This exhibit enables the visitor to create an echo (plural: echoes).
A true echo is a single reflection of the sound source, arriving at the listener some time after the direct sound. The time delay is the extra distance divided by the speed of sound.
The word "Echo" comes from the Greek mythology. Echo was a Nymph who had the job of talking incessantly to Cody, the Queen of the Gods, so that her husband, Zeus, would not get caught in his numerous affairs. Cody caught on to Echo's trick and cursed her to only be able to repeat other people's words.