[RRod]

  Uhm, the O2 has 0.5 Ohm output impedance (from schematic), and the Leckerton UHA-6S Mk.II is quoted as having also 0.5 Ohm (I've also measured this from when I owned the UHA-6S Mk.II).
 
So no, they don't have different output impedance. If there is any difference, it's too small.
 
And the impedance swing of the UERM doesn't get below 5 Ohm, so based on that, it has more than a 1/10 ratio with both amps (orange plot is UERM's impedance):
 

 
How "rule of thumb" is the 1:10 ratio, though? It is odd that it's exactly where the impedance of the cans drops to its lowest that we eyeball the most difference between the amps. Innerfidelity gives the output impedance of the UHA as 0.4ohm, so could it be the case that this difference (0.4 vs 0.54) at these frequencies, where the headphones drop right to the "rule of thumb" realm, might start making a difference? I'm just asking; someone with da EE skillz can weigh in on the answer.

 

[Roly1650]

   
How "rule of thumb" is the 1:10 ratio, though? It is odd that it's exactly where the impedance of the cans drops to its lowest that we eyeball the most difference between the amps. Innerfidelity gives the output impedance of the UHA as 0.4ohm, so could it be the case that this difference (0.4 vs 0.54) at these frequencies, where the headphones drop right to the "rule of thumb" realm, might start making a difference? I'm just asking; someone with da EE skillz can weigh in on the answer.

But look at the frequency response graph and the scale on the y axis. We are talking about a maximum difference between these two amps and with only one phone of 0.75dB at 7.5kHz. Is that an audible difference, maybe with test tones, but on a music signal? Maybe, under certain circumstances, but we're not talking about a major fail. You can do wonderful things with graphs by buggering about with the scale.

 

[Bill-P]

  How "rule of thumb" is the 1:10 ratio, though? It is odd that it's exactly where the impedance of the cans drops to its lowest that we eyeball the most difference between the amps. Innerfidelity gives the output impedance of the UHA as 0.4ohm, so could it be the case that this difference (0.4 vs 0.54) at these frequencies, where the headphones drop right to the "rule of thumb" realm, might start making a difference? I'm just asking; someone with da EE skillz can weigh in on the answer.

 
Do note that the lowest impedance of the UERM from the plot above and many others is more like ~8 Ohm, so the damping factor for both amps should far exceed 1:10, unless I missed something.
 
And if you say 0.14 Ohm of output impedance makes a difference, then... what would that say about amps that have 2, 3, 4, 5, 10, 12, 20, 40 Ohm output impedance?
 
What would it say about audibility of differences in amps in general? Would all amps still sound the same now that you know this fact?
 

 
Quick note so that we can go back to the right topic at hand: this is far from just an EQ effect imposed on the headphone. It messes with the signal that's being sent more akin to a complicated DSP.
 
Here's an article on that:
http://www.innerfidelity.com/content/musings-headphone-amplifier-output-impedance
 
EQ both in hardware and in software should not work in this way, so if you ever come across this, it's either by pure accident that the system interacts in that way (synergy?), or the amp's designer (and headphone's manufacturer?) intended for that to begin with.
 
I am of the same opinion as Tyll, and that is... the acoustic dampening of the headphone would still make more of a difference than output impedance. Also, I have measured pretty much the same thing that Tyll has, and that is... output impedance really doesn't give much of a difference when the variation is small (0.1 Ohm is very very small change), and that's why I do not think the cause of the difference is due to output impedance. But who knows, I may just be on to the wrong thing here, and maybe the "rule" is not 1:10 but more like 1:20, 1:30 something...
 
Last note: this "rule" was 1:8 just a while earlier. So... yeah, something to mule on.
 

 

 

[castleofargh]

Uhm, the O2 has 0.5 Ohm output impedance (from schematic), and the Leckerton UHA-6S Mk.II is quoted as having also 0.5 Ohm (I've also measured this from when I owned the UHA-6S Mk.II).

So no, they don't have different output impedance. If there is any difference, it's too small.

