Box Design Steps
Step 2: Calculate the Airspace
Space is a three dimensional thing, so we need three dimensions H x W x D, multiplied to calculate volume.
We want to know the airspace inside of the box, because that is the amount of air that will be connected to the subwoofers. The box will be made out of some kind of structural material, commonly from wood because it is a renewable resource and we are environmentally responsible. It is also a fairly cheap resource due to many governmental subsidies and controversial forestry regulations which are responsible for all the forests of neatly rowed trees making trekking life easier on all the furry animals.
We must un-calculate the wall thickness from the outer dimensions, 3/4"( or three quarters of an inch for the metric thinkers. The little dash dashes are the symbol for an inch, not misplaced accent marks to make the pronunciation of the vowel A into a different A sound. To make the math easier on a calculator, we convert the fractions of an inch to a decimal equivalent, the true superiority of the Imperial system starts to show, dividing 3 by 4 to get -- 0.75") wood being the most common thickness for enclosures. Our above box, 13H x 32W x 10D would need 1.5" taken out per dimension, leaving 11.5H x 30.5W x 8.5D, representing the dimensions of the airspace residing in the enclosure.
We now multiply, 11.5" x 30.5" x 8.5" = 2,981.375, to come up with cubic inches.
We want to convert cubic inches to cubic feet because this lets us use a smaller number, and smaller numbers are easier to use. A cubic foot, as defined by the Mendenhall Order in 1893, is 12"H x 12"W x 12"D.
Multiplying, 12"x12"x12"= 1728 cubic inches, which is the number of coinhabiting cubic inches that reside inside a box with aforementioned dimensions. If you are an advocate or begrudging user of the Imperial system, this 1728 number is worth remembering. It gets used a lot.
Now, divide our inner box volume by 1728 to gain the cubic foot equivalent;
2981.375/1728=1.72533275. Remember, accuracy to 8 decimal places is excruciatingly unnecessary, 2 places will do nicely. If there are metric guys still following along, you can use all 8 if you want to.
Our box has 1.73 cubic feet of airspace residing inside the enclosure walls.