Marquis spas "Soundsations" is a nice system. Instead of pop up speakers or molded shells that have to have a special cover they simply use the cone shape of the spa as a speaker itself! There are three very important parts to a speaker that help you get the sound; First is the Transducer that actually creates the sound vibrations.
Second is the cone, here is a quote from the Tweeter.com
The cone is the large part of the speaker that actually creates the sound by moving back and forth. A speaker cone needs to be stiff and light in order to work well. It also needs to be water resistant. The surround is the piece that connects the cone to the speaker frame. The surround needs to be flexible, yet durable. Different manufacturers use different materials for their cones and surrounds. If you are careful to avoid uncoated paper cones and foam surrounds you will be sure to pick out a speaker that will last.
Although the shell of a spa seems fairly stiff, if you consider it in size proportion to a small speaker you understand that it does have enough flexibility.
Last, the dome of the speaker, controls the vibration and fine tunes the sound. This in the "Soundsations" is the water of the spa.
Think of it this way, if you could set in the middle of speaker without modifiing the sound, you would not only hear the sound but feel it! It is very cool....
There are better sounding units from the outside of the spa but the aspect of being able to
feel the sound is very unique.
