Five channels is a common configuration for boats running four main speakers plus a dedicated subwoofer channel - cockpit and cabin speaker pairs driven independently, with the fifth channel specifically sized and tuned to power a marine subwoofer for real low-end output that satellite speakers alone can't deliver. Like the rest of the MVi line, it's built in a cast alloy chassis with a marine-grade powder coat finish and corrosion-resistant hardware and connectors, rated to withstand salt air, spray and boat vibration well beyond what a car-audio amplifier is designed for. This is aimed at boat owners upgrading to a genuinely capable marine sound system with dedicated subwoofer output, rather than just adding a few extra deck speakers to a factory system. Like the rest of JL Audio's MVi range, it supports Bluetooth-based tuning and monitoring through JL Audio's companion smartphone app for adjustments made right from the boat.