Thanks a lot for the explanation Alex. A few questions: 1. 85db/mw is with the impedance box attached right? From what Danny told me, for the same power the headphone should get at least 20dB louder with without the impedance box. 2. What's the F0 of these drivers? And since they don't need any enclosure, what's the lowest register they can go in an open air environment under +/-3dB threshold?