The PB13-Ultra measures in at 22.5 inches tall by 20.5 inches wide by 27 inches deep. The PB12-Plus, on the other hand, is 22 inches tall by 19.75 inches wide by 25.2 inches deep. The PB13-Ultra weighs 155 pounds, while the PB12-Plus weighs 127.
SVS manufactures three high-end ported box subwoofers designed to be used with home theater systems. Two of these subwoofers, the PB12-Plus and the PB13-Ultra DSP, or digital signal processor, feature similar designs and components with a few significant differences. The main differences come in the size of each unit and the woofer, subwoofer and amplifier included with each unit.
Both the PB13-Ultra and the PB12-Plus come with a black gloss or full-veneer black oak finish, and both have a front-firing woofer. The PB13-Ultra comes with three front-firing 3.5-inch high-flow flared ports and three dense-foam port blockers, while the PB12-Plus comes with three front-firing 3-inch high-flow flared ports and the matching port blockers. Both subwoofers also have 20Hz, 16Hz and sealed tuning modes.
The woofers included with the PB13-Ultra and PB12-Plus feature many of the same components, with a few differences. The PB13-Ultra features a 13.5-inch underhung "Ultra" woofer, and the PB12-Plus has a 12-inch underhung "Plus" woofer. The PB12-Plus features a single composite-layered, linear-roll long-throw spider while the PB13-Ultra features two 9-inch, composite-layered, linear-roll, extreme-excursion spiders. Other than these differences, the two woofers are identical.
The amp specs of the PB13-Ultra and PB12-Plus are also similar, with one significant difference. The PB13-Ultra features a STA-1000D Sledge amplifier, capable of outputting 1,000 watts into 6 ohms. The PB12-Plus features the STA-800D Sledge amplifier, which outputs 800 watts into 4 ohms. The rest of the amplifier specifications are the same across both models.