Richard - I find the word multi-spring can be misleading.
We are actually joining (glueing) single leaf springs to make one thicker one.
Think of a truck with a leaf spring in the back.
leaf spring suspension I see this as similar physics except we are working in a horizontal fashion not a vertical one.
The suspension becomes more compliant if we remove leaf springs from that truck. More firm if we add springs. As we add springs we need to add weight to the truck otherwise it becomes bouncy on the road. The ET2 is the same. As we add a leaf spring or two we need to increase VTF if using the same cartridge. We also need to keep the inert lead weights at the end of the I Beam for resonance control – away from the air bearing.
MOST ET2 users go wrong with the lead weights - imo - because they are coming from developed habits with a pivot arm. What do you do to increase VTF with a pivot arm? You bring the weight in more toward the bearing. The ET2 is a unique tonearm unlike any other with a decoupled counterweight. The weight needs to stay at the end away from the air bearing to not impede it and for resonance control – away from the air bearing. So we just add a weight and keep it at the end.
My direct experience – adding a leaf spring (glueing two together) to the ET2 or Et2.5 means it can carry a higher load (heavier less compliance cartridge) better. The result in sound with heavy MC is amazing. Bass is further tuned to your room by turning the counterweight cap downward or upward. This will depend on your actual room and how good your bass compression is with the speakers you are using.
Thanks again to Frogman for bringing the double and triple leaf spring to the discussion here. Bruce has been shipping loose leaf springs out with his tonearms for years. His customers probably look at them and think - wth is this for - maybe a spare ?