PA D Series 5-Channel Class D Amplifier, PA D5000.5, Polk Audio, runs much cooler than conventional amps., power supply with outputs stable into 2 ohm loads for full range channel speakers and 1 ohm loads for subwoofer channel., thermal, DC offset, reverse DC voltage and short circuit protection., line level inputs for subwoofer signal from head unit, in the INT position, the amplifier will filter the bass frequencies from the full range signal and send them to the subwoofer amplifier channel., attenuates the frequencies below the settings on the control., set gain to match output from head unit., selects between no filtering or a high pass filter to dial in your speakers' blending., in the ST position, the amplifier sends the same signal to the front and rear channels., ensure maximum signal transfer., Used throughout and will not corrode in humid environments.