The adaptor may, in theory, change the frequency response of your headphones - it may make it closer to what the Beyerdynamic engineers designed the headphones to sound like. As I said, Beyer's own headphone amp - the A1, has an output impedance of 100 ohms, wheres all these amps we have been discussing have a much lower output impedance. Just for example, looking at the impedance vs frequency plot for your headphones, I would predict that all these amps would produce less bass than the Beyer A1 amp, which in turn means that the sound you hear may not be as accurate as it would be if you were using the A1 amp, which we can assume is optimised for Beyer's headphones.
It's simple to increase the impedance, though. Just plug in that adaptor. The downside is that the maximum volume will decrease, however IMHO the STX, NFB-12, and E9 would all still have more than enough volume - even with this adaptor. (I have calculated it properly, as accurately as I can. I have assumed a 114dB peak SPL, which is very loud, and all should be able to exceed that)
Greg.
Edited by skip129 - 12/26/11 at 5:49pm
