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 fit with every listening experience. It also improves isolation, plugging out ambient sounds, and enhances deep bass and treble clarity.
Koss's miniature portable earphone, affectionately dubbed "The Plug," makes use of an ear-cushion material (similar to that used in sound-blocking earplugs) that slowly expands in your ear canal to provide a custom fit and maximum sonic isolation from external noises. A detachable, extrawide headband makes these Koss-termed "stereophones" easy to carry or store.
For accurate sound reproduction, these earbud-style headphones are made with oxygen-free copper voice coils and neodymium iron boron magnets. You can enjoy them with either a portable or home audio device, since both 0.125-inch and 0.25-inch adapter jacks are included.
"The Plug" weighs a mere quarter ounce and has a frequency response rated at an impressive 16 to 23,000 Hz (though its unlikely you'll hear bass output anywhere close to what you'd get from a similarly rated loudspeaker!).
Impedance is 16 ohms, with less than a 0.3 percent distortion and reasonably high sensitivity of 112 dB SPL/1 mW.