1. Concerning a curve passing through those points (in a theater, concert-room, etc.) at which a speaker or performer may be heard equally well: Terry always chooses the most isacoustic seat in the auditorium so she can hear the speakers.
2. A reference to the equal intensity of sound: The natural acoustics of the outdoor amphitheater provided balanced isacoustic music.
3. In seismology, pertaining to a line (imaginary or on a map) connecting places where an equal percentage of observers hear the sound of an earthquake: The seismologists at three universities realized that their institutions were situated on an isacoustic line meaning that they each could hear quakes equally well when they occurred.