Sound (Whisper) Dishes

Principles of Science: Sound Reflection, Speed of Sound

“Speak softly and carry a big voice.” This is exactly what happens when a visitor to the Whisper Dishes whispers into the focal point of one of its twin dishes. A listener with an ear to the other dish, positioned about 30 feet away, will hear the voice as if its speaker were standing beside him!

The sound dishes make use of their parabolic shape. The phenomenon of the paraboloid is responsible for the transfer of a normal voice over an uncommon distance. It does so by collecting the sound waves and reflecting them towards the opposite sound dish. That opposite dish, also a paraboloid, takes those sound waves and directs them to its focal point and the ear of the listener. The delay between when a person talks and when the user at the other dish hears them demonstrates that sound travels at a certain speed, and it takes time for it to cover the 30 foot distance.

Paraboloids are used to collect many types of waves, and are used in applications ranging from flashlights and automobile headlights to radio telescopes.