When you are looking to buy car speakers, one of the most expensive choices are the subwoofers. Although most speakers will come in matched pair sets, subwoofers are usually sold alone and based on size, quality and whether or not they are already installed in a specially built box.
8 inch Subwoofers: The smallest available subwoofer speakers are the 8 inches in diameter ones and generally cost between $20.00 for the least expensive up to $350.00. If you are using 8 inch subwoofers, it is suggested to use them as a pair.
10 inch Subwoofers: 10 inch subwoofers, often a popular size, as pairs generally run between $25.00 and $750.00 each.
12 inch Subwoofers: 12 inch subwoofers go up a little in price, and run between $35.00 to $1000.00 each.
15 inch Subwoofers: 15 inch subwoofers are the most popular size for hip hop, rap and techno music, and sell between $50.00 and $1700.00 each.
18 inch Subwoofers: 18 inch subwoofers are the largest available, but not the most popular choice. This size is much harder to find, and usually costs between $100.00 and $400.00 each.
Subwoofers can be the real backbone of your car audio system, so that when you buy car speakers it pays to spend a little money on them. If your subwoofers are cheap knockoffs, your music will reflect it in the sound quality.
With the proper research, you may be able to pick up subwoofers second hand from places like eBay, craigslist, used car dealerships, and pawn shops. But make sure you know what you are looking for, or take a knowledgeable friend along to judge whether what is for sale is worth the price.