Overview: The Shure BLX14/P31 Headworn Wireless Microphone System consists of the BLX4 Wireless Receiver, and the PGA31 Headworn Microphone with the BLX1 bodypack transmitter. You can operate up to 12 compatible systems per frequency band (depending upon your region). The system operates on the H9 frequency band (512 to 542 MHz), and has a transmitting range of approximately 300 feet.