Those headphones seems to have been "designed for DVD audio". If you look at the following page, it seems panasonic quotes the frequency response of their "DVD-Audio-Ready" stuff at -16dB.http://www.panasonic.sk/dvd_player/ready/
For instance, their SB-M800 speakers are "3-Way, 5-Speaker Technics D.D.D. (Dual Dynamic Drive)", having a "Super Graphite dome tweeter achieves high frequency extension up to 100kHz (-16dB)". All sounds very exciting, don't you think
So i think it's safe to assume the 3Hz-100kHz (!!!) for those cans is at -16dB as well.
Oh, BTW, I asked members of the Troklian star fleet council, and their hearing is receptive to frequencies of 0.2Hz - 250kHz (-102dB)