how does one know whether bottoming out a woofer o

Usually if you damage the woofer it will sound heavily distorted. It's very obvious if you listen for it.

When woofers bottom out they often make a violent CRACK! sound as the back of the moving cone hits the stationary frame. Undamaged woofers can achieve this state by being powered beyond their design limits. Actual physical damage soon follows.

thanks! that all helps alot. viridian, i will try that, but i am unsure what the dust cap is exactly. rockvirgo, my sub has 2 eight inch woofers, one DOES make that crack, i have described it as a smacking. the other does not. therefor i ponder whethter one is dmged or not. i feel like it is bottoming out, but not sure. thanks again all.