And the impedance swing of the UERM doesn't get below 5 Ohm, so based on that, it has more than a 1/10 ratio with both amps (orange plot is UERM's impedance):

I would doubt myself if the changes didn't fit so well with the impedance curves. so I looked into it as well as I could.
so google my buddy gave me the O2 as 0.54ohm, and I found one leckerton value at 0.4ohm(but I don't even know if it's the same model ^_^, still I'll go with that).

the graph you give isn't the uerm http://rinchoi.blogspot.fr/2012/11/ultimate-ears-custom-in-ear-reference.html it doesn't change your point but I'd rather calculate with the good values.
having about 1/10 of damping ratio doesn't protect from change, it reduces the values. and again the better the damping the smaller the differences. but you're right I wrote it as if it was absolute protection, sorry for not being clear enough.

now let's see:

let's say I send 0.1v using both amps and the UERM. I'll take the 2 extrem values of impedance to show the max possible difference:
at 8khz it's 12ohm
from the O2 it's 0.1*12/(12+0.54)=0.0957v
from the leck if it's 0.4ohm??? 0.1*12/(12+0.4)=0.0968v




same at 500hz it's 80ohm
o2 0.1*80/(80+0.54)=0.0993v
leckerton(maybe? ^_^) 0.1*80/(80+0.4)=0.0995v


so for the o2 we'll get voltage ratio between both frequencies of 0.0957/0.0993=0.9637 that's 0.32db variation
sam for the leckerton: 0.0968/0.0995=0.9728 that's 0.24db
so the difference from both amps should be no more than 0.1db
so something isn't right and if the variation could fit for the leckerton, it doesn't for the O2 where the variation looks more like maybe -0.6db to me on the graph between 500hz and 8khz.

-0.6db that's a voltage ratio of 0.9332

if we imagine the O2 was 1ohm instead of 0.54 then we'd get 0.0923/0.09875=0.9347, that's -0.58db. so unless I messed up somewhere, that would be a more likely value(maybe some cable impedance and in fact the leckerton is even lower?) .
now I don't know how the measurements were done on the graph you gave with all the IEMs variations, and there are uncertainties like sure values for both amps or me failling somewhere along the road ^_^. but at least you can see how you don't need all that much to have an audible difference as long as you use messed up IEMs for your test.
that's why the RMAA from markuskraus.com were always done with triple fi10. because they had a really low and wild impedance response so it revealed the DAPs with high impedance without having to really measure it.

now I did all that because I'm a masochist(obviously), but you realize that even with extreme IEMs very likely to be affected, the changes are still below 1db in that situation. the graph looks frightening, but I doubt many people can hear less than 1db change if not in a direct comparison.

 

[RRod]

   
Do note that the lowest impedance of the UERM from the plot above and many others is more like ~8 Ohm, so the damping factor for both amps should far exceed 1:10, unless I missed something.
 
And if you say 0.14 Ohm of output impedance makes a difference, then... what would that say about amps that have 2, 3, 4, 5, 10, 12, 20, 40 Ohm output impedance?
 
What would it say about audibility of differences in amps in general? Would all amps still sound the same now that you know this fact?
 

 
Quick note so that we can go back to the right topic at hand: this is far from just an EQ effect imposed on the headphone. It messes with the signal that's being sent more akin to a complicated DSP.
 
Here's an article on that:
http://www.innerfidelity.com/content/musings-headphone-amplifier-output-impedance
 
EQ both in hardware and in software should not work in this way, so if you ever come across this, it's either by pure accident that the system interacts in that way (synergy?), or the amp's designer (and headphone's manufacturer?) intended for that to begin with.
 
I am of the same opinion as Tyll, and that is... the acoustic dampening of the headphone would still make more of a difference than output impedance. Also, I have measured pretty much the same thing that Tyll has, and that is... output impedance really doesn't give much of a difference when the variation is small (0.1 Ohm is very very small change), and that's why I do not think the cause of the difference is due to output impedance. But who knows, I may just be on to the wrong thing here, and maybe the "rule" is not 1:10 but more like 1:20, 1:30 something...
 
Last note: this "rule" was 1:8 just a while earlier. So... yeah, something to mule on.
 

 

 
Well that's why I said "I'm just asking". And I don't think anyone has ever said "all amps will sound the same with all headphones at all frequencies"; I would think the understood caveat is "all amps that satisfy the power requirements for a set of cans and that are well outside of any 'rule of thumb' issues with impedance sound the same." Hence why I was asking about any possible rule of thumb issues, as I would imagine there's a reason that 1:8 or 1:10 or whatever is a "rule of thumb" instead of "a law." And what I think about amps with umpteen ohms output impedance is that if my headphones have umpteen*20 minimal impedance then I probably don't have to worry about any thumb rules.

 

[castleofargh]

 

  How "rule of thumb" is the 1:10 ratio, though? It is odd that it's exactly where the impedance of the cans drops to its lowest that we eyeball the most difference between the amps. Innerfidelity gives the output impedance of the UHA as 0.4ohm, so could it be the case that this difference (0.4 vs 0.54) at these frequencies, where the headphones drop right to the "rule of thumb" realm, might start making a difference? I'm just asking; someone with da EE skillz can weigh in on the answer.

