JBL are famous for their quality speakers and users of their products won't be surprised to discover that this self-powered subwoofer is excellent.
Weighing in at 500 Watts (at peak) and 300 Watts (RMS) this is a hefty piece of kit which provides excellent sound quality and a proper booming bass. I reall;y wish I could say that I own a pair of these babies but I don't. I've borrowed a friends set a few times and have been blown away with them. I really wish I could afford a pair but the lowest price I can find them for is just under £500 (maybe I should start saving). They are really easy to set up, with two XLR inputs or one 1/4 inch jack input. They also have two XLR outputs if you need to wire them up in a 'chain' of speakers (which is easy enough to do if you know what you are doing).
These badboys are not massive but they weight a fair bit, I've never actually weighed them but a bit of internet investigation shows that they weigh in at 89lbs. I also found the measurements, they are 23.5 inches high, 20.3 inches wide and 23.5 inches deep. Big enough to take up a fair bit of room in the boot of your car! The speaker has a hole in the top in which a speaker stand can be mounted to hold your main monitor/speaker.
Overall, I would say these are a very worthwhile investment.