airspace?

how do you figure the airspace on a fiberglass boxcml

Got Math? L x W x H divided by 1728 = cubic feet. Irregular shapes can be difficult but not impossible to calculate. Your sub box isn't going into space, you can be off a little here or there. Plus or minus 5% of the recommended volume won't change anything. You might be able to get away with 10%. Adjust the box volume due to the displacement of the basket and magnet. Experiment with polyfill or dacron. Both can help the driver to see a tad bit more airspace than is really there.

Yea as audiocableguy said, he was firm in his explanation.  Plus that sticky on packing peanuts I think is crap as packing peanuts are quite big and break.  I found the cheapest thing to use to find volume in a FG box is rice.  I pick up rice for $0.99 for 5 pounds at my local super market, and just recently bought 50 lbs. for my enclosure calculations.  Remember, and always remember when calculating volume to accomodate for driver displacement, bracing, supports, etc. etc.

Like they say, water, Packing peanuts, Actual peanuts, as long as you can measure it. Remember that the volume of the cone and basket of the sub itself will count. This is not an exact science, it is a car sub woofer, not an electron microscope. The peanuts measurement is just to check that you are not way off. In reality where you put the sub etc will contribute a lot to the sound, you can also adjust it a lot with fill. My advice don't sweat the volume too much, but concentrate on the f'glass lay up - thats the hard part. Fibreglass tuturial Fibreglass wheel well sub box