 
Do note that the lowest impedance of the UERM from the plot above and many others is more like ~8 Ohm, so the damping factor for both amps should far exceed 1:10, unless I missed something.
 
And if you say 0.14 Ohm of output impedance makes a difference, then... what would that say about amps that have 2, 3, 4, 5, 10, 12, 20, 40 Ohm output impedance?
 
What would it say about audibility of differences in amps in general? Would all amps still sound the same now that you know this fact?
 

 
Quick note so that we can go back to the right topic at hand: this is far from just an EQ effect imposed on the headphone. It messes with the signal that's being sent more akin to a complicated DSP.
 
Here's an article on that:
http://www.innerfidelity.com/content/musings-headphone-amplifier-output-impedance
 
EQ both in hardware and in software should not work in this way, so if you ever come across this, it's either by pure accident that the system interacts in that way (synergy?), or the amp's designer (and headphone's manufacturer?) intended for that to begin with.
 
I am of the same opinion as Tyll, and that is... the acoustic dampening of the headphone would still make more of a difference than output impedance. Also, I have measured pretty much the same thing that Tyll has, and that is... output impedance really doesn't give much of a difference when the variation is small (0.1 Ohm is very very small change), and that's why I do not think the cause of the difference is due to output impedance. But who knows, I may just be on to the wrong thing here, and maybe the "rule" is not 1:10 but more like 1:20, 1:30 something...
 
Last note: this "rule" was 1:8 just a while earlier. So... yeah, something to mule on.
 

 

the interest is simple in the 1/8 or more ratio . it's not an ideal value, impedance bridging should wish for a 0ohm source. but it's a compromise for efficiency and damping ratio. so I insist on the "or more" part when giving that ratio.  I'm one of those who like a clear damping for peace of mind. I don't need 1/10000, but I certainly don't mind 1/50 or more.
 
to get your voltage at one frequency you use Vfreq=V*(impedance of the headphone at that freq) / (imp headphone @ that freq + impedance of the source)
so it's easy to see that the bigger the difference between source and headphone, the smaller the impact of the source's impedance.
and we can also immediately see that if the impedance of the source is close to zero, then the fact that the headphone will have different impedances at different frequencies will have almost no effect on the resulting voltage.
it's pretty straightforward.

 

[Bill-P]

  ...now I did all that because I'm a masochist(obviously), but you realize that even with extreme IEMs very likely to be affected, the changes are still below 1db in that situation. the graph looks frightening, but I doubt many people can hear less than 1db change if not in a direct comparison.

 
Sorry for cutting the quote short.
 
But at least now we are at a point where there is a measurable difference, and then all that's left is whether it is audible or not, right?
 
God, that took pages of discussion, and a lot of back and forth. I'd almost think that most of this would have been discussed to death in here...
 
Anyway, as for audibility, this article suggests that at high levels, it may just be audible. In fact, even smaller changes might be audible:
http://wiki.dxarts.washington.edu/sandbox/groups/general/wiki/9e11b/attachments/012ef/The%20ear%20and%20the%20perception%20of%20sound%20-%20Alton%20Everest%20%28from%20The%20Master%20Handbook%20Of%20Acoustics%29.pdf?sessionID=c545bdd9aafbac931cdcb9138e309ae90c7b3578
 

 At 1 kHz, for very low levels, a 3-dB change is the least detectable by the ear, but at high levels the ear can detect a 0.25-dB change. 

 
Few may hear the difference, or many may, but... the point is, it's still (potentially) audible, right?
 

  Well that's why I said "I'm just asking". And I don't think anyone has ever said "all amps will sound the same with all headphones at all frequencies"; I would think the understood caveat is "all amps that satisfy the power requirements for a set of cans and that are well outside of any 'rule of thumb' issues with impedance sound the same." Hence why I was asking about any possible rule of thumb issues, as I would imagine there's a reason that 1:8 or 1:10 or whatever is a "rule of thumb" instead of "a law." And what I think about amps with umpteen ohms output impedance is that if my headphones have umpteen*20 minimal impedance then I probably don't have to worry about any thumb rules.

 
Well, as castleofargh pointed out for me... (sorry, I did not want to be the only one trying to explain everything in this thread)
 
1:10 seems to apply somewhat to the Leckerton UHA-6S Mk.II.
 
It doesn't quite apply with the O2, so there are 3 potential explanations that I can see here (please feel free to add more if you think of anything else):
 
1) The O2's doing something "wrong". Hm... I'd say... good luck arguing this with its author.
 
