The KSSKSC9 uses an electro/dynamic element that delivers a frequency response of 40 Hz-20 kHz. Intra-aural, or inside the ear, earbuds have been turned sideways to aim the sound directly into your ear canal for surprisingly awesome sound and kicking bass. The side firing design naturally projects the sound to your ear and also reduces the amount of physical contact to make the stereophones more comfortable. The vertical side firing design is the least isolating allowing some sound into your ear without compromising the sound quality. This innovation allows the listener to remain aware of important outside sounds while enjoying the Sound of Koss. The KSSKSC9 is big in sound, yet small in size, which allows you to store it anywhere from your pocket, briefcase or purse.