This appeared: https://www.facebook.com/groups/6110761372/permalink/10154485012031373
Instructions: http://tapeop.com/tutorials/119/build-your-own-spring-reverb/

And I also happen to have one, so this is what it sounds like:
Acoustic guitar being played through a spring.. (iPhone recording, also picking up acoustic part).

Guitar output is muted, not mixed, you are hearing pure spring effect. Guitar is amplified via soundcard left channel, and fed via headphone OUT into 3W PAM840 audio amplifier which drives the 4Ω input coil, OUTPUT coil is about 120Ω and being connected to HI-Z right channel. Enjoy

On the second thought, maybe this is not a very good example, I should probably record a sample directly from a sound card.. for it to be pure... make it interactive?

Freq scale at the top, might also do a sweep, the highs are not very vivid :D