It to ruduce the vibrations, you wont to hear the music NOT the vibrations from the fiber glass, wood is better has better acoustic's and less vibratiuon problems easier to pad and brace than viber glass which is to light without added struts and braces to minmize it, however they have a tendency to come loose if NOT attached properly, result Vibrations that interfere with the music and all sorts of other funny sounds ......


~Nemo~

If your box isn't strong enough, it will literally burst open, the sub won't have any internal back-pressure, and you'll rip the speaker right off the magnet. Support the box and you should be straight. Why are you using fiberglass?

Now dont go just by my word, I dont really know what I'm talking about here but I think they mean you need to add some support to the box so when it vibrates it doesn't break.