A speaker system includes an enclosure having a port from which a duct extends into the interior of the enclosure. A board having a smaller area than the cross-sectional area of at least the exit of the duct is mounted to block the port except a slight slit defined by the entire circumferential edge of the board and the opposed inner wall of the duct, so that the slight slit serves as a pressure duct whereas the remainder of the duct serves as a guide duct.