The 10 Best Marine Amplifiers

For a boat with four speakers and a subwoofer, the Kicker KXMA900.5 runs the whole system from one case. Kicker builds it to boating-industry wiring and safety guidelines, with corrosion-resistant metal and plastic parts that hold up in damp, salty air. A small bass knob comes in the box, so you can turn the sub up or down from the helm. The catch is that Kicker doesn't publish a clear power split per channel, which makes speaker matching harder.

Built for boats, side-by-sides and motorcycles alike, the Kenwood KAC-M8005 runs five channels from a coated circuit board that Kenwood says resists salt water. Filters on the front and rear channels keep deep bass out of small speakers, so they can play louder without straining. Its efficient design stays fairly compact and cool. Kenwood lists only a peak power figure, not steady watts per channel, so expect less than the big number on the box.

Many boat stereos have no spare outputs, and the JBL MA5055 handles that by taking the speaker wires straight in. Its low white case looks at home on a bright console or tucked under a gunwale. Adjustable filters and a bass boost let you shape the sound for each speaker pair, and a light warns you when its protection circuit kicks in. JBL says little about weather sealing, and the warranty is short at one year.

Tower speakers and subwoofers are the job for the Wet Sounds HTX-2. It drives a pair of channels, or one big bridged channel for a single sub, from a fully sealed case that Wet Sounds designed for boats. The maker rates it at about 150 watts a channel into standard speakers and covers it for two years. With just two channels, it can't run a full boat of speakers alone, so most owners pair it with a second amp.

If your boat has four speakers and no sub, the Kicker KMA600.4 gives each one its own channel. Kicker coats the circuit board against moisture and uses marine-grade stainless screws that won't rust, and the case is small enough to tuck under a console. Built-in crossovers let you trim bass from small speakers. Kicker calls it weather-resistant, not waterproof, so it needs a dry, shaded spot, and the warranty runs one year.

Rockville DBM50 is a budget way to power four speakers and a sub, and it comes with a microphone for announcements plus a wired knob for the bass. Rockville claims a coated board, stainless hardware and full splash protection, though no outside test backs that up. The giant wattage in its name is a peak figure, and steady output is far lower. The speaker channels use an older design that runs warm, so give it open air.

For little money, the Skar RP-150.4ABM puts about 150 watts of clean, steady power into each standard speaker channel. Skar coats the board against water, paints the case to resist rust and adds a two-year warranty. It uses an older amplifier design, so it's long, heavy and runs hot. Plan a mounting spot with room and airflow, and ignore the bigger wattage printed on the case.

Boats with no stereo at all are the reason to look at the Boss MC900B. It pairs with a phone over Bluetooth and drives four speakers on its own, while a small wired remote handles volume, track skips and phone charging. It's a simple, cheap way to add music to a pontoon or a golf cart. Boss calls it weatherproof rather than waterproof, so mount it under cover, and its power is modest for big outdoor speakers.

Jet skis, UTVs and motorcycles leave little room for an amp, which is where the NVX VADM4 v2 fits. It's about the size of a phone, with a coated board for damp rides and enough power to make small speakers play cleanly over engine noise. A lit logo adds a bit of style if it's mounted in view. The output is modest, though, so it won't do justice to large tower speakers or a subwoofer.

The Infinity M704A is a modest step up from the small amp built into most marine stereos. It accepts either the stereo's low-level outputs or plain speaker wires, and its adjustable filters protect small speakers from deep bass. At about 70 watts a channel, it suits standard boat speakers rather than towers. Coverage lasts only a year, and there's little owner feedback yet to judge how it holds up over several seasons.