Can I ask how 10mV was decided as the safe limit? I'm following some of what is being discussed here, but I'm quite new to the concepts.
I understand that an increase in current results in an increase in heat and that there is a point where the conductor will break down. I've seen shots of Grado drivers, and the wiring from the cable to the magnet is extremely thin - not much beyond human hair thickness perhaps.
Though one thing which is confusing me about this (and this is really getting down to basics), is that I've read higher impedance headphones are less susceptible to damage from DC offset. I understand higher impedance headphones need higher voltage to drive - to overcome their higher resistance (impedance) - but since (I think) we're saying too much current through a very fine conductor is the ultimate cause of DC offset damage, I'm struggling to understand, therefore, where voltage values come into the equation? Surely it would be better to specify dangerous current levels, thus negating the fact headphones of different impedances have differing levels of susceptibility to DC offset voltages. I hope this makes some sense!
To take a real world example, I measured the DC offset from my iphone 4 line out recently and it was 10mV. I've got it hooked up to my AMB Mini³, which has no decoupling caps, and at listening levels the DC offset is amplified to 50mV by the mini³. I'm driving Sennheiser HD 25-1 II, which are 70ohm. (By the way, I couldn't measure the DC offset from the iphone with music playing as it confused my DMM - I've read this is a common limitation, but for a few seconds after pausing the music my DMM read 10mV.) Apologies if this last paragraph is getting a bit off topic.
Edited by jr41 - 4/29/11 at 3:40am