MRDF-4

It's rated 700W Dyno-Certified RMS: 175W x 4 at 2 ohms, 115W x 4 at 4 ohms, or 350W x 2 bridged at 4 ohms. That's enough to run tower speakers and cabin speakers at full volume and still sound clear over engine and wind noise at cruising speed.

Mostly power. The MRDF-4 puts out 700W RMS compared to 400W on the MRDF-3, and it's slightly longer at 10.43" vs. 8.86" to fit the extra power. Both have the same marine-grade build, silicone terminal covers, 50Hz to 250Hz crossovers, and 4 AWG power terminals.

Yes. Bridge two channels for 350W into a 4 ohm subwoofer, or bridge both pairs to run two subs. Set those channels to low pass (50Hz to 250Hz) so the subs only play bass.

Yes. The circuit board is conformal coated against moisture, salt air, and humidity, the hardware is all stainless steel, and the chassis is UV and salt resistant. The included white silicone terminal covers seal the power, ground, remote, and RCA connections against spray and salt corrosion.

It's built to be easy on the battery. The Class D design runs at 85% efficiency at 4 ohms (76% at 2 ohms) and draws only 1 amp at idle, so more of the battery's power goes to the music instead of heat. It runs on anywhere from 9 to 16.1 volts.

The MRDF-4 has 4 AWG power and ground terminals and 10 AWG speaker terminals. It's protected by four 20A internal fuses (80A total), and spare fuses come in the box. A wiring kit isn't included, so plan on a 4 AWG marine amp kit.

Input sensitivity adjusts from 224mV to 6V, so it matches both low-output and high-output head units through the RCA inputs. Tiffany-style RCA jacks keep the connections tight on rough water and help prevent corrosion.

Set each pair of channels to Full Range, Low Pass, or High Pass, then set the filter anywhere from 50Hz to 250Hz. High pass keeps deep bass out of small marine speakers so they can play louder and cleaner. The clip LED shows when you've hit distortion, and thermal, short-circuit, and over-voltage protection keep the amp safe.