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Can I used 3x expanding foam to take up cu. ft. in sub box?

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  • Can I used 3x expanding foam to take up cu. ft. in sub box?

    So I built a fiberglass sub box for my 350z to fit under the strut bar knowing it would be too big. But, now I gotta figure out a way to remove .4 cu. ft. I could obviously just fill the box up with wood blocks but I'm not trying to make a boat anchor. So instead I was thinking I could just put some triple expanding foam in there. Not sure if this will work to effectively decrease the volume of the box though? Need some help.
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  • #2
    I'm not an expert on these boxes, but I have worked with the foam. Although I can't provide a nice, clean "Yes" or "No" answer, a couple of things come to mind:
    • That expanding urethane foam is really hard to control, although it does stick to almost anything. It would probably be best to put in too little and add a second area after re-measuring.
    • Although the foam develops a skin, will the surface be enough to withstand the constant battering of the sound waves, or will it eventually degrade? If it would, maybe a layer of glass and resin would toughen it.
    • Did you allow for the volume of the speaker?
    If just enough is really good, then too much ought to be perfect.

    2006 Scion xB with in-dash Atom & Lilliput 889GL -- Worklog at