Let me add that,

Headphone A is Sennheiser HD 595

Headphone B is Hifiman HE-400

According to Inner Fidelity,

**Senn 595 requires (for 90 Db)**

0.55 Volt RMS

0.05 mW

Impedance is 55 Ohm

**Hifiman HE-400 (for 90 Db)**

.129 Volt RMS

0.33 mW

Impedance is 51 Ohm

So, evidently, Hifiman wants 4 time less voltage, and almost 7 times the wattage of the Sennheisers to produce 90 decibels. I don't understand how the Sennheisers require barely a miliwatt to reach 90 decibels. They are rated 112 dB @ 1 Volt RMS. By that figure alone, I would assume 92 dB @0.1 Volt RMS.

I am trying to get myself straightened out.