As you know if you've seen the latest remake of King Kong, brontosauruses invented bass. In the millions of years hence, it has caused nothing but problems.

Don't blame the lumbering beasts. They had no idea how difficult it would be for us humans to reproduce their thundering footsteps in our living rooms. The physics of bass are well-understood—a little bit of math can tell us the deepest bass note a subwoofer can reproduce, and which bass notes will boom out in a room. But we have had a difficult time turning that knowledge into accurate reproduction in a room, especially when it's for an audience of five or six people, not just one. Unless you frequent Krispy Kreme, you probably don't know what the steps of giant, hulking creatures really sound like.

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JBL's HTPS400, a THX-certified subwoofer with a 12-inch driver, formed the basis of the JBL test system. Four were used, but according to JBL, good results can be achieved with only two. (Click image to enlarge)

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The last few years have seen an explosion of interest in bettering bass, largely because digital signal processing (DSP) chips now have the horsepower to fix many bass problems. But DSP can cause problems, too. Bass response usually changes dramatically as you move around a room. Certain notes boom out, others practically disappear—even if you move just three feet over. Therefore, if you use an equalizer to correct the sound for one seat, you might make the sound in the next seat worse

Four on the Floor
The company that has devoted the most research to this subject is Harman International, parent company of JBL, Infinity, Harman/Kardon, and many other audio brands. The company has recently been touting the superiority of using more than one subwoofer. Most audio professionals are aware that using more than one subwoofer can help smooth the bass response in a room, but few really know where to place that second (or third, or fourth) subwoofer. The company's ultimate recommendation for the best bass performance in a typical, rectangular room is to place one subwoofer in each corner. Its presentation sounds good on paper—but so did Troy. Hearing my skepticism, Harman's scientists offered to prove their theory by setting up four subwoofers in my listening room.

Harman manager of objective evaluation Allan Devantier showed up with a quartet of compact HTPS400 subwoofers, each with a 12-inch driver and a 400-watt internal amplifier. He placed one in each corner of my 15-by-28-foot listening room, then connected each sub to a DBX DriveRack 260 digital audio processor. The DriveRack 260 is a sophisticated, six-channel digital processor that performs equalization, delay, and volume control. (We used my Genelec HT205 speakers to provide the midrange and treble.) Devantier then flipped open a laptop and used Harman-developed software on the laptop with special microphones to take sound measurements of my room from each of several seating positions.

Devantier's goal was to see how bass was affected by my room's shape and construction, and the position of my seating. "The Harman software suggests 10 solutions for the equalization, delay, and gain [volume] of each subwoofer," he explained. "It gives a predicted response curve for each solution. We pick the one we think is nicest, and set the DriveRack 260 accordingly."

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JBL engineers used the DBX DriveRack 260 as the equalizer for the four subwoofers in the test system, but a JBL-branded, purpose-built subwoofer EQ is slated for introduction in early 2007. (Click image to enlarge)

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The results were instantly impressive. I started by playing music CDs with bass lines that covered a wide range, to make sure no particular bass notes stuck out or vanished. In my main, front-and-center listening chair, the response was practically perfect. But I expected that. As I moved to different chairs, though, the bass response changed only a little. Even in the worst chair in my room—the one to the left of my front-and-center chair—the variation in level from one bass note to another was minor. To my surprise, the bass had plenty of "punch" and definition, which is usually not the case when a subwoofer is placed in the corner.

"The biggest improvement you get is when you go from one to two subwoofers," Devantier said. "If you go with two subs, you can place them at the midpoints of opposing walls, or in the two front corners. Four is better, though. Placing them in the four corners gives the best compromise of smoothness and output."

Another benefit is that the four subwoofers can be relatively small. Four small subs can do more work than one large one—four 10-inch woofers, for example, have about 24 percent more surface area than a single 18-inch woofer. And Harman's methods ensure that the subwoofers don't waste energy by fighting against each other.

