The individual side, top and bottom and front/back panels of an enclosure must be properly measured prior to cutting. Once assembled, the panels form the enclosure for the driver. Care should be taken during this process, since creating the proper enclosure volume is more critical to subwoofer performance than any other element of the enclosure design and build process.
All subwoofer drivers operate via their Thiele-Small set of specifications. These specs define the enclosure volume, power handling, and performance properties of the driver. It is critical to measure the panels comprising the enclosure prior to building it, or the dimensions of a finished enclosure to determine the internal volume. Placing a subwoofer driver in the wrong-sized box results in poor performance and often damage.
The simplest subwoofer enclosures are square or rectangular. Measure the height, width, and depth of an off-the-shelf enclosure the determine the internal airspace. Multiply the three figures together, and then divide the total by 1728. This tells you the internal volume of the enclosure, which you must be armed with to determine if your existing subwoofer will operate properly inside.
Also known as hatchback enclosures, wedge-shaped boxes are also used behind the seat in trucks. Finding the volume inside these enclosures is accomplished by measuring the height, depth, and 1/2 of the base. Multiply these three figures together to determine the internal airspace.
Subwoofer boxes that are too small tend to increase the "punchy" properties of a subwoofer. However, this also tends to create excessive midrange energy, perceived as "boominess" or a bloated sound. Enclosures that are too large do not place the proper amount of back air pressure on the subwoofer driver, causing it to move excessively while playing. Although this creates more bass, it potentially also causes the driver to potentially move beyond its maximum excursion limits.
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