Made by Harman, the JBL BassPro SL is an under-seat subwoofer with the type of performance I've come to expect from Harman. The tight bass fills out a mix without dominating and it features a bigger sound than other under-seat subs. However, it's also the most expensive powered car subwoofer I reviewed by over $50. The performance, though very good, simply isn't enough to justify the difference.
With a market value at $255, the JBL BassPro SL is expensive by comparison to other powered subwoofers. That said, if you considered the cost of purchasing a subwoofer, amplifier and enclosure separately, it's still a good value and you're probably not going to be able to fit it all under a seat. In addition, the BassPro SL is identical to the Infinity BassLink SM in every way except color and brand, but the Infinity costs around $170. (Both are made by Harman.) So, if you want the performance but don't want to pay for it, the Infinity under-seat sub is the better option. However, it's worth noting the silver enclosure of the Infinity is a bit too eye-catching, making it far more likely to be stolen.
The BassPro SL earned an A- grade for the overall performance. Along with the Infinity BassLink SM, it was the best performing under-seat subwoofer. The performance loses some of its tightness near the maximum levels, but this is common with most subwoofers and was minor compared to other under-seat subs. Overall, the performance was mostly comparable to the Pioneer TS-WX1210A, a 12-inch car subwoofer. It fills out the mix very well.
The size of the subwoofer's sweet spot (the point where the sub’s at its best performance) earned a B+ grade. While the size doesn't compare to the 12-inch powered subwoofers I tested, simply because the 8-inch woofer can't move as much air, it's the biggest bass I experienced with an under-seat subwoofer. In fact, since the woofer is so much closer to your body (literally beneath you) than a trunk-installed enclosure, the size difference is negligible. The only difference is in how much the bass travels from the car. If you're stuck in traffic, for example, the JBL BassPro SL is less likely to be felt by the other cars.
The controls of the BassPro SL are excellent, receiving an A for ease of use. With six controls (three dials and three switches), you can really dial the subwoofer into your car's acoustics and your personal preferences. The crossover dial allows you to tune the subwoofers performance between 50 and 120 Hz. The knobs are easy to grip and adjust, and the control panel is on the long size of the rectangular casing, making it easy to access. The only downside is the lack of a remote. It has a port for a wired remote, but the remote is optional and must be purchased separately.
All under-seat subwoofers are compact, but the JBL BassPro SL is one of the most compact. It features dimensions capable of fitting under most seats without any trouble. The Kenwood KSC-SW11 is smaller, but doesn't have the performance to match.
The JBL BassPro SL is a very good under-seat car subwoofer. In fact, it's identical to the Infinity BassLink SM, my pick for the best under-seat subwoofer. The biggest difference is price, though I prefer its black enclosure over the silver of the Infinity. The BassPro SL is outpriced by every powered subwoofer I reviewed, and while the performance has the quality and size to be a great option, the Infinity BassLink SM is the same subwoofer, but at a much lower price.