Cloth backing on drivers

Hi all,
I scored a set of Royd Prior speakers and had to get new drivers for them. During my research, I heard that these speakers had cloth wrapped around the LF drivers. Was this common? The source I heard this from was experimenting with different types of fabric to see what works best. Apparently it subdues the bass a bit and tightens things up.
I've installed new Vifa LF drivers and they sound great but am curious about this extra step. Any info is appreciated.

Path:
Uturn orbit, acrylic platter, cork mat
Art DJ pre
Yaquin MC10L
Royd Prior's