Koss stereo in ear headphone the plug the koss plug revolutionized the world of in ear headphones a first of its kind these are stereo noise isolating in ear headphones that deliver the kind of accurate acoustical reproduction and isolation typically found in high end closed style high fidelity headphones a dynamic element positioned just outside the ear connects to a tubular port structure that inserts into a soft expandable cushion the soft foam cushion expands for a custom comfort