All day echo chamber, is it possible?

[Aghanim]

After I rewatches Avatar The Last Airbender, someone there mentions a all-day echo chamber. Is it physically possible, or the wall would absorb too much energy?

[Tex_NL]

In physics there is no such thing as 100% efficiency.

The walls will always absorb a tiny fraction of the energy. Even the molecules in the air, which are necessary for the sound to travel, absorb a tiny amount.

[Kerbart]

Even if the room would have 100% efficiency, in order to hear it your ears would still be absorbing some of the sound. One can argue that you don't have to be in that room, but if a tree falls in a one day echo room but there's no one around, does it really make a sound?

[Aghanim]

So, what is the upper limit of echoes?

[sgt_flyer]

Current world record for longest echo seems to be 75s - in a oil tank in scotland.

http://www.dailymail.co.uk/news/article-2540379/Oil-tank-Scotland-sets-record-worlds-longest-echo.html

They shot a blank for the test (the sound file is in the article) - that makes an incredible sound (almost like a rocket engine sound fading away : p)

[NFUN]

[insert political forbidden FOX News/MSNBC joke here]

Also, Avatar is fantastic.

[cantab]

If the sound is loud enough, the entire Earth can become it's echo chamber. Eg the Krakatoa eruption.

[vger]

Just cheat, use microphones and speakers to create an infinite feedback loop

[magnemoe]

Just cheat, use microphones and speakers to create an infinite feedback loop

you must have some delay too, if you just connect them directly you only get that nasty feedback sound you probably know.

You can even get it on radio then people call in and use the handfree mode on phones while the radio speaker is close.