The transmitter for this speaker set is designed to work with a wide variety of devices. The tests have shown the default volume levels of iPods, MP3 players and other devices connected to the transmitter through the headphone jack does not have the signal strength required by the transmitter. Raising the volume of your device will increase the signal strength to the transmitter. The blue signal LED will light when the required signal strength from your device is reached. It's recommended that you keep the volume set on your iPod or MP3 player at a minimum of 3/4 of full volume.