a speaker box for housing a radio speaker unit and intended for mounting within a vehicle door is formed of plastic by a monobloc molding method such as blow molding thus providing a seamless speaker box that is free from air leakage . the speaker box has an irregular configuration matching a space within the vehicle door , whereby it can be firmly secured in place maintaining maximum inner volume . the speaker box further has ribs extending across flat regions on the box thus improving its rigidity against vibration caused by sound pressure and the like .