One critical factor is I want the phones to sound loud enough when listening on my iPod. On Oppo's page they say "The OPPO PM-3 has a sensitivity of 102 dB, which allows it to be easily driven with mobile devices." So is it this sensitivity rating that indicates the headphones are suitable for mobile device listening without additional amplification? How do I read and understand what this number means? Shure lists the sensitivity of their SRH1540 as 99 dB, is that in the range that compares with Oppo's claims for the PM-3?