Less than 13 inches
dont know for sure
I know my klipsch woofer is 13 and the logitech woofer is smaller z-680's $209 at amazon.com
System Spec's:
Asus P4c800-E 3.2e @3.8ghz
1gb corsair xms pro2-2-2-5 aiw 9800 pro
audigy 2zs klipsch ultra's
74gb raptor wd 2000jb
pioneer 108 pioneer 120s