A stealth shape that actually works

Square shaped objects are ot perfect in their shape; when you are exactly at a 90 degree angle the shape will reflect radar.

So if you make a concave surface, it will absorb the sound. It is not easy to make an outer hull concave, but not impossible.

 This shape works for sonar also.

 This also brings up the point on why saucers seem to spin quickly. When you use sound to create room temperature super conducting material, it is very sensitive to the sound in its environment; the sound knocks it out of alignment. But it you put that material in the middle of a spinning top, this shields it from the ambient noises of its environment.
It saucers are using Earth's EMF field for propulsion and levitation, they would appear at times to have jerky movements, for the Earth's EMF varies all the time.