Abstract: This invention provides a kind of acoustic structure that uses passive diaphragm unit, it includes speaker unit, passive diaphragm unit, radiant tube; said passive diaphragm unit is located at the back of the cone of said speaker unit; the speaker unit has radiant tube on the sides; the said radiant tube end which is exposed in the air is located at the periphery of the cone of said speaker unit. It has the same orientation as the speaker unit; the said passive diaphragm unit vibrates when it is driven by the said speaker unit, the sound waves produced by the vibration of the said passive diaphragm unit are emitted by the radiant tube and radiant opening, and share the similar vocal point of the said speaker unit. With this, the sound effect of the full range sound is almost identical to the sound point sources, it also reduces the phase difference between the sound effects produced by the cone of speaker unit and the passive diaphragm unit, further enhanced the sound positioning feature.