Whether you use rubber feet (isolators) depends on what the floor is made of.
For suspended wood floors not having isolators will allow the vibrations through the floor so you will get to feel it with your feet, as the floor will move as well as the sofa.
For concrete floors they are a must as without them the transducer is trying to move against an unmovable object, (Planet Earth). The isolators act like shock absorbers. They compress with weight but still allow the transducer to move the sofa both up and down.
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