Chris Neumann, director of sales for JBL's Systems Integration Group, says that late this year, JBL will offer a multi-subwoofer equalizer designed for use by installers. Called the BassQ, it works for as many as four subs, and has inputs for four measurement microphones. This product, which will retail for about $2,000, promises everyone the chance to achieve what I heard in my listening room. A more sophisticated line of Synthesis Digital Equalizer Crossovers—which cover the entire range of sound, not just the bass—is planned for 2007.

Solo Performance
Another method for subwoofer optimization is Velodyne's Digital Drive system, which is incorporated in its DD-series subwoofers and in the SMS-1 stand-alone audio processor. The Digital Drive system provides a measurement microphone and a sophisticated subwoofer equalizer you control through an interface that appears on your TV screen. It can be set manually, or it can make the adjustments automatically. We tested the DD-15 subwoofer a couple of years ago and fell in love with it. The SMS-1 promises a similar level of excellence from non-DD—and even non-Velodyne—subwoofers.

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The SMS-1 equalizer brings Velodyne's Digital Drive technology to any subwoofer. It can be used in automatic or manual modes. (Click image to enlarge)

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Unlike the Harman system, the Digital Drive system is intended primarily to optimize the sound in one seat, although if you switch to manual mode and make adjustments in multiple seats, you can loosely average out the responses.

The SMS-1 coaxed my James Loudspeakers' EMB-1000 subwoofer to even greater performance levels. The sub's upper bass notes were already well-defined; the SMS-1 gave them more intensity and drive. My room's most significant bass problem—a bump in the response around 40 hertz, which is about the same frequency as the lowest note on a standard bass guitar—nearly disappeared. One thing the SMS-1 does that other bass optimization systems don't is that it can give you both by-the-book bass, and bass optimized for your taste. It has presets for different types of music and movies, any of which can be fine-tuned as you like.

According to both my ear and the measurements I took later, using the SMS-1 with a single subwoofer leaves you with a great deal of variation in the sound when you move from seat to seat. However, adding more subwoofers and more SMS-1s can smooth these problems out. Velodyne recommends not adjusting the equalizer for the primary subwoofer, and using the automatic features of the other SMS-1/subwoofer combos so they adjust themselves to supplement the primary sub.

Other Voices
We have also experienced two other interesting approaches to bass optimization. One comes from subwoofer maker REL, and it was profiled by contributor Steve Guttenberg in his July/August 2005 "High-End Audio" column. It involves connecting three subwoofers. One is driven by the subwoofer output of a surround processor or A/V receiver. The second is connected to the surround speakers and is placed in the rear of the room. The third is connected to the center speaker and is placed near that speaker. (The company says the method works with any brand of subwoofer, but that its own are designed to make setting up this three-sub system easier.) Guttenberg reported excellent results, noting in particular that using three RELs resulted in a heightened sense of ambience and improved dynamics. Of course, this system's result will vary with the program material—for example, you get no benefit when you play stereo music because the center and surround channels are inactive. And there's no guarantee that the positions REL recommends will be optimum for your room. But it is simple to set up and requires little adjustment.

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Audyssey Labs' Sound Equalizer (shown in front and back views) automatically corrects for audio reproduction errors caused by room acoustics. It's designed to have a positive effect for all seats in a room, not just one. (Click image to enlarge)

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Another promising approach comes from Audyssey Labs, whose MultEQ automatic optimization technology is already incorporated in many audio/video receivers. The company's new Sound Equalizer connects between any surround processor and amplifier. Your installer calibrates the Sound Equalizer automatically, using a laptop and four measurement microphones. In a recent demonstration at the University of Southern California's Immersive Audio Laboratory, the Sound Equalizer impressed us with the consistency of bass quality as we moved from seat to seat. One limitation is that although it can be connected to multiple subwoofers, it applies the same corrective equalization to all, so it cannot optimize multiple-sub systems as effectively as Harman's technology can.

All of these systems debut this year, so it is too soon to tell which will succeed. But all of them will surely be better than what most people have now—one or two subwoofers, neither one placed optimally, and both fighting futilely against their surroundings. Home theater enthusiasts deserve better bass, and now they can get it.