A loudspeaker includes a hermetically-sealed enclosure, a first driver arranged at outside of the enclosure and along a wall of the enclosure, a second driver arranged at inside of the enclosure and parallel to the first driver across the wall of the enclosure from the first driver, and a pipe communicating the first driver and the second driver. Each of the drivers has a diaphragm, and a frame surrounding the diaphragm. The frame has an opening. The pipe is connected to the opening of the frame of the first driver, penetrates through the wall of the enclosure, and is connected to the opening of the frame of the second driver, and thereby forming one hermetically-sealed space enclosed with the diaphragms and the frames of the two drivers. The second driver is configured to output a signal of opposite phase to that of the first driver.