Marine audio system architecture (Fusion, JL Audio, marine speakers)

Modern marine audio breaks into three parts: source (head unit or streaming device), amplifier (usually external Class-D for real power), and speakers. HEAD UNITS: Fusion Apollo RA770 and Marine Audio System are the market defaults, NMEA 2000-connected so volume can be controlled from a Garmin/Simrad/Raymarine MFD, Bluetooth + AirPlay 2 for streaming, multi-zone output (typically 4-6 zones for a yacht: helm, cockpit, salon, master cabin, guest cabin, engine room shore-side). AMPLIFIERS: JL Audio MX or M-Series marine amps, Class-D, marine-coated boards. Rule: match amp output to speaker RMS handling, not peak, a 100W amp into 200W-peak/50W-RMS speakers will destroy them at half volume. Sizing: for full-size marine coaxials at cockpit, 75-100W RMS per pair; for subwoofers, 300-500W RMS. SPEAKERS: marine speakers use polypropylene cones (won't rot), stainless or plastic grilles (won't corrode), UV-stable materials. Rated IPX6 or IPX7 for wet install. Marine speakers cost 2-3x automotive equivalent, but automotive speakers on a boat die in 2 seasons. Common install mistakes: (1) Running speaker wire in the same conduit as engine harness, pickup noise, ground loops. Route separately. (2) Underpowering the amp, an underpowered amp clipping does more speaker damage than an overpowered amp on clean signal. (3) No fusing at the battery, every amp needs a fuse within 7 inches of the battery positive per ABYC E-11. Subwoofer install: sealed enclosure only in a marine environment (ported enclosures amplify road/wave noise and can suck water spray backward through the port).