The most common PA complaint we hear is “it distorts when we turn it up” — and surprisingly often the fix is not bigger tops. It is a subwoofer. Here is why, and how to choose one that matches what you already own.
Why a sub makes your whole PA sound bigger
Low frequencies eat amplifier power. When your 12” tops are reproducing kick drum and bass synth as well as vocals, most of their headroom is spent below 100 Hz. Hand that range to a dedicated sub with its own amplifier and driver, engage the high-pass filter on the tops, and two things happen at once: the bass gets dramatically fuller and the tops suddenly sound cleaner and louder, because they are finally free to do the job they are good at. One sub often improves a system more than two extra tops would.
Our pick: the FBT X-Sub range
FBT designed the X-Sub series as the purpose-built low end for the X-Lite and X-Pro tops we recommend in our PA speaker guide, and it shows in the details. The X-Sub 118SA puts an 18” driver and a 1200W Class D amplifier in a birch plywood cabinet good for 136 dB, reaching down to 38 Hz. The clever part is the rear panel: stereo high-pass filtered XLR outputs mean you run your signal through the sub to the tops and the crossover is simply done — no settings menu, no guesswork — while four DSP presets tune the pairing. Gigging with 10” or 12” tops in smaller rooms? The X-Sub 115SA gives you the same amplifier and features in a lighter 15” box.
When the dance floor is the main event
For DJs, clubs and anyone whose audience judges the night by what they feel in their chest, the QSC KS118 is the benchmark single-18 — and the twin-12 KS212C adds a party trick: cardioid bass from one box, throwing low end at the dance floor instead of out the back wall at the neighbours. Noise-limit venues love it. Already invested in JBL tops? The EON718S and touring-grade PRX918XLF keep the system one brand and one app.
One sub or two?
Start with one — centred subs couple with the floor and often outperform a hastily placed pair. Add the second when you need more output or wider coverage, not by default. And whatever you buy, use the high-pass on your tops; it is the free upgrade hiding in the settings menu.
Tell us what tops you run and what you play, and we will match a sub — and set your crossover points before the box leaves the shop.