The MX 55 VC Street offering a slightly better frequency response at 17 to 21,000 Hz. The major difference between the MX 51 and the MX 55 is the style. The MX 55 offers the twist to fit style of earbuds. The earbud design of the MX 51 Street is ergonomic and follows the standard model. Created for use with your MP3, CD, DVD, MD player and portable gaming system, they have a 2 year warranty. The earphones come with a symmetrical cable and everything fits into the carrying case. The mini-jack plug is 3.5mm and is at a right angle.