How to Calculate Speaker Box Air Space

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, based on the size, in the owner's 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 percent.

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, which is 12 x 12 x 12, or one cubic foot in inches. That is the number you want to know for the airspace needed for your speaker.