I am not really a sound science type, as I don't understand these things well, but I thought I would ask here if anyone knows.
 
We are all familiar with impedance matching.  For example with my Denon D2000 (25 ohms) I would want to find an amp that has an output impedance of 3 ohms or less.  But what about current matching?  Is there any way to know the most effective amount of current or voltage needed to drive a certain pair of headphones to their best state of sound?  Could we look at sensitivity or something and determine how much minimum current our particular headphones require in order to work as the manufacturer intended?
 
Sorry if this doesn't make sense at all.

Do a google search for NwAvGuy 'More Power'. It explains this stuff pretty well and has math formulas to calculate this stuff. IIRC somewhere in these forums there is a thread about this stuff too, just can't remember the name of the thread :/
 
But anyways D2000 is really easy to drive. It needs 3mW, 0.25Vrms and 10mA into 25ohms to get 110dBSPL. So no need for an amp.
 
If your source is phone or mp3 player then there is no need for an DAC either. If your source is PC then some could argue that PC's tend to have not so great DACs, so there might be a small improvement in sound with external DAC. 

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Originally Posted by haejuk /img/forum/go_quote.gif
 
[snip]
 
Is there any way to know the most effective amount of current or voltage needed to drive a certain pair of headphones to their best state of sound?  Could we look at sensitivity or something and determine how much minimum current our particular headphones require in order to work as the manufacturer intended?
 
Sorry if this doesn't make sense at all.

Click to expand...

 
"Most effective amount of current or voltage" doesn't really make much sense.  There's not really anything the manufacturer intends, except for you to not blow out the headphones by feeding it way too much power.  For all audiophile-grade headphones, if you're wearing them, they'll be extremely loud (painful probably) by the time you exceed the max power rating, so that's not really a practical issue.
 
The more voltage applied to the headphones, the louder they will play.  The current is the voltage divided by the impedance of the headphones, so more voltage means more current.  The power is the voltage squared divided by the impedance, so more voltage also means more power.  The sensitivity of headphones is just given by how loud the headphones sound with a given input (some list dB SPL / 1 mW power input; others list dB SPL / 1 V voltage input).
 
So as alluded to above, you can look at the sensitivity and impedance of the headphones to tell how loud they will be with any given input.  This information can help you find an amp that is sufficiently powerful enough (has the electrical design to be able to handle that amount of power into headphones of that impedance, and hopefully do so while sounding good) to play at whatever volume you think is enough.  Some less-powerful amplifiers can't actually drive less sensitive headphones to loud listening levels because the design isn't capable of any more, and some amplifiers may have issues running certain headphones at certain volumes while still sounding good.  That's pretty much all there is to it.

Cool.  Thanks very much for the answers on that one.  It kind of makes sense now.  I will re-read your posts and search some sites on it.

Take a look at the thread link below, its in this section.