The Sith masturbation sphere was an ancient piece of technology devised by Naga Sadow, ruler of the Sith Empire. Calling upon Sith magic and the tumescent Force energy of its occupant, the sphere could amplify and focus the energy and malice into powerful magic effects, such as illusions, telekinesis, or destructive force.
Naga Sadow frequently went into his masturbation sphere for hours or even days at a time. Sometimes his Sith adepts would knock on the door, saying, "Naga Sadow, what are you doing in there?" and Sadow would assure them he would be right out in just a minute and never mind those thumping noises. Using the masturbation sphere was a delicate process. One had to spend a great deal of time allowing the Dark Side energy to build, grow, rise, swell, expand, and only releasing the energy when the peak had been reached, or else the Sith Lord risked blowing his wad prematurely.
Thousands of years later, Abeloth managed to commandeer one of the spheres. She added vibration features to the design.