Audio Systems: Blown Subs, thud, subwoofers

Question
I have two JBL 12" subwoofers and I think that one of them is blown. Is there any way that I can tell that they are blown physically, like by looking at them? I have both of them out of the box that they were in, and they look like they are in perfect condition, but I can't tell which one is busted when I turn them on.

Answer
Tim ,

 sound is about the only way unless you have had a major blow which normally dont happens ... turn them on inside or out of the box and listen close the one that has a dead THUD sound or clicking ect.. thats the one with the blown coil also smell for any burnt electric smell on the sub this can also be an indicator but sound is the best tool to trackin down the problem .. hope this helps you out if you need anything else let me know

thanks