Hello.
If anyone wants to investigate acoustic mirrors then have a look at :
http://www.andrewgrantham.co.uk/soundmirrors/
Nice!!
I was once shown, some years ago, an "acoustic laser" (maybe at the
University of Maryland Baltimore County campus??): Two large
(half-meter diameter) curved metal mirrors (like shallow woks, or the
curved metal dishes kids slide down snowbanks on), spaced maybe two
meters apart on an optical table to form an acoustic resonator. In the
middle a chunk of "acoustic laser material" consisting of a little
match-box sized box with an omnidirectional microphone at each end, with
each of these connected through a tiny transistor audio amp to a small
speaker on the opposite end.
Took up a lot of table space -- but "lased" nicely.