1/2 PEI diaphragm tweeter. 5.0 bluetooth wireless music streaming, Built-in 2 channel amplifier. Bluetooth feature Voice Coil Impedance:4? +10%. Voice Coil Size:25mm. Voice Coil Material: ASV. GUZARE marine series of head units and remotes are fully tested against UV radiation degradation as well as tested to IP66 water intrusion standards.