Single 15 inch subwoofers are great for most medium to medium-large DJ and pro audio sound reinforcement needs. They are small enough to be transported and setup by one person, yet they are powerful enough to belch out plenty of gut-shaking low end.
Single 15 inch subwoofers can be self-powered, with a built-in amplifier, or they can be passive, fed by an external power amplifier. They can also be of two different designs, direct-radiator or horn loaded. As always, if you are going to the expense of purchasing a set of subwoofers for your pro audio sound system, save enough money in your budget for a decent electronic crossover. This will help you get the most out of your system, and bring a wide smile to your face, and all those who attend your gigs!