http://www.mackie.com/products/s410s/index.html

Ask any bass player and they'll tell you 10" speakers offer quicker attack (transient) response than a single 15" or 18". In our never-ending quest for the ultimate subwoofer, we turned to the gurus at Eastern Acoustic Works (EAW), who were highly instrumental in the design of our new S400 Series loudspeakers. This new design philosophy, which employs multiple smaller drivers versus a single 15" or 18", is carried forward in the S400 Series subwoofer. We replaced the single 18" found in most small venue sub cabinets with four 10" transducers, creating the Mackie S410s Subwoofer—the perfect companion to our S408 full-range loudspeaker. This new configuration translates into a punchy, tighter bass pattern, and lots of it! 

BIGGER AIR MOTOR
Let's look at a typical subwoofer; the 18" speaker offers extremely slow transient response, and requires a massive amount of power to get the job done. We threw out the 18" speaker in favor of four 10" drivers, which provide substantially more surface area than the 18-incher, creating ample punch and tight, more focused low-end. And four 10" speakers are much more efficient. More surface area =

more air movement = more thump!