Van De Graaff

How Big Can the Enclosure Be?
Do you want to take up all the available space inside your car/truck/van/sport-utility? Or are you looking for something that is compact enough to be removed easily when necessary? These are important questions you must answer before beginning your project. First, measure out the area you’re interested in placing the subwoofer enclosure. Use a good-quality measuringtape (not your mom’s cloth tape from her sewing kit) to determine the MAXIMUM height, width, and depth of your area. Height is the measurement up-and-down, width is the measurement from side-to-side, and depth is the measurement back-to-front. (We’ll assume you’re using English standards (inches, feet, yards) when measuring, and our example calculations will be done using these standards.) Onceyou’ve determined your maximum external dimensions, it is a good idea to start drawing out your enclosure on paper. If you make a mistake, you can simply erase it and start again, versus cutting the wood right away and discovering you have just made something resembling a large toy box. Since you know what the external dimensions can be, we’ll move to the next step!

Tech Tips
Measure the availablespace in your vehicle, making sure to draw out your design first, and ensure the enclosure will fit through any openings. Things to Remember There are no special size limits. (You do, however, want to avoid long, round enclosures in excess of 72" - if the airspace in the enclosure is long and stretched out, the woofer cannot couple to all of the air. When this happens, the air at the end of theenclosure becomes its own separate moving mass and can mistune the enclosure dramatically.) Re-measure the area you’re loading the enclosure into, and make sure the box will fit in through any openings. Nothing is more frustrating than building the perfect enclosure only to find it won’t fit through the trunk opening.

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RFTECH: ENCLOSURE

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How Do You Figure theDimensions?
It is extremely important to know the internal volume necessary for the subwoofer you’re using (also known as “box size”). Most manufacturers will tell you what the ideal-sized enclosure is for their woofers, and we’re no exception. Since not all subwoofers require the same amount of airspace, different lines of the same brand of woofer can have completely different enclosure sizerequirements. As a general rule of thumb, making the enclosure too small will result in a lack of low-end bass response, and if it’s too large, you won’t have as much output as you could and the woofer’s power handling will suffer. (If you’re unsure of the recommended enclosure size for your Rockford Fosgate woofers, please visit the library section at www.rockfordfosgate.com.) Calculating the correct boxsize is easy if you just remember a few simple formulas and calculations. The key to calculating internal box dimensions is a basic understanding of volume: Cubic volume is derived by multiplying each of an object’s dimensions (height, width, depth) by each other. For example: If you measure the internal dimensions of a rectangular object (like a subwoofer box) and its internal height is 12", itswidth is 24", and its depth is 12", and then multiply those dimensions together (12" X 24" X 12"), then you come up with a volume of 3,456 cubic inches. (See Figure A) Enclosure volumes are never listed in cubic inches, so it is necessary to convert from cubic inches to cubic feet. (A cubic foot is no more than 12" X 12" X 12" or 1,728 cubic inches.) So, to convert from cubic inches to cubicfeet, simply divide the volume in cubic inches by 1,728. In the case of our example above, this would be 3,456 divided by 1,728, or 2.0 cubic feet internal volume. Since we know that the woofer will take up space in our enclosure, we will need to add for that volume, called its displacement. Woofers, ports, and internal bracing (covered in the Advanced section of our Enclosure pages) will all have a...