[Mr Rick]

   
Yes it is - You fiddle around with the knob (!!) until both units sound the same and there you have it : Matched to within 0.2dB
If you can't achieve that - At least one of the units is not transparent .

 
Studies have found that matching within 0.2bB is seldom if ever attainable, 1 to 3 dB is much more reasonable in a real world environment.
 
 
 
http://www.audioholics.com/room-acoustics/human-hearing-amplitude-sensitivity-part-1

 

[stv014]

  Yes it is - You fiddle around with the knob (!!) until both units sound the same and there you have it : Matched to within 0.2dB
If you can't achieve that - At least one of the units is not transparent .

 
Even if your figure of 0.2 dB is correct (which is doubtful, especially if the matching is done sighted, with music, and without the ability to switch in a fraction of a second between the amplifiers, it is not so easy to decide for sure when they sound the same; not sure where you got that number from), it is actually not good enough. There have been reports of people successfully detecting that difference in ABX tests, for example on Hydrogenaudio.
 
Now it may be argued that in theory any difference that can be detected can also be used for the purpose of level matching, but that would at best make it a rather slow process, because the same effort would have to be spent on testing each position of the volume knob at very small increments as on an actual listening test. Measuring the output voltages with the headphone load is faster, more reliable, and the required tools are cheap compared to audiophile equipment, so there is not much reason not to use that method.

 

[sonitus mirus]

   
 Measuring the output voltages with the headphone load is faster, more reliable, and the required tools are cheap compared to audiophile equipment, so there is not much reason not to use that method.

 
I have some ideas, but what would be the most efficient method to perform this measurement?
 
I have a cheap multimeter, is this adequate?  If you have the time and patience, what are the basic steps required to do this with some accuracy?

 

[bufferoverflow]

   
Studies have found that matching within 0.2bB is seldom if ever attainable, 1 to 3 dB is much more reasonable in a real world environment.
 
 
 
http://www.audioholics.com/room-acoustics/human-hearing-amplitude-sensitivity-part-1

 
From your source :
Quote:

..level differences I've been able to discern is in the range of .75 dB to 1 dB.
And :
a .25 dB detectable difference using real music just isn't plausible and the research supports that.

Anyway, you are taking what I wrote WAY to serious - I just wrote it because people always moan about how difficult it is to measure it, and use that as an excuse to not level-match at all .
It really isn't that hard, fiddle with the knobs until it sounds the same and you are done .. Or at least one of the amps is crap ..

 

[headdict]

It really isn't that hard, fiddle with the knobs until it sounds the same and you are done .. Or at least one of the amps is crap ..

...
If you do this adjustment sighted and you are biased, by this method you will just confirm your preconception that one amp is crap compared to the other.

 

[Ruben123]

Could anyone explain to me, how people often find the dynamics/dynamic range increases while using an amp and the max volume does not change (it only sounds fuller)?

If the soft instruments get louder because of the amp, but the max volume does not change (they say!), and the sound becomes fuller and tighter and go on (forgetting the impedance mismatch which could warm up the sound), how on earth gets the dynamic range bigger? It only gets smaller doesnt it. Less difference between soft-loud is smaller DR. Though reviewers seem to finder higher DR but no increase of the max volume because well only the power of the music, which the headphone needs, increases. More power to the lows yo! But not to the highs. Or something. More sound/head stage. Vocals open up. Etc. Such a magic box... a simple amplifier. My question is only about the DR though, you can ignore the rest. Or not.

Maybe some audiophile could explain this further as I might not fully understand it (English is not my native language).

 

[Dobrescu George]

Could anyone explain to me, how people often find the dynamics/dynamic range increases while using an amp and the max volume does not change (it only sounds fuller)?

If the soft instruments get louder because of the amp, but the max volume does not change (they say!), and the sound becomes fuller and tighter and go on (forgetting the impedance mismatch which could warm up the sound), how on earth gets the dynamic range bigger? It only gets smaller doesnt it. Less difference between soft-loud is smaller DR. Though reviewers seem to finder higher DR but no increase of the max volume because well only the power of the music, which the headphone needs, increases. More power to the lows yo! But not to the highs. Or something. More sound/head stage. Vocals open up. Etc. Such a magic box... a simple amplifier. My question is only about the DR though, you can ignore the rest. Or not.

Maybe some audiophile could explain this further as I might not fully understand it (English is not my native language).

different amps sound different
different pieces of equipment sound different.
 
no matter the reason. you should search for what sounds the best to you.

 

[stv014]

  I have some ideas, but what would be the most efficient method to perform this measurement?
I have a cheap multimeter, is this adequate?  If you have the time and patience, what are the basic steps required to do this with some accuracy?

 
Even a cheap multimeter can be adequate as long as it can measure AC voltage with any reasonable accuracy. It does not need to show accurate absolute levels, since it will only be used for the purpose of testing if two voltages are equal.
 
You will also need a splitter to be able to measure the output voltage of the amplifier while it is driving the headphones. This is not required if you know for sure that the output impedance of both amplifiers is at least 100 times lower than the lowest impedance of the headphones, but if you are not using >= 250 ohms headphones, that is quite often not the case. The splitter can be made DIY, or bought for a few dollars. It is easiest to use a 1xfemale to 2xmale TRS Y-splitter, but those can be somewhat difficult to find (note that many similar looking splitters are sold for use with headsets, to be able connect them to a separate microphone input and headphone output, but those are not suitable for this application). Alternatively, one could use a combination of a much more common 1xmale to 2xfemale TRS Y-splitter (1/8" and 1/4" versions can both be found easily), and a simple male TRS to male TRS or male TRS to 2xmale RCA cable. For unloaded measurements, having only the latter would be enough.
 
