That's 2Vrms for 105dB peak, more than enough for normal listening levels even with moderate EQ.
I had a 250 Ohm DT 880 a long time myself and was never even close to that.
With severely reduced hearing or extreme EQ a little more power might be necessary.
I might measure power required for the 250 Ohm DT 990 later today, I can measure current into a specific resistance (doesn't make much of a difference with the Atom since it's not current limited), but don't have a proper SPL meter unfortunately, so subjective impressions will have to do.
So:
On my Atom with E30 input (about 2.1Vrms) and a DT 990 250 Ohms with worn out pads (might be a little quieter with decent pads) listening to Dire Straits - Lady Writer the pot positions:
10:00 - decently loud level, about the max I`d use for normal listening
12:00 - loud, more than I`d want to expose my ears to for extended periods of time, wouldn't do that for more than half a song maybe.
14:00 - too loud, very unpleasant, can't stand it for more than a few seconds.
My ears are fairly decent still. Older people might require higher volumes, but if 14:00 isn't enough I`d wager to say the person wouldn't cope well without a hearing aid in day to day life.
So let's see what the voltages are, I don't know yet as of writing this sentence but it has to be way less than 2Vrms.
I will measure the current with a 1kHz 0dB sine wave, wich gives us a higher and constant voltage compared to playing music.
Measured current // calculated voltages (in 218.6Ohm resistance):
10:00 - 0.64mA // 0,140V
12:00 - 1.16mA // 0,254V
14:00 - 3.90mA // 0,853V [the song used jumps around 1mA at this level, so a lot quieter than a sine wave].
So the voltage is not gonna be the problem. Current limiting might be at very high listening levels with very dynamic music with lots of bass, but I don't think that would really come into play.
The EVO4 will not do well with low impedance and low sensitivity headphones however, something like the AKG K712 Pro will make it clip at moderate listening levels I'm sure.
