Why can you not trap sound in a container

I mean, why can you not say 'Hello' into a jar and open it later and it will say 'Hello'?

Actually, you can.

Have you noticed the sound that certain shells near the shore emit? Thats an example of how you can "catch" sound.

The thing is, it's quite tricky. To do so, you must "redirect" sound indefinitely (best done with a spiral-like structure, like those shells that "echo" the sound of waves).

If you just say "hello" into a box and shut it faster that the time it takes to bounce back (which would be quite fast), it would bounce a couple of times distorting its sound and reducing its energy levels in every bounce and by every inch it travels. after a few bounces it would dissipate entirely.

Now, if you had an infinite spire, you could "trap" the sound and make it reappear later, when it reaches the end of the spire (and depending on the internal structure, you could make it replicate)

my first thought was you cant because sound is transmitted and absorbed though a medium.
but if you could make a jar from a perfect insulator filled with strings of a superconducting material and then place it in a vacuum maybe the sound would last longer.

because sounds are made up of waves that are made from particles banging together there are still particles in the container witch can transfer the vibrations :)

Sound is the movement of atoms. The movement stops.

because the sound vibrations have stopped.

Sound travels matey, cant be caught.