In simple spring reverbs, the input and output transducers are coupled by one or more single springs. When the sound, as rotational vibrations, travels down the spring, from input to output, it is reflected back to the input, and again, back to the output. This creates a pattern of reflections in the output. If the spring delay time is T, the delayed sound at the output is (T, 3T, 5T, ...) since each addition delay requires two trips along the spring.
The four Accutronics® Type 9 reverb units that are used in the CoolSprings have three pairs of coupled springs each. Since the couplings both transmit and reflect vibrations, a more complex reflection pattern is created, due to the additional reflections that occur between the couplings and the input and output transducers.
What many people do not realize is that the coupling positions are varied randomly as each reverb mechanism is assembled. This gives each Type 9 reverb unit a unique pattern of reflections.
This means, of course, that each output channel of the CoolSprings, which combines two Type 9 reverbs, will have a unique pattern of relections. When you pan them into a stereo mix, even though the two channels will sound similar, the reflection patterns of each will be slightly different, creating a very natural sounding stereo effect.
This also means that every CoolSprings system, which contains four Type 9 reverbs, will have a unique pattern of reflections. The one you own will not sound exactly like the one that anybody else owns. And if you buy more than one, even if they have the same decay times, they will not sound exactly the same...