2) The O2's published specs on JDS Labs is wrong and they changed something inside, which... would violate the license of the O2 (which does exhibit modifying or making changes to its schematic) and thus make all of their O2 amp business pretty much illegal. Hm... probably does not fly either.
 
3) 1:10 doesn't apply. If there is any "rule", it's now 1:22 or something to that effect.
 
4) Voodoo

 

[Head Injury]

   
1) The O2's doing something "wrong". Hm... I'd say... good luck arguing this with its author.  
2) The O2's published specs on JDS Labs is wrong and they changed something inside, which... would violate the license of the O2 (which does exhibit modifying or making changes to its schematic) and thus make all of their O2 amp business pretty much illegal. Hm... probably does not fly either.
 
3) 1:10 doesn't apply. If there is any "rule", it's now 1:22 or something to that effect.
 
4) Voodoo

1. It's not doing anything wrong. Running an estimate on the numbers quickly, the O2 in the graphs matches an output impedance of about 0.6 ohms, which is close to spec.
 
2. The graph is about what I would expect to see from an output impedance around 0.5 ohms, so it matches spec.
 
3. 1:10 (usually 1:8 AFAIK) was never a real rule. It was a suggestion. The actual ratio needed depends greatly on the headphone. Planars, for example, can get by with very large output impedance amps because their impedance curve is very flat. On the other hand, the HD598 may experience audible changes from a ratio of 1:10, because of its very large resonant peak in the mid-bass. The 1:10 rule breaks apart completely with multi-BA IEMs like the UERM, because their crossovers create large variances in impedance.
 
4. No voodoo, just math. The difference between the O2 and the Leckerton here is this particular Leckerton must have a lower output impedance than the stated specs (I'd estimate it at about 0.2 ohms).
 
I can run you through the equations to determine frequency response changes from output impedance, if you want.

 

[Bill-P]

 
1. It's not doing anything wrong. Running an estimate on the numbers quickly, the O2 in the graphs matches an output impedance of about 0.6 ohms, which is close to spec.
 
2. The graph is about what I would expect to see from an output impedance around 0.5 ohms, so it matches spec.
 
3. 1:10 (usually 1:8 AFAIK) was never a real rule. It was a suggestion. The actual ratio needed depends greatly on the headphone. Planars, for example, can get by with very large output impedance amps because their impedance curve is very flat. On the other hand, the HD598 may experience audible changes from a ratio of 1:10, because of its very large resonant peak in the mid-bass. The 1:10 rule breaks apart completely with multi-BA IEMs like the UERM, because their crossovers create large variances in impedance.
 
4. No voodoo, just math. The difference between the O2 and the Leckerton here is this particular Leckerton must have a lower output impedance than the stated specs (I'd estimate it at about 0.2 ohms).
 
I can run you through the equations to determine frequency response changes from output impedance, if you want.

1) castleofargh already did the analysis (I haven't looked it over in details), and I don't think it correlates with 0.6 Ohm. But if that's the case, then you're saying a 0.1 Ohm change in output impedance would still cause a difference. Also that castleofargh made an error somewhere in his analysis, in which case, you may want to point it out to him.
 
2) UHA-6S Mk.II also has 0.5 Ohm impedance from specs. Or more like <0.5 Ohm from specs, but we are not given the correct value.
 
3) Yeah, I was just messing with him. Please notice how he was asking about this.
 
4) I'm also messing around here.
 
Seriously, does everything I say in here always have to be factually correct, proper, and analyzed like it's a statement in a court?

 

[castleofargh]

well nobody here I would guess pretends that 2 stuff can be perfectly identical. if the point was to say that there are differences, then sure there always are measurable differences(well except for digital copies ^_^).
you can go with it on cables, headphones, DACs, or rocks. when someone here says that 2 amps should sound the same it clearly means audibly the same for a random human. having 2 amps with the same impedance, a ruler flat FR from 20hz to 20khz and below -80db distortions is not at all an impossible feat. if they both are in the clear to drive a given headphone, then they will both very much sound the same once volume matched. there won't be any mystical phenomenon unknown to science that would be responsible for audible differences.
 
about audible differences, we count 0.1db margin as good for volume matching. so even if we say that 0.2db can be heard, that's under certain circumstances. it has nothing to do with giving a guy a source, then the next day giving him the same with a 0.6db change somewhere and expecting him to notice. I know that when I'm trying to set volume levels with the switch (as a game, because now I measure it with my soundcard instead). I have no problem getting less than 0.5db error and most of the time that's because the source doesn't have precise enough steps. so with instant switching I very much agree that 0.2 or 0.3 shouldn't be impossible. they won't matter one bit but you can hear the change. now if I have to unplug my IEM to go from one source to the other one, it will take 3seconds, + the noise from plugging the jack. I now have a real hard time getting a 1db precision. that's what I was talking about the 2 amps and a 1db difference likely to go unnoticed.
real life situation, not golden hear guy with switch in perfect silence.
 
