PURPOSE: To obtain an acoustic expansion device with a good characteristics and sound quality by providing a speaker unit for high tones at the back side of a low tone speaker unit attached to a vibration panel for expansion of an acoustic wave irradiation area in the opposite direction to this, and connecting both of these speaker units oppositely.

CONSTITUTION: A speaker unit 14 for high tones is attached to the back surface of a speaker unit for low tones 4, combined with a pole piece 4b in the opposite direction to it, and the high tone acoustic wave is emitted from a cone-shaped diaphragm 14a positioned opposite to the diaphragm 4a of the speaker unit 4 for low tones through a wire netting 15. Because the direction of sound emission from the speaker unit 4 for low tones and the speaker unit 14 for high tones becomes reverse, the two are connected oppositely with a lead wire in order to match the phase.