Make sure that there are no contact problems, and that the cables and connectors used do not have unusually high resistance (like some particularly poor quality ones do).
 
For generating a test tone, you can use freely available software like SineGen or Audacity. Some multimeters (especially cheap true RMS capable ones) have problems measuring AC voltage and current at much higher than 50-60 Hz. This can be tested by measuring the unloaded output voltage at different frequencies. But if there is no extreme drop in the measured signal level at 1 kHz compared to 60 Hz (even a decrease by a factor of 2 can be OK, as knowing the exact absolute level is not important), then 1 kHz may still be recommended, because full size dynamic headphones tend to have less reactance at 1-2 kHz than in the bass range, so there is less chance of inaccurate matching due to output impedance effects, and the low kHz range also better represents the perceived loudness.
 
There are some potential problems that can make accurate matching within an error of 0.1 dB or 1% voltage difference difficult. Especially with digital or digitally controlled volume controls, the resolution might simply not be enough to achieve that accuracy. Digital volume controls can often be adjusted in steps of 1 or at best 0.5 dB. In the case of analog volume controls, depending on the quality of the potentiometer, its taper function, and the position it is used at, it can be difficult to make sufficiently fine adjustments. Additionally, channel balance is often an issue especially with potentiometers. If at least one of the amplifiers has a balance control, it could be used to match the channel balance as well, but unfortunately analog balance controls are uncommon on headphone amplifiers. If the mismatch is relatively small but not insignificant, then it is recommended to match the overall level of the two channels, which is the sum of the squared voltages (= power), but in practice a simple average is good enough as the difference is well below 0.1 dB at 1 dB channel imbalance.
 
If the accuracy of matching the levels and channel balance cannot be made good enough, the input levels to one of the amplifiers (i.e. the presumably worse one for those worried about any quality loss) may need to be controlled externally, either with a pre-amplifier or simple passive attenuator, or using a multi-channel DAC/sound card with software upmixing and controlling the levels on one pair of channels.

 

[headdict]

@Ruben: Unless you are using very special equipment to compress or expand the dynamic range, it won't change during playback. When people think they perceive such differences, they either don't understand what DR is or are driven by their (not necessarily conscious) expectations or both. Our brains play us tricks all the time, whether we like it or not.

 

[StanD]

  different amps sound different
different pieces of equipment sound different.
 
no matter the reason. you should search for what sounds the best to you.

You left out, emotional involvement.

 

[Dobrescu George]

you cannot tell me that my cowon j3 and my fiio x5 sound the same. i cannot care less why. with x5 i can hear instruments that i cannot with j3, using sennheiser ie8, which are easy to drive. does not matter if it is loud or quiet. the test was double, quiet listening and loud listening to some songs, metal. guitars and some drums cannot be heared with j3, no matter what you do.
 
this is why one should not ever belive that equipment sounds the same. they all sound different.

 

[bufferoverflow]

...
If you do this adjustment sighted and you are biased, by this method you will just confirm your preconception that one amp is crap compared to the other.

 
Not really - But of course I am 'biased', the point here is that I know I am .. And that I expect them to sound exactly the same ...

  different amps sound different
different pieces of equipment sound different.
 
no matter the reason. you should search for what sounds the best to you.

Yes, sometimes different amps do sound different, but you are totally missing the point : They shouldn't !
Amplifiers are NOT supposed to have any 'sound-signature', neither are 'cables' nor CD-players .
ONLY transducers are 'supposed' to have any sound of their own ..
(actually they aren't supposed to either, but good luck (and MEGA-bucks) making a transducer that is 'transparent' ..
Even better luck finding a recording made for a transparent speaker-system )

 

[Dobrescu George]

   
Not really - But of course I am 'biased', the point here is that I know I am .. And that I expect them to sound exactly the same ...
Yes, sometimes different amps do sound different, but you are totally missing the point : They shouldn't !
Amplifiers are NOT supposed to have any 'sound-signature', neither are 'cables' nor CD-players .
ONLY transducers are 'supposed' to have any sound of their own ..
(actually they aren't supposed to either, but good luck (and MEGA-bucks) making a transducer that is 'transparent' ..)

okay, i totally accept that you are right. they should not. but they do not sound the same. and we should take advantage, of knowing this, not go and consider that they do. because if they would be sounding the same, everything would be pointless. i would be able to be happy with having x5 and e12, instead of hugo or idsd, and only buy headphones.

 

[headdict]

okay, i totally accept that you are right. they should not. but they do not sound the same. and we should take advantage, of knowing this, not go and consider that they do. because if they would be sounding the same, everything would be pointless. i would be able to be happy with having x5 and e12, instead of hugo or idsd, and only buy headphones.

Yes, it IS pointless and you SHOULD be happy enjoying your equipment and buy only headphones.

 

[bufferoverflow]

   they should not. but they do not sound the same. and we should take advantage, of knowing this, not go and consider that they do.
because if they would be sounding the same, everything would be pointless

OK, you still don't get it :
WHEN/IF a Hi-Fi amplifier 'sounds' 'different', it is either 'defective' (by design and/or technically) or operating outside design-specs - or both .
At this stage of technological progress, there  is no excuse for Hi-Fi amplifiers having 'a sound signature' and it doesn't even have to cost a fortune .
That is really good news, because it means -
You can stop worrying and learn how to love the music .
All serious money should be spent on source-material and 'transducers' . And 'WAF', if you have a better half