STAX SR-Lambda SR-507 Pro Headphones Earspearkers Type: push-pull electrostatic, oval sound element, open-air back type enclosure (case) Frequency response: 7 - 41,000 Hz Sound pressure sensitivity: 100dB / input 100Vr.m.s. / 1kHz Maximum sound pressure level: 118dB / 400Hz Ear pad: genuine leather (skin-touching portion)