Sound Telescopes

Mylar spheroids can be used to make giant (8 ft. dia.) dishes suitable for collimating sound, enabling a conversation to be carried out in whispers across the room. The concentration (focusing) of sound can be demonstrated on a smaller scale. Connect a small funnel to a 2ft. length of rubber tubing. Find a large shallow mixing bowl or a wok to use as the reflector. Aim the large mixing bowl toward a wind-up alarm clock across the room. aim the funnel toward the mixing bowl (this collects the reflected sound from the bowl). Listen to the sound through the rubber tube. You may be able to hear the ticking of the clock from as much as 20 feet away. If no clock is available, try using a radio with volume turned down low.