ECHOES OF BATS AND MEN 



as it travels through the air. This means that echoes will 

 begin to reach the listener after being reflected from a 

 wall 5 feet away just as the last of the cMck leaves the 

 device. If we had a cUcker that gave out a 1 -millisecond 

 sound, this overlap between echo and original sound 

 would cease at distances greater than 6 inches. 



It is interesting to take such a clicker and listen 

 for its echoes. Even the ordinary toys producing 10- 

 millisecond chcks will add significantly to the knowl- 

 edge we obtained with echoes from spoken words. In 

 these experiments it wiU be important to maximize the 

 audibihty of the echoes while reducing the level of the 

 outgoing sound which reaches our ears directly. Part of 

 the echo-suppressing effect mentioned earlier is a very 

 brief reduction in the sensitivity of our hearing for a 

 fraction of a second after the arrival of a very large 

 sound, and these clickers at close range are really very 

 loud indeed. A good procedure is to hold a typical toy 

 clicker with your two hands cupped around it and 

 opened to form a forward facing horn so that the hands 

 are between clicker and your ears. The outgoing chck 

 will still be plainly audible, but its main sound energy 

 output will be directed straight ahead. All the striking ef- 

 fects I have described can be heard on reversed playback 

 of such cUcks. In making a tape recording for reversed 

 playback, you should keep the microphone behind the 

 cupped hands, too, so that it also will be better situated 

 to receive the echoes than to receive the original emitted 

 click. With this very short click we can also begin to hear 

 echoes directly without any tape recorder or reversed 

 playback. 



One of these toy clickers held in the cupped hands 

 can be used to good advantage out of doors. If the 

 hands and clicker are pointed at a building 50 feet or 

 so away, a clear and separate echo can easily be heard. 



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