Echoes of a stretched egg

Sound waves bounce off people as if each person were an enormous, stretched-out chicken egg, scientists reported recently at a meeting of the Acoustical Society of America. The discovery could help designers build better concert halls or other buildings where sound is important.

For the purposes of reflecting sound, people behave as if they were shaped like elongated eggs.

The shape of an object determines which way sound bounces off of it. Two years ago, a pair of researchers from France discovered that they could use sound to determine the shape of an object as it moves around in a tank of water. This finding suggested the possibility of using sound as a way to identify and count different species of fish in the ocean automatically.

Fish can be hard to handle, however, so the researchers chose to work first with people. In one experiment, people walked around inside a hard-walled room, while the scientists used microphones to record echoes of sounds produced by speakers. Participants ranged in age from 3 to 55 years.

Analyses of the results showed that each person reflected sound in the same way as would an egg of his or her size. From the viewpoint of sound waves, most of us would have shapes that are somewhat taller and thinner than an average egg.

Now, would you like your sounds scrambled, boiled, or fried?

Going Deeper:

Weiss, Peter. 2003. Humpty-dumpty effect: Acoustically, people resemble large eggs. Science News 164(Nov. 15):308. Available at http://www.sciencenews.org/20031115/fob3.asp .

To learn more about the science of sound, see www.sci.mus.mn.us/sound/nocss/top.html (Science Museum of Minnesota) and library.thinkquest.org/19537/Main.html (ThinkQuest ’98).