956. How does a sound dish work? I know that it's a parabola, but I can only find drawings not explanations. — DW, Omaha, NE
A sound dish is actually a mirror telescope for sound. When sound waves from a distant source encounter a rigid parabolic surface, they reflect in such a way that they focus to a point. If you put a microphone at that point, it will detect the sound waves from the distant source. You can see this focusing effect by drawing a parabola on a sheet of paper and directing parallel lines—the sound waves from the distant source—toward the parabola. If you reflect each line in a mirror-like fashion from the surface it hits, you'll find that all the reflected lines pass through a single point as they move away from the parabola.