Radio or stereo components may be needed underwater and the stereo industry has answered with specific products for use. But they need not be immersed at all to produce sounds beneath the waves. They could use amplification that could be installed specifically on surfaces that are immersed into the sea with ease.
Products like these are specially made and more expensive because of it. Marine speakers have relevant uses for both entertainment and safety. There are other concerns that apply and the need is to have these safely set up and with strong enough settings so that they could withstand wave action and water pressure.
Like submarine hulls these also have specific strength when it comes to water pressure and most if not all are unable to work too deep into the water. In any case, most speakers are installed on surface vessel bottoms. But there are units specially made to withstand deeper waters, but these could be military grade stuff for submarines.
Civilian use could be commercial in nature, for instance, and this could mean water and amusement parks which operate some underwater features. They could have shows were people are tasked to dive into pools and swim with the trained animals. They might also provide sounds to the animals themselves who might respond to calls.
Some of these are put to good use in rescue units, like Coast Guard cutters and other stuff that might apply. Underwater sound is muffled so these need to be more powerful than usual, so that even semi conscious persons could hear them. These are relatively costly and the demand is exclusive to some circles like the military.
Civilian use is relatively light when compared to the military or paramilitary one. But then civilian set ups are not tasked to go through the harshest marine environments. Submarines for instance could dive deeper and the pressure really gets strong when they do, but the speakers are needed there for any emergency purpose.
The stuff is composed of the most durable of components that could withstand immersion. The insides are protected and sealed in just like the diving bell is. There are some coated cables and electronic parts which could be exposed to the water, but most are located on the inside and in any case sound could get through specially set grilles.
The Coast Guard will use theirs to rescue civilians who may be trapped underwater. Divers could also use portable sets to get close and relay instructions to those trapped persons who need rescuing. This means that the speaker system itself is of high decibel levels to really work underwater, to reiterate, and may operate on powerful batteries too.
These are hailers or megaphone style items since no one could really appreciate music in the water. However, there is also use for these in research vessels which might be trying to contact whales or dolphins. Or talk to them through the use of their own sonar calls that are said to contain a complex set of linguistic items.