The sealed subwoofer box is a better choice if space is extremely tight, but the ported subwoofer box will produce 3dB more output at the same power if you have the extra space to work with.
• The subwoofer box diy design project recommendations listed above are external dimensions which assume the use of 3/4" (19mm) thick material. If you are using 5/8" (16mm) thick material, subtract 1/4" (6.5mm) from each dimension. Do not use any material with a thickness of less than 5/8" (16mm) as this may compromise the rigidity of the enclosure.
• All subwoofer box volumes listed above are net internal volumes! Driver displacement, port displacement and brace displacement must be added to obtain the final gross internal volume. All enclosure dimensions above have already taken this into acount.
• When using two subwoofers in a common enclosure simply double the required volume and, in the case of a ported enclosure, use two times the recommended port(s). Likewise, when using three subwoofers in a common enclosure simply triple the required volume and, in the case of a ported enclosure, use three times the recommended port(s).
• We recommend the use of this speaker in a bi-amplified system using high quality satellite speakers and a high-quality amplifier. We do not recommend the use of this subwoofer with a passive crossover (coil), as this type of device will adversely affect performance.
Source: JL AUDIO 8W3/10W3 manual