partsexpress.com sells speaker surround (the little foam part is called a surround btw) repair kits fairly inexpensivly. JL (if their not under warranty) proably chargers 30+shipping per speaker to do a little repair like that. They're definately not trash event it their surrounds completely fall off. The surround just controls upper liniar excursion, it will cause a loss of back pressure to the sub if its not repaired but it will not cause the sub to fail.
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I'm a Mechanical Audiophile