changes to frequency response from a 1 ohm output impedance on a headphone going from 65 to 35 ohms will be exactly the same as the change a 10 ohm output impedance will cause on a 650/350 headphone even though both the output impedance and difference in load impedance are 10 times as high, because the ratio is the same. In that sense, and because higher impedances are affected less by output impedance, the high end Senns and Beyers are quite tame compared to multi-BA IEMs.
 
If you want a full-sized headphone example, the most extreme case I can think of is the Sennheiser HD598. It goes from about 50 to 300 ohm impedance. It will undergo a maximum volume difference of 0.83 dB with 6.25 ohm output impedance, which is the 1/8 rule impedance. This is the highest I know of outside multi-BA IEMs as far as the effect a 1/8 impedance creates, but there will no doubt be some very low impedance full-sized headphones that will change more with a 6.25 ohm output impedance. The HD800, assuming 350 and 650 ohms and a 43.75 ohm output impedance (1/8 again), will undergo a 0.46 dB change.
 
To answer your question of what's acceptable, with the HD800 I would call about 40 ohm output impedance acceptable, but lower is always better. 10 ohms is pretty common and will create a tiny 0.11 dB volume difference. It's not hard to find amps with 1 ohm impedance or lower, might as well go with one of those for maximum compatibility (but not always complete transparency as we've seen in the extreme examples in this thread).
 
Where did anyone say that amps have no measurable differences? You seem to want us to acknowledge that they have measurable differences. They do, virtually all of them do. Measurable isn't always audible though, no matter how many times you try to berate us for saying so. I don't need to listen to every amp in the world to know that human hearing is less accurate than a dScope.

 
The HDVD800 (the HD800s companion DAC/amp) is listed as 16ohm minimum output impedance, but for some reason on certain reviews I've seen it given as ~43ohm; wonder if someone just back-calculated that or if it's measured that high above the minimum listing.

 

[Bill-P]

  Which is one of the reasons why we ask the ones making the claims to take their own tests. Then the results apply to them.
 
And, of course, everything you said here about two people hearing two different things applies doubly to subjective impressions. At least ABX tests take sighted bias out of the equation. I hope you're not suggesting that we shouldn't trust ABX tests but subjective impressions are OK.
 
The difference in volume between 650 and 350 ohms is much smaller than the difference between 10 and 100 ohms, even assuming the output impedance changes to scale. The volume difference is based on a ratio of voltage, not number of ohms.
 
Put another way to make the math easier, the changes to frequency response from a 1 ohm output impedance on a headphone going from 65 to 35 ohms will be exactly the same as the change a 10 ohm output impedance will cause on a 650/350 headphone even though both the output impedance and difference in load impedance are 10 times as high, because the ratio is the same. In that sense, and because higher impedances are affected less by output impedance, the high end Senns and Beyers are quite tame compared to multi-BA IEMs.
 
If you want a full-sized headphone example, the most extreme case I can think of is the Sennheiser HD598. It goes from about 50 to 300 ohm impedance. It will undergo a maximum volume difference of 0.83 dB with 6.25 ohm output impedance, which is the 1/8 rule impedance. This is the highest I know of outside multi-BA IEMs as far as the effect a 1/8 impedance creates, but there will no doubt be some very low impedance full-sized headphones that will change more with a 6.25 ohm output impedance. The HD800, assuming 350 and 650 ohms and a 43.75 ohm output impedance (1/8 again), will undergo a 0.46 dB change.
 
To answer your question of what's acceptable, with the HD800 I would call about 40 ohm output impedance acceptable, but lower is always better. 10 ohms is pretty common and will create a tiny 0.11 dB volume difference. It's not hard to find amps with 1 ohm impedance or lower, might as well go with one of those for maximum compatibility (but not always complete transparency as we've seen in the extreme examples in this thread).
 
Where did anyone say that amps have no measurable differences? You seem to want us to acknowledge that they have measurable differences. They do, virtually all of them do. Measurable isn't always audible though, no matter how many times you try to berate us for saying so. I don't need to listen to every amp in the world to know that human hearing is less accurate than a dScope.