 
on a personal level now, I have a O2 and a UHA760 and I couldn't/can't really tell them apart unless I go for max output. I still don't know what leckerton was used in the graph(4? 6?), but at least I expect both signatures to be close to ruler flat from 20hz to 20khz, so again I can only see impedance as a motive for those graphs. and the shape of the deviations once again agrees with the idea.
 
 
edit: yeah but what I did was take MRO impedance response and go with the old school DC signal game. I could have saved time by looking at the differences on the graph with all the IEMs instead ^_^. that can give an idea of the actual values used instead of me going with theory and look if it fits(and very possibly with an error here or there, I didn't double check anything or thought too much about it).

 

[jcx]

psychoacoustics also has bearing - just how much frequency deviation can be heard: http://djcarlst.provide.net/abx_crit.htm

 

[Head Injury]

Quote:

 
1) castleofargh already did the analysis (I haven't looked it over in details), and I don't think it correlates with 0.6 Ohm. But if that's the case, then you're saying a 0.1 Ohm change in output impedance would still cause a difference. Also that castleofargh made an error somewhere in his analysis, in which case, you may want to point it out to him.

I was going by the impedance graph you provided, which apparently is not the UERM

 
I assumed 0.6 ohm output impedance, with 25 ohm impedance at 100 Hz, 7 ohm impedance at 7 kHz.
 
(7 / 7.6) / (25 / 25.6) = 0.94 which is -0.54 dB difference. 0.65 ohm output impedance would be closer to the real value, but I was moving quickly. It's moot anyway since it's the wrong impedance curve.
 
His math's right.
 
Appears to still be true than the Leckerton comes out to about 0.2 ohm output impedance with the correct UERM impedance curve.

 

[RRod]

1) castleofargh already did the analysis (I haven't looked it over in details), and I don't think it correlates with 0.6 Ohm. But if that's the case, then you're saying a 0.1 Ohm change in output impedance would still cause a difference. Also that castleofargh made an error somewhere in his analysis, in which case, you may want to point it out to him.

2) UHA-6S Mk.II also has 0.5 Ohm impedance from specs. Or more like <0.5 Ohm from specs, but we are not given the correct value.

3) Yeah, I was just messing with him. Please notice how he was asking about this.

4) I'm also messing around here.

Seriously, does everything I say in here always have to be factually correct, proper, and analyzed like it's a statement in a court?

Did I phrase my question badly?

 

[Bill-P]

Did I phrase my question badly?

 
No, I was just being mean and evil. Sorry! 

 
Honestly, though, it's not a jab at you. I personally admit to having heard no difference between certain amplifiers even with headphones where such differences should have been obvious (and I do listen at very loud volumes), but then, I also heard differences where there should be none.
 
If only all headphones are planar magnetic. That would be so nice.
 

  I was going by the impedance graph you provided, which apparently is not the UERM 

 
I assumed 0.6 ohm output impedance, with 25 ohm impedance at 100 Hz, 7 ohm impedance at 7 kHz.
 
(7 / 7.6) / (25 / 25.6) = 0.94 which is -0.54 dB difference. 0.65 ohm output impedance would be closer to the real value, but I was moving quickly. It's moot anyway since it's the wrong impedance curve.
 
His math's right.

Yep. That was my bad. 

 
The headache caused by having to calculate all of that and selecting the right amp ultimately pushed me away from trying higher-end IEMs, and the worst thing was that the UERM was one of those IEMs that I would have ended up owning if not for its difficulty in terms of amplification requirements.
 
So now I have orthos for desktop. Flat impedance, as you said, and I could put together my own cheap-ish but super powerful amplifier to drive it, and it won't even exhibit a single problem since the flat impedance doesn't cause anything within the amp to act up.
 
And now I'm thinking of making my own planar magnetic headphone for portable use. I'm just too in love with the way they "sound" subjectively.

 

[Rajikaru]

I've always thought that if a theoretical comet hit the theoretical 'audiophile' planet, it's the guys listening to music, and perfectly enjoying it through their $99 FiiO X1s* with built-in EQ function and $120 Audio Technica M50s who will "inherit the earth". 

Most will eventually get the Darwin award due to incurable Pedantry.

*If they listen to a hard-to drive orthodynamic, they should use their line-out to an Objective 2.