Product Features Easy installation with no alteration fits most standard acoustic guitars with 4" (101.6 mm) diameter Fits soundholes with 3-7/8" (984mm) or 4" (101mm) diameter Flexible surround reduces "howling" in high-volume situations Integrated feedback-buster for high-volume playing Low-profile, high-impedance design needs no battery Neodymium magnet structure for exceptional string balance and sparkling acoustic clarity Output: 10' cable with 1/4" plug