[TobaccoRoad]

I tried searching, but the more I read, more confusing I get. Is there a certain formula using impedance and sensitivity to figure out how loud the headphones are? For example:
 
Denon D1001 = 32 ohm, 130dB/mW
Denon D2000 = 25 ohm, 106dB/mW
Sennheiser HD595 = 50 ohm, 112dB/V
 
My amp's specs (Nuforce HDP):
 

1. 288mW rms @ 30 Ohm
2. 210mW rms @ 120 Ohm
3. 152mW rms @ 300 Ohm
4. 123mW rms @ 500 Ohm
5. 96mW rms @ 600 Ohm
6. 59mW rms @ 1200 Ohm
7. 43mW rms @ 1700 Ohm
8. 35mW rms @ 2000 Ohm

 
To me, HD595 is the loudest given the same volume followed by D1001 then D2000, but we're all getting mixed opinions here. Also this could be the result of different frequency response (more midrange = louder?), so nothing has been confirmed so far. Can anyone tell me which headphones are supposed to be the loudest given the specs?

 

[atothex]

Higher sensitivity number = louder.

 

[TobaccoRoad]

But why isn't D1001 louder than HD595 when its sensitivity is much higher?

 

[atothex]

If you look carefully at the specs, you see that the units are different: dB/mW vs dB/V. Sennheiser is trying to trick you. I think the dB/mW is technically efficiency.

 

[TobaccoRoad]

I know, but if you convert V to mW the number actually gets LOWER. This absolutely makes no sense.