Boss Audio 5.25 Round 2-Way Marine Speakers Boss Audio MR50B 5.25 Round Marine Speakers. Boss Marine Loudspeakers are designed to withstand the harsh conditions of the marine environment. All frame and grill sections are made of a polymer composite that is completely waterproof with a coating to protect against damage from UV rays. We use rubber surrounds and polypropylene cones to complete the waterproof package. The tinsel leads are coated to prevent corrosion. In addition to the material engi