[RWebb]

Sure thing (can you send me your Cayman?)

I think I misunderstood your question -- you don't want the bats to hear something you broadcast, you just want a recording to play that humans can hear, and want to incorporate that into a display at his poster session... (?)

the latter should be easy you just need the cheapest device that will play back a digital sound file (or an analog one) -- a laptop with a security cable could be used - or maybe a smart phone with a speaker; give the user a button the display to push with mouse or finger

or you could use a tape recorder and have it cycle (if the adjacent poster people don't object)