So here's the situation I'm in; I had this really weird dream with this really weird instrument in it. It was kinda like half a dulcimer with springs on it. There were 11 springs on it, (But I'm pretty sure it was supposed to be 12, corresponding to the 12 steps of the western scale) That acted kind of like sympathetic strings or a tremolo in a guitar. So my real question here is, How do you tune a spring that's under tension, or rather in what way do you put it under tension? the only way I can think of is putting one end of the spring on a sort of tuning pin and turning in the direction of the spring. Would this work?
Springs will have too many and too slow vibration modes to be useful for an instrument I would think. For example, springs are used in "spring reverb" by putting a signal in in one side and picking off the resulting torsional vibrations as the signal propagates back and forth through the spring.
Just off the top of my head, I can think of three different types of springs. A leaf spring could probably be tuned in the same manner as a xylophone tyne. A coil spring that is at rest when expanded, and a coil spring that is at rest when compressed, would need to consider size, weight, material, applied tension, and more. I imagine the original question was actually intended to "stump the band" and had in mind a device or method already developed that could be used for that purpose. You very well may need to become inventive.