There is no substitute for cubic inch or in this case surface area

Discounting surround widths, cone depths, voice coil dust cover diameters, and any additional surface available from any ribbing in the cone itself:

6" dia. = 28.27 sq. in.

8"  "     = 50.27  "   "

10"  "    = 78.5   "   "

12"  "    = 113.1  "  "

18"  "    = 254.5  "  "

pi x radius squared for anything else....

I play with truncated cone surface areas.....

Mine work out to be about equal to about a 9" dia. in the diameter of a 6"... ;)

Voice coil suspension and travel is whatever I want to play with, keeping in mind the surround pistonic travel will require.  And not a lot of concern over tariff ruckus for the immediate future....

Mix 'n match to your pleasure, J

"Just doin' a little Hartley hammerin'....." *L*
Keeps the skin supple....try that excuse on the sig other... ;)) 

Let me know if it works at all....😎