As it’s springtime, here’s a spring reverb made using spectral delays:
SpringReverb.csd (12.2 KB)
Spring Reverb
Sounds very cool Iain! The boing window is very interesting, I see (hear) a lot of sound design potential there.
Just having a play around with this now. The ‘boing’ feature can produce an outrageously fun sci-fi sound 
The ‘boing’ is actually based on observations of impulse responses of spring reverbs where you can see how an initial time-aligned impulse is spectrally smeared, and increasingly so as the reflections bounce up and down the spring. I assume this time smearing is related to transverse waves in the spring.
Wow, it looks pretty crazy when you see it in the frequency domain. Looks more like the result of some digital process than an analogue one.