9
CHOOSING A SPEAKER ENCLOSURE
This speaker is designed optimally for FreeAir applications, but will work well in a sealed or a ported
enclosure (see below)
SEALED BOX:
A sealed or acoustic suspension enclosure is easy to build and typically offers a smaller
size enclosure and greater power handling. It has the most predictable frequency and phase response;
the bass response will roll off slower than that of a ported design. Sealed boxes typically provide the best
musical detail and definition. A well-designed sealed enclosure will exhibit smooth frequency response with
excellent sound quality and great low bass extension. They also exhibit relatively accurate, punchy bass
reproduction for most types of music.
If a sealed enclosure is too large to fit into a specific area of a vessel, it is possible to decrease the recom-
mended box volume by using 1.5 pounds per cubic feet of low density, high heat specific box stuffing
material. PowerBass recommends Fiberglass, Dacron, Poly-Fill or long fiber wool for stuffing the enclosure.
(Decreasing the box enclosure however should not exceed 20% of the recommended size.) When using any
type of box stuffing material be sure that the subwoofer’s vented pole piece is clear from any obstructions,
since covering the pole piece will result in loss of bass and can possibly cause damage to your subwoofer.
The most important aspect of a sealed enclosure is to make sure that it is airtight and solid. If your enclo-
sure has any air leaks or if the panels vibrate or flex, you will experience a loss of bass output. Using glue
and some type of sealant (caulk) on all seams will ensure a solid constructed box without any air leaks.
VENTED BOX (NOT OPTIMUM):
Also known as a ported or bass reflex enclosure, this type of box is
almost as easy to construct as a sealed enclosure. This design however is more efficient and results in
an increase of bass output at certain frequencies. Although vented enclosure has an output advantage at
some frequencies, it also has a steeper rolloff, which will only affect bass frequencies below port tuning.
Air inside the port will move in phase with the subwoofer reinforcing frequencies above the F3 (-3dB point).
The SPL advantage of the vented enclosure comes from the fact that the effect of the vent tuning reduces
the excursion of the subwoofer near the tuning frequency allowing more SPL to be produced before the
subwoofer bottoms.
