I've been using my recording studio headphones (Sony 7406's) and they sound awesome, all the way to the last notch, before full volume on the Droid... at FULL volume, they crack very slightly, on the bass beat (mainly in the left ear, which is strange).
No, nothing like that. On full volume, on my fairly cheap Philips noise cancelling phones, you get just a taste of the phones being overdriven. Nothing like that on the Grado 125's. I have some Sony's around here somewhere, but have not tried them yet.
I figured it had something to do with headroom or impedance mis-matches.
Impedance mismatch isn't a real problem at audio frequencies anyway, unless you're way off (eg, trying to drive a 4 ohm load with a driver intended for 100 ohm phones... you don't get much volume. But none of the classical impedance mismatch effects (reflections, etc)... the distance is just too short.
But impedance differences... that can very easily account for difference in volume vs. distortion between different phones. Earbuds range from 16 ohms to over 100, but 32 ohms is pretty standard for most phones (all Grados are 32 ohms, not sure about Sonys). But if you're hearing the same thing in multiple sets, I have to blame the DROID.
I may check out an in-line headphone amp...so I can leave Droid at 1 notch below full and amp on like 2 or 3.
I have been thinking of this, too. I only recently started using my DROID for audio, but it's one expected function... I had a 16GB SDHC card in my old Treo for the same reasons. When you look at big power draws in a mobile device, you have things like "screen" and "transmitter", but audio is a fairly big one, too.. you can easily drop 200mW on a headphone amplifier, if not more. So adding a headphone amp and dropping the output levels will help. Also, you never get the top fidelity at full volume... I notice on mine, on the last volume notch, the background noise seems to rise more than the signal.
Another option are Bluetooth headphones. Some experimentation would be needed, but it's quite possible that uses less power than analog phones. Class 3 Bluetooth (up to 10m, the usual sort you get for PAN applications from a mobile device) is only using 1mW transmit power. Of course, there's other computational overhead, compressing the audio and all, but it's an interesting trade-off... assuming all BT headphones aren't drek, of course.
$20