Hi amnesia

>
>>You can lay something on the springs, which changes the sound
>>[...]
> Oh very John Cage :-)

Thats not John Cage, thats - as far as I rember - Dynacord or Echolette
or some similar german company:
I have seen a spring based reverb box in a studio in Frankfurt in the
late 70ies, which had two mechanical attachable devices. One was a short
piece of cloth which could be attached to the spring start by a lever
and acted as a HF damper. The other was a kind of brush with something
like lametta hanging from it instead of brush pins, which could be
attached to the springs and its position could be moved; it added some
nice sizzling the the reverb.

I don't know whether it was single custom made device or whether it was
a regular product.

Florian