Get a load of those feet. Someone slipped a set of solid brass isolation cones on Pinnacle's AC Sub 100, a working-class $350 subwoofer dressed humbly in black vinyl. So what's with the magic slippers? Another Cinderella story perhaps? Or is it merely a Mr. Blackwell - caliber fashion faux pas, like matching Prada with Wrangler? Well, the AC Sub 100 isn't a thing of beauty, but you can take it to the ball-or put it in your entry-level home theater-without embarrassment. This 13-inch cube can dance a bit. The AC Sub 100 resides at the low end of Pinnacle's subwoofer line, and its feet are hand-me-downs from the companies more-exotic designs. They're standard equipment on, among others, Pinnacle's $1,200 Digital Sub 600. Is there another manufacturer that fits such fancy footwear on its nickel-and-dime subwoofers?
Unlike so many subwoofers in the ultra low-budget division, the AC Sub 100 also has a 10-in driver. The heavyweight fibercone woofer allows the AC Sub 100 to dip down to a rated 33 Hertz, a region most budget subs with standard 8-inch drivers have never seen.
Now for the more mundane. This bottom-vented sub with a fourth-order low-pass filter is powered by a 100-Watt, class A/B amplifier designed by Pinnacle. It weights only 22 pounds which is frightening lightweight for a sub with a 10-in driver. The cabinet is made of half-inch medium density fiberboard. Knock on the cabinet, and it sounds as if no one's home, the hollow tone indicating a minimum of internal damping. In most applications, that makes it difficult to prevent vibration and the resulting dirty-as-a-compost-pile sound. However, the AC Sub 100's vented design relieves internal pressure to help eliminate vibration. Pinnacle has also incorporated an anti-clipping circuit - also known as "soft clipping" - into the amplifier that prevents it from being overdriven at dynamic peaks, where it is susceptible to increased distortion. Pinnacle chose the 10-inch driver, in part, because it requires less movement and produces less distortion to reach the same volume levels as an 8-inch driver.
And don't forget those brass cones. They reduce vibration interacting with the floor, which could otherwise turn the sound into a muddied mess. They also provide a critical service, elevating the sub sufficiently to give the bottom vent the necessary room to exhale. Isolation cones have long been recognized as possessing magical powers, a tweaker's fetish, in reducing vibration and enhancing the clarity of all things electronic. The cheap plastic sphere included with the average budget sub just don't do the trick. I recall one manufacturer, with an otherwise excellent subwoofer costing about $100 more than the AC Sub 100, that didn't even leave holes for the plastic feet. It packed the feet and metal screws in a bag with drilling instructions for the holes. That experience made the discovery of Pinnacle's brass cones even more shocking.
There were more surprises to come. The AC Sub 100 I received not only lacked basic speaker-level inputs but also a variable crossover. Wait a minute. Beautiful brass isolation cones and no speaker-level inputs or variable crossover? What was this, Candid Camera? Turns out the particular sub I received was an earlier production model. Pinnacle has since added a variable low-pass filter crossover (50 to 150 Hz) and an LED that shines red when the sub is powered on, but there are still no speaker-level inputs on this sub.
The AC Sub 100 does have a phase switch, a level control, and a single line-level input: however it lacks an auto or manual on/off switch. So, if you're using the sub with a receiver that has no switched AC connections, like the Outlaw, you'll either have to shut it down by unplugging it or simply leave it on around the clock.
Even so, the AC Sub 100, paired in my system with an assortment of PSB Alpha speakers and the Outlaw receiver, makes a superb entry-level setup for less then $1,600. The 10-inch driver needed an extended break-in, so I left the Pinnacle's crossover at its highest setting, shut down all the other speakers, and ran MTV through the sub for three days. Then, with the sub about 2 feet from the far corner of the room, I calibrated the system using test signals from the Avia Guide to Home Theater. When I checked the AC Sub 100 at about 40 Hz (where most budget subs bottom out) it measured a rockin' 98 decibels without overextending itself. That 40 Hz sock proved to be the sub's signature.
A series of warble-tone tracks from Stereophile's Test CD 3 revealed an 8 dB bump over the reference signal at 40 Hz, as measured by a sound-level meter. This could be attributable to my room, or it could be the sub's design. Either way, this is where most budget subs hold their last stand. That generous outputs at 40 Hz although clearly in midbass territory, rendered a pleasing, fully rounded low-level affect. The AC Sub 100 dropped off rapidly at 32 Hz, even though it kept fighting.
The AC Sub 100 passed all special - effects tests: trains (The Fugitive), planes (Independence Day) and automobiles (Tomorrow Never Dies). But it could not replicate the true low bass that presses against the chest. It simply could not do justice, for example, to "The T-Rex Intrudes" chapter of "The Lost World". It didn't exactly blow me off the couch like some bigger drivers in bigger cabinets. Of course, I didn't expect it to. Fortunately, it didn't have that intrusive, one-note effect of so many other budget models. Now that was a surprise.
The AC Sub 100 was more nimble, more understated. It was the first budget sub I didn't have to either turn down or turn off when switching to music. It gave a more-realistic reading of bass transients than the others, if a little richer and slightly more sluggish than more-expensive competitors. I subjected it to material ranging form "Muy Divertido" (Very Entertaining) by Marc Ribot Y Los Cubanos Postizos, an Afro-Cuban project by the New York guitarist, to rockabilly roadhouse legend Sleepy LaBeef's "Strange Things Happening". Labeef's basso profundo makes him the closest thing to a human subwoofer test tone.
The AC Sub 100 also steered easily through some high resolution audio discs after I replaced the Outlaw receiver and the Onkyo DV-S535 DVD player with the Marantz SR7000, which has a 96-kHz digital to analog converter, and the Pioneer DV-C503 multichanger, which outputs a 96 kHz PCM signal. With this setup, I could play some of Classic Records' digital audio discs, which achieve 24/96 resolution under the DVD-video format, developed as a delicious preview of high resolution audio while the DVD-audio format was being sorted out. The sub took "Somethin' Else", the Miles Davis session released under Cannonball Adderly's name without flinching. On "One For Daddy-O", in particular, Sam Jones' bass received the additional attention it deserved while retaining a sense of proportion with the other instrumentation.
In any setting, the AC Sub 100 filled in the midbass without diving too far, or to clumsily, into the lower regions. It never made a fool of itself, honking or squawking unnecessarily. It was a team player, always. To get this sort of versatility in a sub that lists for $350 is a rarity in home theater's budget division. If you've put together a system and lack only a subwoofer, it's time to jump in. With the AC Sub 100, that's feet first.
By Kevin Hunt • Home Theater