The tweeters aren't going anywhere, the velcro is rated to something silly like 10kg vertically, and it's holding about 50g horizontally.

The sub is a slight concern in the event of an accident, but it really doesn't have any room to move at all - both seats are wedging it into place. So it doesn't have any room to build up momentum in a head-on collision.

Nothing moves at all in 'spirited' driving.