An earphone simultaneously allows high-level low-frequency sound and effective noise reduction. The earphone has a front cavity separated from ambient space The earphone has a housing having a wall separating a rear cavity with an acoustic compliance from the front cavity and from ambient space; a first diaphragm reciprocatably suspended across a first through hole in the housing wall between the front cavity and the rear cavity and adapted to be actively driven to provide the acoustic output signal; and a second diaphragm reciprocatably suspended in the housing wall between the rear cavity and ambient space where the acoustic resonant system is configured such that the resonance frequency is below 500 Hz. The second diaphragm attenuates acoustic signals entering the rear cavity from ambient space at frequencies above the resonance frequency and virtually increases the acoustic compliance of the rear cavity at frequencies below the resonance frequency.