Abstract: A thin loudspeaker system has at least one contoured passive radiator enclosure outside the main unit, connected with at least one loudspeaker enclosure inside the main unit through at least one transmission line. The transmission line cross-sectional shape may be a circular, rounded rectangular, ovular, elliptical or any other suitable shape. With this method the diaphragm size of the contoured passive radiator may be as large as possible, without changing the thickness of main unit. The larger-sized passive radiator diaphragm may increase the air movement and as a result may increase sound pressure level (SPL) at low frequencies. This system may reduce the thickness of audio video equipment significantly and may be useful for producing deeper bass at low frequencies with less distortion, for thin equipment such as LCD TVs, plasma TVs, thin audio hi-fi system, car loudspeaker system, and other similar systems.