Most speakers, even the high quality ones, have paper cones. Paper is a superior material for sound reproduction. Unfortunately, it doesn’t do well when exposed to water. That is where waterproof marine speakers come in. Waterproof speakers have cones constructed of polypropylene and other plastics that won’t be damaged with splashed or rained on.
All of the same rules for positioning your speakers apply to the outdoors. If you are mounting marine speakers on your patio, for instance, you still want to get your tweeters up and your subwoofers down wherever possible. Mounting waterproof speakers in a gazebo or under the eaves of your roof is a good idea.
Speaker wire outdoors needs to be treated a little differently. Copper is highly susceptible to corrosion so you want to make sure that the wire cover is intact from end to end. It isn’t a good idea to have wires spliced because that is an avenue for water to intrude. It is always a good idea to use a dab of silicone or liquid electrical tape on the speaker connections to reduce the risk of corrosion.