Here at Zerotronics, we're always on the lookout for interesting and unusual reverb technologies. So when we saw some crazy looking springs for sale on eBay, we bought them, sound unheard. They were manufactured by Baldwin, sometime in the late 60's (forty year old NOS!) for use in electronic organs. They looked pretty bizarre and we expected them to sound as they looked, thinking that we might be able to turn them into some kind of wacky fun-verb.
But when they arrived and we started listening to them, we were amazed to hear a very smooth reverb tail with a remarkable degree of diffusion. Some research into the patent database revealed the secret: a unique tapered spring design that creates a delay line in which the delay time is inversely proportional to frequency. Quite simply, the high frequencies propagate through the spring faster than the lows.
After a few email exchanges with the seller, we managed to hook up with an organ tech who had a small stash of these mechanisms in his warehouse and of course, we bought all of them. Not that many, but enough to produce a limited edition of ten units (plus a few extra to keep for ourselves).