An acoustic system includes: a first terminal device including a first-terminal sound emitting unit, an earhole sound collecting unit configured to collect earhole echo sound, and a first-terminal control unit configured to perform authentication between the first terminal device and a user based on the echo sound collected by the earhole sound collecting unit; an onboard device including an onboard-device sound emitting unit and an onboard-device control unit configured to perform authentication between the onboard device and the user based on communication with the first terminal device; and a second terminal device includes a second-terminal control unit configured to set a destination of sound data to one of the first terminal device and the onboard device when the onboard-device control unit detects that a predetermined condition including a condition that the user has been authenticated is satisfied.