Sony MDR-7509 Professional Studio Monitor Stereo Headphone MDR-7509 For critical applications - Extremely wide freqiuency response, especially for monitoring of bass-heavy material. Extremely rugged design 50mm Driver Unit - For clear, high quality sound reproduction, extreme power handlking and superior bass response Circum-aural, Closed-Ear design - Covers the entire ear for extreme comfort and tight acoustic seal Stereo Unimatch(R) Plug - Compatible with 1/4 and 1/8 headphone connector plugs