Does headphone impedance matter?

it depends on the amp. the most accurate answer anyone can give with the information at hand.

direct coupled SS amps probably wont have too much trouble putting the noise into 25ohms.

cap coupled tube amps do depend on many factors, but unless its a flea-powered amp it should also go.

cap coupled SS amps get quite interesting indeed. the potential to drive alllll the power a headphone will ever need is there, but there may be issues with the cap being slightly small. the cap coupled tube amp is somewhat less sensitive to this because of how the tubes react to the increasing apparent impedance of the load as the frequency decreases.

transformer coupled tube amps are a VERY different story. if they follow the trend to operate a small loudspeaker transformer with the heapdhone running off of an 8-ohm output tap at a very conservative power level they should do nicely. if they are of the less comon type which runs the heapdhone off of a transformer with a 600-ohm output tap you are fuxored.

There are amps, such as the XM5, that have switchable output impedance (XM5 adds 75ohms). That should help with low impedance headphones. There are also adapters you can buy for amps that don't have a switch.

Yes, it is important.

The way it works is that you need to consider how closely the output impedance of an amp matches the impedance of the headphones. This shows how much power is transferred from the amp to the headphones. The closer the two match, the better the power is transferred.

Once you have that figured, you look at the power output of the amp and the sensitivity of the headphones. The amount of power delivered to the headphones tells you how loud the headphones will get depending on how sensitive they are to power.

Keep in mind that impedance alone does not tell you how difficult a pair of headphones is to drive. Some with a low impedance, like Grados, are sensitive. So if less power is transferred to Grados, it doesn't matter as much because they're efficient and easy to drive.

don't listen to nikongod, he is disgusting. i have seen what he can do. the denon probably require a heap of voltage to sustain all signals well within the bounds of 25 ohm. perhaps a grado amp would work well with the denon as they too have very hard to drive low ohm phones other than just volume.

Which ones are hard to drive again? Low ohm like the 25 ohm Dennons? Or high ohm like the 300 ohm Senns?

Tim

the meier amps (with the exception of his tubes if i am not mistaken) are all directly coupled SS amps. they should provide adequate power unless you want to listen REALLY loud.

the woo, is also a STRONG contender.

i do tend to disagree with uncle eric's statement on the output impedance of the amp matching the impedance of the headphone. you generally want the output impedance of the amp FAR less than the impedance of the headphone. this is something of a nit-pickiers point. i have LOVED low impedance heapdhones from sources with fairly high output impedances. as long as you dont give something else up, lower output impedance is better.

so which of my amps and modifications has been your favorite?

so far i will say that my favorite was the MPX3 i rebuilt, and tweaked. it got alarmingly close to the supra and in some ways bested it. if my empty wallet had any say in the matter the mpx3 would have stayed and the supra gone. i would only be a little sad.

my second favorite was the zhaolu. I have never heard a digital source to match it. this is not to say that i have not tried. i HOPE that the TPA opus (cod) will win in its battle with the zhaolu, but if not i wont be disapointed: happy that i put both together. the warrior who beats his closest adversary should feel no joy, only sorrow. with time and effort the adversary could have been a valuable teacher. regardless of who the last man standing is the battle will surely be impressive.
perhaps i made an inaccurate statement in my posting above. please find it. when you do, kindly call me out. i'l give you a demonstration now.

low impedance headphones dont need a particularly high voltage swing to drive them, they need current.

bonus point to my comment: i stated a generally accepted fact!

if the headphones needed a solid voltage swing with little current (a 300 ohm headphone comes to mind, as an example) then an OTL tube amp is an IDEAL solution in every respect. the ability to swing absurdly high voltage is there and the currents that will be used are nominal.
aah, i built one of those. well, one wasnt enough so i actually built 2 and run them balanced: its at least twice as good theres twice as many parts and solder joints.... mild mods have been done of course mostly to reduce the gain to account for the balanced drive and different brand input caps.

i have not run my d5k off of the balanced mahogany amp as its still wired single ended. i imagine it will be adequate with regards to power delivery (it is after all a direct coupled SS amp...) but im not sure if the synergy will be there. with john grado headphones (rs-1, sr-325, dt-125 upgrado) the clone sings. with joe's cans (hp-1000, my sr-200 is also wired single ended) it dosnt do as well as the melos eargasmatron. regardless, when i decide which method i will use to get the denons balanced (if i even do, i enjoy them so well single ended) i will try it out. i cant help but be curious about these things.

while the mahogany amp drives certain grados better than it has any right to (even considering NEW prices) i am not so sure it does so well for the other headphones. the synergy really isnt there.