The electronic peasant has an interesting project, prime for audio investigators –
There are a number of different ways to send vibrations travelling down a spring, but most spring reverbs use torsional (rotational) motion, which is less sensitive to interference from external vibrations. Here is an experiment that The Peasant did with a Slinky Jr (R) and some old speaker drivers which delivers loooonng delay low frequency DIY reverb for almost no cost.
Not the simplest fun you could have with a slinky, but definitely looks worth a try. – Slinky Spring Reverb
Or, if your after a more professional, albeit more costly, sound –
check out the Center Stage reverb project