A router and circle jig is the best way. However, I now a good router will cost at least $100 and then $20+ for a circle jig. See my attached link to see my router, Jasper jig and homemade jig. I have attached a link to a subwoofer that I built. Just go to page 3 and you'll see the jigs. http://europa70.tripod.com/diy_sonosub001.htm