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.