An ear canal earpiece comprising an electroacoustic sound transducer, a first sound guide unit for guiding the sound from the electroacoustic sound transducer, an ear mould unit which comprises: a second sound guide unit for prolonging the first sound guide unit, and a third sound guide unit which is embodied as otoplastic means and surrounds the second sound guide unit and is adapted to guide sound further into the ear canal of a user, wherein an outside contour of the third sound guide unit is matched to an inside contour of an ear canal of a user, and a sound wall which is acoustically of a substantially sealing nature and is arranged in the region of the second sound guide unit, wherein the sound wall extends between the second and third sound guide units (130, 140) and provides an acoustic termination for the acoustically effective region of the third sound guide unit and acoustically separates a front side from the rear side of the electroacoustic transducer, wherein the sound wall is arranged at the end of the third sound guide unit remote from the ear, wherein the ear mould unit is removable together with the second and third sound guide unit (130, 140) from the first sound guide unit, wherein an inner diameter of the third sound guide unit is bigger than an inner diameter of the second sound guide unit, wherein the third sound guide unit comprises a reduced wall thickness for increasing the acoustically effective cross section and a minimum wall thickness for providing a certain mechanical stability, wherein in the entire acoustically effective region of the third sound guide unit, a ratio of the acoustically effective cross section to a total cross sectional area of the outside contour of the third sound guide unit is everywhere greater than 40%. an electroacoustic sound transducer, a first sound guide unit for guiding the sound from the electroacoustic sound transducer, an ear mould unit which comprises: a second sound guide unit for prolonging the first sound guide unit, and a third sound guide unit which is embodied as otoplastic means and surrounds the second sound guide unit and is adapted to guide sound further into the ear canal of a user, wherein an outside contour of the third sound guide unit is matched to an inside contour of an ear canal of a user, and a sound wall which is acoustically of a substantially sealing nature and is arranged in the region of the second sound guide unit, wherein the sound wall extends between the second and third sound guide units (130, 140) and provides an acoustic termination for the acoustically effective region of the third sound guide unit and acoustically separates a front side from the rear side of the electroacoustic transducer, wherein the sound wall is arranged at the end of the third sound guide unit remote from the ear, wherein the ear mould unit is removable together with the second and third sound guide unit (130, 140) from the first sound guide unit, wherein an inner diameter of the third sound guide unit is bigger than an inner diameter of the second sound guide unit, wherein the third sound guide unit comprises a reduced wall thickness for increasing the acoustically effective cross section and a minimum wall thickness for providing a certain mechanical stability, wherein in the entire acoustically effective region of the third sound guide unit, a ratio of the acoustically effective cross section to a total cross sectional area of the outside contour of the third sound guide unit is everywhere greater than 40%. a second sound guide unit for prolonging the first sound guide unit, and a third sound guide unit which is embodied as otoplastic means and surrounds the second sound guide unit and is adapted to guide sound further into the ear canal of a user, wherein an outside contour of the third sound guide unit is matched to an inside contour of an ear canal of a user, and a sound wall which is acoustically of a substantially sealing nature and is arranged in the region of the second sound guide unit, wherein the sound wall extends between the second and third sound guide units (130, 140) and provides an acoustic termination for the acoustically effective region of the third sound guide unit and acoustically separates a front side from the rear side of the electroacoustic transducer, wherein the sound wall is arranged at the end of the third sound guide unit remote from the ear, wherein the ear mould unit is removable together with the second and third sound guide unit (130, 140) from the first sound guide unit, wherein an inner diameter of the third sound guide unit is bigger than an inner diameter of the second sound guide unit, wherein the third sound guide unit comprises a reduced wall thickness for increasing the acoustically effective cross section and a minimum wall thickness for providing a certain mechanical stability, wherein in the entire acoustically effective region of the third sound guide unit, a ratio of the acoustically effective cross section to a total cross sectional area of the outside contour of the third sound guide unit is everywhere greater than 40%.