When building an enclosure for your speakers it is important to calculate the proper airspace inside your box. The proper airspace will allow your speaker to play efficiently and sound the way the manufacture intended. The bigger the speaker, the more airspace it will need to sound right. So a 12-inch speaker will need more airspace than a 10-inch speaker. To build the correct enclosure for your speakers, you must calculate the airspace for your box.
Determine how much airspace you will need for your particular speaker. Most manufacturers will tell you the airspace needed for their speakers, depending on the size. You can find the recommended airspace in the speaker's owners manual. If that information is not available, here is a list that will get you close.
6 inch drivers: 0.3 to 0.4 cubic feet
8 inch drivers: 0.6 to 0.8 cubic feet
10 inch drivers: 1.0 to 1.5 cubic feet
12 inch drivers: 2.0 to 3.0 cubic feet
15 inch drivers: 5.0 to 9.0 cubic feet
Increase the airspace needed for volume displacement. The speaker, braces, ports--anything inside the box--will take up airspace within the enclosure. A good rule of thumb is to increase the volume needed by 20 per cent.
Calculate the volume of the enclosure you are building. You can do that by taking the height x width x length. To make it easier, use inches when calculating the volume. If your enclosure is 12 inches in height, 20 inches wide and 15 inches deep you would multiply 12 x 20 x 15 and that would give you your total volume in cubic inches.
Divide the number you got from Step 3 by 1728. Why 1728? That is one cubic foot or 12 x 12 x 12. Dividing 1728 for your figure in Step 3 will convert from total cubic inches to total cubic feet. That is the number you want to know for the airspace needed for your speaker.