The Sennheiser CX 300-II Precision are white in-ear headphones that are designed to use with an array of portable devices. This includes cell phones, iPods, and generic MP3 players. The headphones can also be connected to any device that has a headphone jack. These Sennheiser headphones provide noise isolation, which blocks out any outside noise. This is useful for busy locations like such as the gym or subway. It allows the user to filter out any background noise and listen to their favorite music. The Sennheiser headphones are in-ear headphones that come with small, medium, and large ear cushions that are designed to fit an array of ear canal sizes. These Sennheiser headphones use 5 mm drivers, which provide dynamic bass response and 19 Hz to 21 kHz frequency response, which aids in accurate sound reproduction. The Sennheiser CX 300-II Precision in-ear headphones offer 113 dB/mW of sensitivity and provide 16-Ohm impedance of extreme power. The Sennheiser headphones are lightweight and portable, which makes them easy to travel with.