Oh no, I have repeatedly said that subjective impressions should not be trusted. What I'm simply saying is that... whether there is an ABX test or not, and whatever someone else say, the best way to really know about a piece of gear is to actually own, or try it.
 
Measurable is indeed not always audible, but how would you know? By reading someone else's ABX results and deduce it from there? Or from looking at measurements made with perfect resistive loads?

 

[Bill-P]

  The HDVD800 (the HD800s companion DAC/amp) is listed as 16ohm minimum output impedance, but for some reason on certain reviews I've seen it given as ~43ohm; wonder if someone just back-calculated that or if it's measured that high above the minimum listing.

 
Well, I was hoping to avoid this, but it is also possible for output impedance to vary with frequency. Hence why it's "impedance" and not "resistance". And also why it's somewhat okay for Sennheiser to list 16 Ohm "minimum", but it could obviously vary.
 
Naturally, this will also bring up another problem: the given output impedance that a manufacturer gives may or may not be correct, and that some amplifiers may in fact have an output impedance curve as well. When this curve interacts with the headphone, it gives some really interesting (and often undesirable) effects beyond just EQ depending on how the circuit is implemented so that output impedance varies like that.
 
I don't want to say bad things about the HD800 because it's a fantastic headphone outright, but I can't help but think Sennheiser has obviously designed it with some screwy headphone amp circuitry in mind.
 
I did listen to the HD800 out of the HDVD800, though, and the "pairing" really does sound good, but that "sound" is not how the HD800 sounds naturally, because I have heard the HD800 with other "more transparent" amps, and I could never stand the sound of a stock HD800.

 

[castleofargh]

 

   
I don't think the majority of folks here come to relay information and push them as "facts". Rather, the abundance of impressions are there just so people can read and consider them. Due to that, there is really no need for them to fact-check because... again, they are not trying to push "facts".
 
And I don't think there is any rule here against posting an opinion, whether right or wrong, so they are entirely entitled to do just that.
 
If you end up doing an ABX test, and get a no-difference result, then that's great. Now you have discovered a "fact", but the "fact" only applies to you, your gears, and your conditions. Someone else who lives in an entirely different country, who uses an entirely different setup in an entirely different place may hear something you may not. Does that make you or him a liar? No... it just means your fact doesn't apply to him.
 
So in that regard, once again, I find an ABX test not really that necessary even for relaying audio impressions. But you may think otherwise, and you are certainly entitled to do so.

Which is one of the reasons why we ask the ones making the claims to take their own tests. Then the results apply to them.
 
And, of course, everything you said here about two people hearing two different things applies doubly to subjective impressions. At least ABX tests take sighted bias out of the equation. I hope you're not suggesting that we shouldn't trust ABX tests but subjective impressions are OK.
 

  And ahem... not many headphones have a flat or almost flat impedance plot. The HD800, for instance, has an impedance plot that spikes up to 650 Ohm and goes as low as 350 Ohm. The DT880 250 Ohm goes as high as 300 Ohm and as low as 230 Ohm or so. Sennheiser HD600 has a spike at 550 Ohm, and its nominal is about 300 Ohm. If it's a dynamic headphone, it'll always have an impedance curve of some sort. IEMs impedance swing isn't that crazy from what I have seen, but look at those big headphones. Impedance swing can be as high 300 Ohm. So it's not that manufacturers are dumb and that they can't manufacture the right IEM.
 
So I'll have to ask you... what would be considered a "proper" amp in this regard? Something with 0.1 Ohm output impedance? Would you mind pointing to one? Because I haven't seen it yet.
 
And now... if you measure 2 amps with purely resistive loads and see some differences in the measurements, would you say the amps are different, or are you going to claim "the differences are inaudible" without even trying the amps yourself?
 
And if you do end up trying the amp and finding no difference, please note: the differences can still be measured.
 
Sigh...
 
I feel like I'm going around in circles here.

The difference in volume between 650 and 350 ohms is much smaller than the difference between 10 and 100 ohms, even assuming the output impedance changes to scale. The volume difference is based on a ratio of voltage, not number of ohms.
 
