Cables Unlimted SPK-ROCK-DUO Audio Unlimited 900 MHz Wireless Rock Speaker Bundle (SPK-ROCK and SPK-ROCK2) 2 channel selection for you to achieve the best possible performance Phase Loop Lock circuitry automatically locks in and keeps audio signal clear and strong 900 MHz transmitter sends audio signals without speaker wire Weatherproof for outdoor listening Speaker can be up to 150' away from audio source