The visitor can *see* the vibrations, caused by their voices. A laser beam hits a small mirror, mounted on a rubber membrane, which vibrates when you sing into the tube. The reflected beam creates an image on a white screen 10 - 15 meters away. Different people creates different (Lissajou-)patterns, depending on their different voices and pitch.
The stand can be prepared for fixation to a railing or directly on the floor. Please specify which you prefer. The scene normally is a white wall, i. e. it is not part of the exhibit.