2. A speaker that varies in size usually from 8" to 32". The most popular size is 12". They are made to put out the low end of the audio spectrum. They make the low end a.k.a. bass more noticeable and louder and smoother. Playing them loudly is also known as subwoofing, and if your not careful about where you do it, it will make other people mad. Subwoofer's are a great way to attract someone's attention, but just keep in mind thats not always a good thing.
I had my subwoofers working hard to get this girls attention, but at the same time I attracted someone else's attention and it was only a few seconds before I saw the blueberry's and cherry's in my rear view mirrior.