Reviewing the QSC KS118 Powered Subwoofer with Loren Alldrin

The Church Production Podcast

Review: QSC KS118 Subwoofer Review

By Loren Alldrin

Though speaker history reveals a few excursions (pardon the pun) into bass drivers larger than 20 inches in diameter, the 18-inch subwoofer has been the "big dog" of sound reinforcement for decades. Wrapped in enclosures of all shapes and sizes, the 18-inch driver has proven itself to have the right balance of size, extended low-frequency response and cost. Single 18" subwoofers, like QSC's new active KS118, are a staple of compact and mobile sound systems everywhere.

The KS118 has a single direct-radiating, 18-inch woofer that uses electronic filtering to discard unwanted mid and high frequencies. This is in contrast to the smaller KS112 and KS212 subwoofers, which use a serpentine bandpass enclosure to acoustically roll off high frequencies. The end result is the same--lots of acoustic energy across a tightly controlled frequency range. For the KS118, that frequency range is about 35 Hz-110 Hz (-10 dB).

Same, yet different

The subwoofer is similar in size and shape to its predecessor the KW118, although the new cabinet's orientation is rotated by 90 degrees. The KW118 had 2,000 watts peak output; the KS118 bumps this to 3,600 watts. That translates to a peak SPL rating of 136 dB for the KS118. That's an impressive amount of bass, and I doubt many Sunday morning services will need more output than one or two of these boxes will generate. Come nightfall, a pair of these subs should cover the bottom end for full-blown concerts in venues up to several hundred seats.

We've come a long way from the days when a subwoofer was little more than a big driver in a big box. The KS118's onboard processors and amp section replace a bunch of outboard gear, all controlled by a panel safely nestled between casters and skid strips. The interface consists of a large selector knob, a few buttons, and a nice bright display. Menu options allow you to select from three different crossover points, engage Digital Extension and Excursion Processing (DEEP) mode, control delay and configure the cardioid processing. You can even save and recall presets. I never needed the subwoofer's manual, because the menu system is intuitive and easy to navigate.

The KS118's DEEP mode extends its low frequency response (with filtering, not synthesis) at the expense of a few dB of maximum SPL. Because few church venues will need to run the subs anywhere near their maximum SPL, I think this is a trade-off most will be willing to make. I engaged DEEP mode and never turned it back off. It makes the subwoofer's low frequency response even better, and doesn't compromise its tight, controlled sound.

I was eager to try the KS118's cardioid mode, which works with two subs pointing in opposite directions. When enabled at the control panel, bass output to the rear of the pair is decreased by as much as 15 dB, depending on configuration. This keeps bass energy from being wasted behind the stage outdoors, and should help reduce low-frequency clutter indoors. In real world testing, my results were mixed. I was able to hear a definite reduction in bass behind the cabinets in outdoor settings. Indoors, with bass filling the room, it was harder to discern a significant improvement in clarity or accuracy. Users should try cardioid mode in their venue--they can always fall back to the normal omnidirectional mode.

Close-up on the cabinet

The KS118 has large rubber feet on two sides, allowing it to be laid flat or stood upright. Both of these orientations put the casters, control panel and inputs on the back side. The cabinet has indentations opposite the feet for secure stacking of multiple cabinets. Despite its size and the sturdiness of its cabinet, the KS118 is surprisingly light and easy to maneuver. More than once, I found myself lifting the whole speaker up by one handle when trying to fine-tune its position. The casters are of high quality, making it an easy (and smooth) operation for one person to roll the speaker around.

From an ergonomics standpoint, I only struggled with the placement of the two recessed handles. When tipping the speaker on and off its casters, I often found myself reaching for a handle on the side where one wasn't. I can picture a group of designers arguing about which sides to put the handles on, and in my opinion they got it wrong. Granted, I was often wrangling the subwoofers by myself. Perhaps the handle placement would make more sense when being moved about by two people.

Pumping over 3,000 watts of power into a single driver definitely gives it a workout, and QSC was wise to give the KS118 thermal and excursion protection. QSC believes the KS118 can handle the current, and they stand behind the sub with a six-year warranty. The reliability of a subwoofer really hinges on the quality of the actual driver. QSC cut no corners in this area, loading the KS118 with an Italian-made B&C driver. Bravo, QSC.

Compared to a full range speaker, a subwoofer's job is pretty straightforward. It has to reproduce an octave or two competently, building a foundation on which the rest of the music sits. Within the bounds of this simple job description, the KS118 sounds fantastic. At lower volumes, the KS118 adds the fullness and warmth you expect from a well-behaved church subwoofer. At higher volumes, the KS118 puts on its club/concert attire and brings the excitement. It submerges you in that powerful, encompassing bass you experience viscerally. Great fun.

--BIO--
Loren Alldrin is a regular contributor to Church Production Magazine.