Koss CC_01 isolating in-ear headphones feature a unique, custom fit experience. Rotate the dial and the ear cushion expands to provide perfect fitting in-ear headphones with great sound. It's an entirely new state-of-the-art ergonomic and acoustic design. Koss in-ear headphones are designed to produce a perfect seal. This seal allows the variable matched transducer to directly couple with the eardrum. This direct response system means greater accuracy and efficiency across the entire frequency response range. The transducer in the CC_01 in-ear headphones features a custom-ported design to enhance frequency response and deliver deep bass. It’s cross-matched for balance across the entire musical spectrum.