JBL JRX125 is a dual 15" speaker gives more low-frequency performance while maintaining the simplicity of a single-box system. The JRX125 is actually a "quasi three-way" design. This means that the upper woofer covers lows and mids. The bottom woofer uses a lower crossover frequency and covers only lows, acting as a built-in subwoofer. So you get the extra low-end of a dual 15" rig while maintaining the superior mid-frequency performance of a single driver system.