Here's a
link to the RumbleRoad speakers I use on my Harley. The ones I got have the amplifier built on to the back of each speaker. I use them with an iPod and it's plenty loud enough even with the loud Harley pipes and at 70 mph speeds.
Above that the sound quality starts to suffer, obviously rock music comes through better than soft jazz.
I test rode a GL1800 (no rear speakers) and plugged my iPod into the auxillary and it sucked compared to the RumbleRoad speakers on my RoadKing.
I've removed the speakers from the chrome housing they came in and installed them in a custom fiberglass enclosure built for the RoadKings windshield and they sound even better that way.
I can't imagine how great they will sound when I put them on a nice quiet ST1300!
Here's a few pics of the actual speakers while I was installing them on the Harley
pic1 and
pic2
Here's a pic of the
RoadKing where you can kind of see the box I'm talking about, I hope to make a similar one for my new ST1300...as soon as I can sell the RoadKing and buy one that is
Hope this helps.