sub-woofer
My speaker cones went out in my arch cockpit speakers, so I decided to do an upgrade on those to a better brand, same size, the name of which I can't recall right now. Then I upgraded the interior cabin speakers to "Boston" brand, but same size. Then, at my wife's insistence, I installed a huge box sub-woofer in the main cabin starboard settee, up against the forward bulkhead (Passage 42). The sound comes out directly where the A/C opening is located amidships under the settee seat. Then we upgraded the stereo to a 100 watt per channel. When we did the sound test people were coming over from two finger piers away. I'm not one for loud music, but it makes the softer stuff sound better as well. When we're conserving power we can turn off the sub-woofer by using the speaker selector switch. I have found that even when you're on the aft deck that the vibrations from the subwoofer come through the deck enough to do the trick. If the hatchway and scuttles are opened, it DEFINITELY does the trick. Easy to wire and easy to install, but you have to resign yourself to the weight and space sacrifice. My wife says it's worth it.