Originally developed for professional musicians, the E2c combines Dynamic MicroDriver speaker technology with a sound isolating design to deliver rich, full-range sound while blocking outside noise, ideal for enhancing your listening experience with portable MP3, DVD and CD players as well as all other audio sources. The E2c's in ear design works like an earplug to block background noise naturally. This enables you to listen comfortably at lower volumes, even in loud environments. And unlike bulky headphones utilizing active noise cancellation technology, no artifacts are introduced into your listening experience. Sound isolating earphones are also much smaller and don't require batteries.The E2c's speakers are constructed with studio-grade components, producing outstanding audio clarity that allows you to hear your music like never before. Because every ear is different, E2c Earphones come with three pairs (small, medium, large) of disposable Foam Sleeves, and three pairs (small, medium, large) of Flex Sleeves to ensure the ideal personalized fit. The soft, flexible sleeves in the Fit Kit gently contour the inside of the ear for a comfortable, secure fit so that the earphones don't fall out while you're exercising.