July 2003 Reviewed by John Potis	ACI Force Subwoofer

Description Model: ACI Force Price: $749 USD Dimensions: 16.75"W x 13.5"H x 12.5"D Weight: 48 pounds Warranty: Five years parts and labor (fully transferable) Features MDF construction with internal bracing Stackable design Volume control Speaker-level or line-level (RCA) inputs 250W (continuous) discrete amplifier Inputs for mono or stereo operation

Features (cont'd) Adjustable crossover (35-250Hz, 24dB/octave increasing to 36dB/octave) Theater-direct input High-pass RCA outputs (second-order filters set at 100Hz for left and right output) Current-sensing feedback loop to reduce distortion Protection circuitry senses and limits excessive input levels Designed to be left on (draws less than 10W at idle) Black textured cabinet with solid hardwood endcaps Available in clear or black lacquered oak (clear lacquered cherry, rose walnut, maple, and mahogany available at slightly higher cost)

I can’t think of a single component in a home-entertainment system that comes tethered to more fuzzy logic, or that engenders more fundamental misunderstanding, than the subwoofer. I’ve seen some pretty silly statements, such as "People who like subwoofers are too easily pleased." Take a look at many megabuck speakers and you’ll notice that many of them are four-piece (or more) systems with separate bass enclosures (usually two of them) alongside nearly-full-range speaker columns.

One of the most successful and longest-running speaker series of all time is the Wilson Audio WATT/Puppy, which is fundamentally a superbly executed monitor speaker sitting atop an equally well-executed passive subwoofer. What’s so hard to grasp here? While not all of us can afford such utopian efforts, there’s no reason we can’t scale back our expectations of bass quantity and apply the same principles to get greater bass quality.

Why all the prejudice against subwoofers? I suspect the main reason are fundamental lacks of good information about what constitutes a good subwoofer, and how best to situate it. A subwoofer is an important part of the speaker system, and its positioning is of no less importance than positioning the main speakers. Formulas are available that can do a wonderful job of computing the best location for your subwoofer, but trial and error works, too. Just do not assume, as is often stated in marketing propaganda, that a subwoofer will work well anywhere you see fit to drop it.

As for what makes a subwoofer a successful design, well, just as bass performance varies from speaker to speaker, so too will subwoofer performance. Some may think you can tell what you need to know about a subwoofer’s performance from simple SPL measurements -- i.e., how loudly it plays. There may be some truth to this if all you’re after is loud movie effects, but I believe that when even people in the SPL-above-all-else camp are exposed to a good subwoofer, they’ll hear details in effects that poorly performing, poorly integrated subwoofers omit. For both music and home theater, the requirements for a good sub should be the same.

Nuts and bolts

The Audio Concepts, Inc. (ACI) Force ($749) is a smallish subwoofer that won’t dominate most rooms, but it’s no flyweight. The bottom of the cabinet, where the driver is mounted, is a full 2"-thick slab of MDF. The top panel is 1" thick, and the sidewalls are three quarters of an inch thick before ACI attaches two nicely finished half-inch side cheeks. The 10" driver is an ultra-stiff doped-paper cone custom-made for ACI in the USA, with unusually heavy-duty surrounds enabling nearly a full inch of travel. ACI is equally proud of their custom-built 250W amplifier, which spent over a year in testing and design.

Basically, the amplifier is the same one used in their more expensive Titan II LE subwoofer, with the addition of what ACI describes as a "personality card," custom-designed for the Force’s size and design parameters. Mike Dzurko, founder of ACI, tells me that, unlike most subwoofer amps, the Force’s is a full-bandwidth design incorporating a toroidal transformer and high-quality caps and resistors. As in the Titan, some limiting is used in order to protect the subwoofer from being overdriven, which, in conjunction with the heavy-duty build quality, should mean that the unit will likely be overdriven only by a lightning strike or abusive test signals.

A versatile musical performer

In the months I’ve had the Force in my home, it has seen duty in two different systems and with a multitude of speakers -- some notoriously difficult to mate with subwoofers. For instance, I was able to pair the Force with my Silverline Sonata IIs to a more successful degree than I’ve ever been able to achieve with any other sub, for true 20Hz extension. I was able to augment the Silverlines’ bass extension while avoiding the slurring of bass that results from too much speaker/subwoofer overlap.

Likewise, I was able to match the Force with a pair of Magnepan MG3.6Rs -- a dipolar panel speaker with a very different bass signature from that of the Silverline. Known for its speed and articulation down low, the MG3.6R can be very difficult to mate with a sub, but the Force succeeded in a chameleon-like effort to add more meat and deep-bass articulation to these excellent speakers. The same can be said for Magnepan’s MG1.6QR and even their MGMC1, after some changes in the Force’s filter points and slopes. This success indicates considerable performance flexibility on the Force’s part.

