Abstract: A modular acoustic sound system for a room for two-way conversations without the need for switching. The system includes pairs of microphones each connected to a phase shifter so that in-phase signals inputted to the microphone pair are shifted 180.degree. apart. The out-of-phase signals are input to a summing circuit having an amplified output which drives a plurality of loudspeakers. A portion of the audible loudspeaker outputs enters the microphone pair, is phase shifted, and cancelled out in the summing amplifier. Any number of loudspeaker/microphone pairs operate in the system and any microphone may be spoken into to drive every loudspeaker.