PURPOSE: To improve the acoustic pressure in the vicinity of a low band threshold frequency by constituting the subject structure so that acoustic pressure radiated from a duct part of a phase inversion type cabinet, and acoustic pressure radiated from an acoustic filter of the front side of a loudspeaker unit are added together.

CONSTITUTION: On the front side of a loudspeaker unit 1, a low-pass acoustic filter 6 is provided, and also, on the rear side of the loudspeaker unit 1, a phase inversion type cabinet 7 is installed. Accordingly, acoustic pressure radiated from a duct part 8 of the phase inversion type cabinet 7, and acoustic pressure radiated from the acoustic filter 6 on the front side of the loudspeaker unit 1 are added together. In such a way, an acoustic pressure level in the vicinity of a low band threshold frequency rises.