Put another way to make the math easier, the changes to frequency response from a 1 ohm output impedance on a headphone going from 65 to 35 ohms will be exactly the same as the change a 10 ohm output impedance will cause on a 650/350 headphone even though both the output impedance and difference in load impedance are 10 times as high, because the ratio is the same. In that sense, and because higher impedances are affected less by output impedance, the high end Senns and Beyers are quite tame compared to multi-BA IEMs.
 
If you want a full-sized headphone example, the most extreme case I can think of is the Sennheiser HD598. It goes from about 50 to 300 ohm impedance. It will undergo a maximum volume difference of 0.83 dB with 6.25 ohm output impedance, which is the 1/8 rule impedance. This is the highest I know of outside multi-BA IEMs as far as the effect a 1/8 impedance creates, but there will no doubt be some very low impedance full-sized headphones that will change more with a 6.25 ohm output impedance. The HD800, assuming 350 and 650 ohms and a 43.75 ohm output impedance (1/8 again), will undergo a 0.46 dB change.
 
To answer your question of what's acceptable, with the HD800 I would call about 40 ohm output impedance acceptable, but lower is always better. 10 ohms is pretty common and will create a tiny 0.11 dB volume difference. It's not hard to find amps with 1 ohm impedance or lower, might as well go with one of those for maximum compatibility (but not always complete transparency as we've seen in the extreme examples in this thread).
 
Where did anyone say that amps have no measurable differences? You seem to want us to acknowledge that they have measurable differences. They do, virtually all of them do. Measurable isn't always audible though, no matter how many times you try to berate us for saying so. I don't need to listen to every amp in the world to know that human hearing is less accurate than a dScope.

what Head Injury said. all of it!
and I would add :
orthos tend to have a flat impedance response. and dynamic headphones still have smaller variations than most multi BA IEMs. and it's logic. even those you mentioned could be used to test some amps and the deviations would be trivial on the majority of them. and it would mostly be a small FR change anyway, not noise or whatever. 
it's really all about having a good "synergy"

 
to me the need to test an amp is purely for when I can't find enough specs or if the manufacturer is too vague with the units. but I tend to distrust manufacturers who are not open with specs, so I probably wouldn't want to listen to the amp anyway if I knew nothing about it.
 
and I said 0.1ohm because I was thinking about benchmark DAC/amp when I wrote the post. but hugo has specs at 0.075ohm.

 

[Dark_wizzie]

 
EQ never was intended to extend frequencies. that will never work and only make the headphone turn into crap. but now there are many headphones with less than 10db differences over most of the 50hz to say 14khz, and the never ending debate is about knowing if you can take one headphone and make it sound a lot like the other one?
the answer to that is clearly yes. but then some say that you can, not only have about the same sound signature, but also make the decay of each frequencies closer thanks to the EQ alone. and Vid showed us that it happened and that balancing a signature could also balance the decay differences. I also think I saw the opposite idea once, so I would guess that it might depend on a few parameters. but having the same king of headphone(dynamic, open back, about the same size...) should lead to several situations where you can almost turn one headphone into another one. it just seems logical to me. just like in some instances, you couldn't do it will all the DSP's in the world(tuning a porta pro into a hd800 might be slightly problematic ^_^).
so the right answer is probably "it depends". but the audio world doesn't like "it depends" conclusions ^_^.
 
on a very subjective level,I know that I often feel a little change in soundstage between 2 EQ settings. it proves nothing but it let me believe that EQ can do more than just make the guitar louder.

I'm sure EQ can do great things... if done very, very well. Imagine a typical user that barely even knows what EQ is. There is no easy magic button that makes it all work right. It's confusing and a lot of work, especially to make one headphone sound like another I would imagine. So to me this discussion just feels academic, not much to do with changing how I go about my music.

 

[bigshot]

  I'm sure EQ can do great things... if done very, very well. Imagine a typical user that barely even knows what EQ is. There is no easy magic button that makes it all work right. It's confusing and a lot of work, especially to make one headphone sound like another I would imagine. So to me this discussion just feels academic, not much to do with changing how I go about my music.

How interested are you in getting working to get better sound quality? That's the question.