Regarding stiffness, there are two separate issues. One is the suspension, and a stiff suspension raises resonance and mechanically damps the motion. This has an influence on electro-mechanical parameters. The other issue is cone stiffness. This sets cone flex behavior. A stiff cone may remain pistonic up to a higher frequency, but when it begins to flex, the ripples across its surface may be heavily resonant. This kind of breakup causes severe response anomalies. The cone can be made with material that is less stiff, but more well damped internally. This kind of cone will become non-pistonic at a lower frequency but will behave better when it does.