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.
It’s important to understand that speakers are very directional. That means they push the sound in the direction they are pointed. For optimal sound quality, it is very important to have the speakers pointing directly at the people listening. In fact, the sweet spot is going to be a position with an unobstructed view of all of the speakers in a system.
Not all sound frequencies behave the same. Higher frequencies are very susceptible to being blocked by obstructions. By contrast, lower frequencies are very persistent. That is why you will usually see tweeters mounted up high, while woofers and subwoofers are usually positioned lower. When providing sound for a large group of people, the ideal position for tweeters is actually above head level. That way, the bodies are never blocking the line of sight between the tweeter and all of the ears of the listeners.
Stereo separation is also a very important consideration. We have two ears and our brain determines the location of sounds based on interpolating what we hear from each ear. Stereo replicates that by using 2 speakers to reproduce sound. Ideally you want as much separation between right and left speakers as possible.
Many full-range speakers are actually two speakers in one. You have the tweeter and the woofer. The tweeter reproduces high frequencies and the woofer reproduces low frequencies. This setup is advantageous because each speaker is optimized for the frequencies that it is designed to produce. A tweeter is very good at reproducing high frequencies, but not so good at reproducing midrange or bass. Likewise a woofer will do well with the bass frequencies, but not so much with the high end.
Usually a full range speaker will have a passive crossover built into it. A crossover divides up the frequencies in the audio signal so that each speaker is assigned the range of frequencies for which it is responsible to reproduce. A passive crossover does this with a signal that has already been amplified.
By contrast, an active crossover splits up the frequencies at a preamp level then feeds the signal to two or more channels of an amplifier. That is what it means to bi amp a speaker. You are using 2 amplifier channels to separately power a tweeter and a woofer. You can also tri amp or even quad amp. Usually the more you divide up the frequencies, the higher the fidelity.