PURPOSE: To attain efficient and sufficient low frequency reproduction by forming a pressure duct part with a narrow gap in comparison with a cross section area of a duct with nearly equal interval over the entire peripheral between a peripheral ridge of a board and an aperture inner ridge of the duct.

CONSTITUTION: A guide duct D1 and a pressure duct D2 are provided to a front buffle 2 and a board 6a is made square. A step 5a is provided to an aperture of the guide duct D1 and expanded and opened and the pressure duct D2 is formed between the expanded aperture inner ridge 5b and the peripheral ridge of the board 6a. The pressure duct D2 is formed with a narrow width and nearly equal interval over the entire peripheral of the board 6a and a proper length is adopted to the radial diameter. Thus, the pressing operation of the irradiated sound is produced effectively.