Inter-communicating sound, amplifying and transmitting systems, comprising speakers, amplifiers, microphones, inter-connecting circuits, and energizing devices whereby conversation at either point may be heard at the other point of communication.
Inter-communicating sound, amplifying and transmitting systems, comprising speakers, amplifiers, microphones, inter-connecting circuits, and energizing devices whereby conversation at either point may be heard at the other point of communication.
Inter-communicating sound, amplifying and transmitting systems, compri...