This is the amazing conclusion drawn by scientists who usually study fishes, but thought that experiments with humans were easier to control than with fishes. Science News tells us the whole story, which could lead to improvements and better designs of concert halls and other places where sound is a major concern.
Using a sound-based scanning technique to determine the shapes of moving creatures and other objects, an international team of scientists has found that the human form bounces sound waves as if each person were a huge, elongated chicken egg.
To arrive at this new acoustic representation of people, [the researchers] placed a speaker and a microphone in each of two reverberant rooms -- a squash court and a fallout shelter. Next, the scientists had a person walk around in one of the rooms, while they recorded the many echoes that resulted from audio pulses emitted by the speaker. The team conducted tests with 27 people from ages 3 to 55.
Here is how they conducted their experiment (Credit: Stéphane G. Conti, NOAA, Southwest Fisheries Science Center).
Here are some -- very -- technical explanations given by the scientists about the scattering and absorption measurements they did, extracted from the presentation they gave at the 146th meeting of the Acoustical Society of America in Austin, Texas, "Let's hear how big you are."
The human moves in the reverberant room between the shots k and k+1 (a and b). The reverberated acoustic waves are recorded on the microphone (hk(t) and hk+1(t), c and d), and the coherent intensity corresponding to the acoustic waves reflected on the boundaries of the room (e, Sc(t) blue) can be separated from the incoherent intensity due to the human motion (e, Si(t) green). The ratio S(t) of the coherent and incoherent intensity (e, red) decreases linearly with time. The slope depends on the scattering cross section of the human.
The abstract of their paper, "Measurements of the total scattering and absorption cross-sections of the human body," doesn't carry such a sexy title.
Source: Peter Weiss, Science News, Week of Nov. 15, 2003; Vol. 164, No. 20
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