In the theater

In my home theater, the Force saw a more limited group of stablemates. Speakers were the Magnepan MGMC1 and MGCC2 speakers, but rather than using the Force’s own filters, I advanced them to their highest values (to effectively get them out of the way) and allowed the Outlaw ICBM to handle all bass filtering and distribution duties. The fact that a single ACI Force subwoofer was replacing two Velodyne SPL-800 subs should have had the effect of hamstringing the Force from the start.

It did. Though the ICBM allows the option of combining the stereo signal and sending dual-mono bass signals to two subs, it also allows for sending it along to a single sub. Whether the credit goes to the preservation of dual bass signals or to the fact that two properly placed subwoofers offer a continuity of room coverage that a single sub cannot, the fact is that I was subtly aware of a slight decrease in bass smoothness in the theater room that was not in evidence in the music room. An argument for the use of two smaller subs rather than a single larger one? I’d say.

That slight caveat to its overall system performance aside, the Force did a spectacular job in my system. After insertion of the Eagles’ Hell Freezes Over DVD, I did the Force a disservice by choosing the PCM soundtrack and cueing up "Hotel California." Compared to the DTS track, the PCM track has a very different-sounding bass line -- one considerably looser, woollier, and with less detail. The Force reproduced the deep bass drum as well as I’ve ever heard it in my room. Woolly? You bet, but reproduced with better composure than some other speakers or subwoofers I’ve used. In fact, switching between the two soundtracks provided a good tutorial in the importance of quality bass reproduction. The DTS track sounded much better: tighter, more highly damped and detailed, albeit with less power -- and much more enjoyable. The Force was more than capable of highlighting the differences involved.

Armageddon is one of my favorite subwoofer-evaluation movies; between the music soundtrack and the onscreen effects, there’s much for a subwoofer to sink its teeth into. The film has two separate and distinct levels of effects. A fairly high level of deep-bass drone accompanies much of the movie: a combination of the sound of machines and an unstable asteroid. And even when listened to at unusually high (for me) levels, the deafening drone was frequently shattered by the much more concussive explosions. To be successful with this movie, a subwoofer must be able to instantaneously shift from high gear to hyperdrive. There were times when the Force so successfully reproduced the high levels of sustained bass activity that even I had my doubts whether it would be able to jump to the transient-rich and intensely powerful explosions -- the kind that instantaneously energize the room. The Force never let me down. I watched many movies with the Force, and most of the time I was able to forget the fact that there was a new component in my system.

Another subwoofer demo favorite is Mission: Impossible 2. During its stay, I never really seemed to test the subwoofer’s dynamic capabilities, so I really cranked up M:I2 to see if I could make the Force blink. It didn’t. The opening scene’s crash of the jet liner sounded fantastic, and really rocked my room. Ditto the Spanish dance scene -- particularly the slow-motion portion. The powerfully pulsing bass not only did its job of impacting me, it also caused various things around the room to come alive in syncopating rhythm.

One of my favorite subwoofer demo DVDs is U-571. It’s a real woofer workout, particularly when the German destroyer is dropping tons of depth charges over our heroes’ commandeered German submarine. Here the Force earned its name, with loud and room-shuddering effects. Speaking of submarines, no demo is complete without a showing of The Hunt for Red October. This movie contains more restrained levels of bass, almost from beginning to end, and the Force did a heroic job of never overplaying the more subtle effects, such as the constant bass turbulence resulting from the submarine’s rivets popping. Nicely played.

Comparison

I’ve already talked about how the single Force didn’t give me the smooth frequency response I’ve been able to achieve with stereo subwoofers. But this was the only aspect of performance that felt compromised when I replaced my Velodyne SPL-800s ($1099) with the single ACI sub. While the Force is fairly small, it did outsize the similarly priced Velodynes by a good margin. But what you give up in compactness the ACI makes up for in additional bass extension: The Force can extend all the way down to 20Hz, as compared to the Velodynes’ 28Hz

Conclusion

ACI’s design philosophy has always been to create not the highest quantity of bass, but the highest quality. For more than ten years, the Titan series (a former reference of mine) has earned strong recommendations as a sub that will seamlessly blend into any music/HT system. Now the Force joins the Titan as a very capable yet more affordable (and smaller!) alternative. Despite what the assemble-a-system-by-the-numbers gang would have you believe, my experience is that a single Force will play more than loud enough for most listeners. Multiple units can be used for higher output levels and true stereo bass. Video soundtracks not only sound spectacular through this subwoofer, but are also more accurate. Most important, the sound of the Force is so accurate that it will never be obnoxious or irritating -- it is meant to please for the long haul.

Manufacturer contact information:

Audio Concepts, Inc.
901 South Fourth Street
La Crosse, WI 54601
Phone: (608) 784-4570
Fax: (608) 784-6367

E-mail: sales@audioc.com
Website: www.audioc.com 

• Go Back