When you take a close look what happen in the excursive movement of twin-roll rubber surround for a speaker, You will find the twin-roll is a much better surround in speaker application. The reasons are as follow:

The forward and backward excursion of twin-roll surround is more "even" than the traditional single surround did. We can see the forward excursion uses inner roll, and backward excursion uses outside roll. So the twin-roll rubber surround is closer to the ideal excursion. From our experiment, result also proved this. It is very good for woofer design.

The linearity is a very important factor for a speaker driver design. We need the driver has better alignment during excursion. Most of driver designer know the narrow surround has better alignment, but its excursion is limited. The twin-roll owns the benefit of narrow surround and longer excursion.