infinite echo?

Question

Is there any way in which a sound could echo infinitely given the right surroundings, for example in a cave system?

Answer 1

I think no. Eventually, the "sound energy" would dissipate away. Here's why:
A soundwave is a compression wave travelling through the air. In the first instance, the wavefront diverges from the source, such that the sound intensity decreases the further you are from the origin. (If you had a point source, this would follow inverse-square). Secondly, when the wave front strikes a reflector, (like the cave wall), the incident energy is split up. Some is reflected (as the echo), some will be transmitted through in to the stone (or whatever other medium it hits) in proportion to the relative compressibilities of the two media (in this case air and rock), and thirdly some will be dissipated as heat at the interface. As any given point you choose, the energy intensity will decay at a steeply exponential rate with time therefore. (I say exponential because the amount of energy lost to any cause will depend on how much arrives there). Even if you could set up a closed system, with no energy losses to the universe in general, you still wouldn't be able to set up an infinite echo. As soon as you 'listen' to it, or somehow detect the sound, your ear or microphone absorbs some of the sound energy and the whole system collapses.

Interesting question though, thanks.

Answer 2

No. Acoustic energy is absorbed by the air (and turned into heat) as the wave propagates through it (which is the reason you can't hear someone talking in a normal voice when they're 100 m away)

Doug

Answer 3

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Answer 4

no. the sound would eventually dissapate.

it is however possible for sound to resonate for a long time. i once visited this dome of a cathedral, where if you put youre ear to the wall, you could hear conversations that happened hours ago.

Answer 5

nope..same as lookin for perpetual motion

Answer 6

interesting thought to which i can not answer

regards x kitti x