On larger boats there is often the need to set up a marine stereo system with separate audio zones. For example, someone in the cabin may want the music volume low while those on deck want it loud. The larger the boat, the more of these zones you may want to establish. A house boat may need three or 4 zones while a smaller cabin cruiser may only need two.
A simple 2 zone setup can be accomplished with almost any marine stereo. Most units have four speaker outputs, two for the front and two for the rear. A control called the fader adjusts the volume between the front and rear pair of speakers. Mount one pair of speakers on deck and the other pair in the cabin and there you have it. You can adjust the volume in each zone with the fader control.
But of course, you can get much more sophisticated than this. Some stereos, like this one, are specifically designed with multiple zones in mind. For example, you can mount a wired remote control that will allow audio adjustments just for that zone. Some stereos will accommodate multiple remotes so you can mount one in each of several zones.
You may want more than 2 speakers in a zone and some stereos will allow you to power up to 8 speakers so that you can have 4 speakers each in two zones. Additional zones and speakers can be powered with external amplifiers.
Another method for setting up zones is to use a fixed volume preamp output from the stereo. Not all stereos have this so you will need to look for it. A fixed volume output provides an audio signal that will not be affected by adjustments to volume on the main unit. You can patch the signal from this output to one or more zone amplifiers like this one that each have their own independent volume control. When you set these up in different areas of your boat you can control the volume by adjusting the amp volume control. Keep in mind that not all amps have a volume control, so you will need to look for that specific feature.