Nady HP03 Closed Back Stereo Headphones These closed back studio headphones from Nady feature comfortable, heavily padded headband and earcups, 40mm drivers with a frequency range of 20 to 20,000hz. These are loud earphones with an impedance rating of 32 Ohms and a 105 dB / mw sensitivity rating. The HP03 headphones are also equipped with an on board volume control, and a 6ft cord with 3.5mm stereo plug and 1/4" (6.3mm) plug adapter.