Pros: Good clean bass, small size, flexible connection options.
Cons: Fixed length wire on remote, lower output than larger subs, 120 hz highest crossover frequency
I recently purchased the Kenwood KSC-SW1 to use in my 2003 Honda Odyssey minivan, along with a Pioneer head unit and Alpine amplifier (I've kept the stock speakers for the moment). The stock Honda system has widely come under criticism in Odyssey groups for its poor sound; I found it usable but lacking in treble and (especially) bass. I decided to replace the system and add an external amp and subwoofer.
Because this is a minivan, using unenclosed subs is out of the question - there's nowhere to mount them. I also had another requirement: it had to be small enough to fit between the front seats. I didn't want the sub in back because I may be listening to music while I'm driving, but the kids will be in the back playing their Gameboys, and don't want to hear it (quite a change from when my parents were always asking me to turn my music down :-); also, I need to be able to convert to a cargo carrying van for those trips to Lowes. This requirement narrowed the field down to just a few subs; besides this one there was the Kenwood W00x and the Clarion SRV303; however, I had read reviews of both and was unimpressed. I was originally hoping to install an Infinity Basslink, but alas, this was way too tall.
The KSC-SW1 seemed ideal, although I had my doubts about its small driver size. When I received it, I was also concerned about the small cabinet size and light weight. As it turns out, my fears were mostly unfounded. The sub goes quite low - low enough for me at any rate - without distorting. However (and this is where the limitations of a 6.5" driver come into play), it is not capable of the high SPLs you'll get from a 10" or larger woofer. Part of the problem is likely due to the size of the space. The interior volume of a minivan is probably 3-4 times that of a 2-seater pickup or sports car, where it would really shine. At reasonable (actually, more than reasonable - way louder than my wife would tolerate) volumes, it works beautifully. And since this is really my wife's car, and I rarely drive it alone, the SPL limit is not a huge disadvantage.
Kenwood rates the sub amp at 75 watts output, and the amp seems well matched to the speaker.
Installation is straightforward. You can use either line- or speaker-level output to connect to the sub. Kenwood only provides a low-pass crossover, so I recommend using the line level inputs if possible and filtering out the low level signals to your main speakers with either a separate passive or active crossover, which will decrease distortion if you're running them at the limit. This is how I connected mine - my Pioneer head unit has dual pair RCA outputs that can be configured for subwoofer and main speakers (I use the built in amp for the rear speakers) with a (selectable) crossover frequency of 80 hz. This turned out to be a good match for my main speakers.
One potential problem for a few people is that the highest crossover frequency for the sub is 120hz, and there's no way to disable it. This means you cannot cross over higher than that, even if you use your own active crossover. For most vehicles this won't be an issue, but if your car only has 3 1/2" dash speakers, you may want to cross over at 150 hz or even higher, which you can't do. And if you want to cross over at 120 hz exactly, you should disable the low pass filter on your crossover and run the Kenwood from a full range output, otherwise you'll end up cutting out a lot more than you intended (you'll be doubling the amount of filtering).
There is a wired remote control on a long cable which allows you to adjust level, crossover frequency and phase. I found this remote to be of limited usefulness; once I have a sub adjusted I leave it alone. It would have been nice if Kenwood had provided an option to mount this remote directly on the sub; however, it is a captive wire on the remote end and and uses a 6-pin RJ11-style plug on the other; if I can find one of those maybe I can cut the cable shorter; otherwise I'm going to have a bundle of cable under the seats. I understand Kenwood's reason for doing this; for a rear installation you need an easy way to make adjustments. But an easy way too shorten it would have been nice.
The addition of this sub has improved the sound of my system dramatically. While there's no way for me to tell what improvements were made by the new head unit, the new amp for the front speakers, or the sub; I can now hear clean bass that I was only used to hearing from my home system, which uses Infinity Kappa 8s as its main speakers. Due to reducing the requirement for the main speakers to produce low bass, they sound much clearer as well; in fact, their sound has improved so much that I may keep them.
In conclusion: if you're not looking to cruise the local strip with your stereo cranking and the windows open so everyone can hear what you're listening to, this sub is definitely worth a look.