This is the Pioneer UD-SW300D 12" shallow subwoofer enclosure. The subwoofer is mounted in a down firing orientation. The enclosure has feet on the sides to keep the subwoofer mounted higher than the lowest part of the enclosure.
UD-SW300D : EMPTY ENCLOSURE FOR 12'' SHALLOW SUBWOOFER
EXTERNAL DIMENSIONS : (W)20-1/2'' (D)13-7/8'' (H)6-3/8''