THX Certified

Illustration by Chris Gould; room photo by Tony Cordoza

See if this doesn't sound familiar: You don't just love movies, you love the whole moviegoing experience. When the time comes to check out a film, you drive miles out of your way to go to the best theater around-one with stadium seating, digital surround sound, and that awesome THX trailer that comes on before the movie.

Lately, you've been trying to figure out the best way to faithfully recreate that cinematic experience in your home. After checking out enough audio/video magazines and Web sites to arm yourself with the basics, you decide to visit your local A/V supercenter. But frankly, you're not impressed. A 36-inch TV coupled to a home-theater-in-a-box system isn't going to give you what you're looking for. You want a real home theater, with a big screen and mind-blowing audio.

Depressed, you leave-but on your way out of the store you notice a receiver with the familiar THX logo. Is it the same THX associated with movie theater sound? And exactly what do THX-certified components bring to the home theater party? Can they help you achieve your ambitious goals? As you've probably already guessed, the answer to the first question is yes. But to answer the other questions, it's best to start with a little history about THX and the movie company behind it.

In the Beginning

THX was born out of George Lucas's frustration. Watching the original Star Wars in a movie theater in 1977, he was disappointed with the sound æ what he heard didn't come close to recreating the experience he had had while mixing the film. He was also bothered because the soundtrack he'd worked so hard to perfect sounded different in every theater.

In 1980, Lucas asked Tomlinson Holman, then the technical director of Lucasfilm, to develop a set of criteria that would bring theater sound closer to what filmmakers intended moviegoers to hear, and in 1983 Lucas founded THX Ltd. (Although the name echoes the title of Lucas's first film, THX 1138, it actually derived from "Tom Holman's eXperiment.") In addition to establishing performance standards for theaters, the company announced a certification program for theaters that met those standards. By the time Return of the Jedi was released later that year, THX had certified its first two theaters. Today, there are more than 3,000 THX-certified theaters around the world, each of which is designed to provide the best possible picture and sound quality.

As VCRs grew in popularity and it became possible to get surround sound in your living room, the home began to rival the theater as a place to watch movies. In response, THX began working on performance standards for home A/V gear, and in 1990 it introduced the Home THX certification program. The goal was to set the stage for a home theater experience that was true to a film's original soundtrack. Today, several dozen companies are licensed to produce THX-certified components.

But simply buying good equipment doesn't guarantee a topnotch home theater. The gear must be properly installed and properly placed in a room that has been acoustically treated. That's why THX developed a certification program for dealer/ installers in 1991. Participants are trained at a hotel in Marin County, California, with day trips to Lucas's fabled Skywalker Ranch, including the Skywalker Sound facilities-where the mixing was done for such blockbusters as Titanic, Saving Private Ryan, and Jurassic Park as well as all five of the Star Wars films. To date, more than 4,000 installers have received THX certification.

The state-of-the-art Stag Theater on George Lucas's Skywalker Ranch is filled with THX-certified gear, including 29 speakers and ten 18-inch subwoofers. (© Lucasfilm Ltd., all rights reserved.)

A primary goal of the Home THX program is to preserve the filmmaker's vision. If you ask someone at THX why he doesn't recommend cranking your surround speakers to maximum volume, he'll tell you that's not how you were meant to hear the soundtrack. More to the point, he understands that your first experience with a movie is usually in the theater, and a home theater should replicate that experience as closely as possible.

THX also believes that you can't know what a good home system should sound like until you've experienced a state-of-the-art commercial theater, so installers-in-training also get to experience a screening at Skywalker's spectacular Stag Theater. The Stag's sound system is driven by a stunning 31,000 watts of power-far more than anyone would ever need at home, but it has to fill a 300-seat auditorium with sound. The system consists of five triamplified speakers arrayed across the front of the theater (far left, left, center, right, and far right), 24 biamplified surround speakers (eight each at the left, back, and right positions), and ten 18-inch subwoofers arrayed across the bottom of the screen. All of the equipment is THX-certified, of course.

Measuring Up

The most obvious difference between a commercial cinema and a home theater is the size of the room. That's why a movie that sounds fantastic at the cineplex can lose something when it's brought home if certain issues aren't addressed. Having determined that a typical home theater measures 16 feet wide, 21 feet long, and 9 feet high, THX has adopted those measurements for all of its certified sound-mixing rooms. Those dimensions also form the basis for the THX Ultra2 certification program for home equipment, which requires amplification and speakers optimized for spaces in excess of 3,000 cubic feet. The THX Select program is geared toward rooms in the 2,000 cubic foot range, or about 13 feet wide, 18 feet long, and 8 feet high.

While there's no question that you can put together a first-class home theater without THX-certified gear, going the THX route guarantees that all of the components æ even those from different brands æ perform to the same set of standards. THX hardware also contains special processing and refinements that help recreate the movie theater experience at home. Over the years, the list of components that THX certifies has grown to include receivers, amplifiers, preamp/processors, DVD players, video projection screens, speakers, subwoofers, equalizers, speaker wire and interconnect cables, speaker systems for multimedia PCs, and, most recently, car stereo systems. (For more on THX certification for home theater components, see Earning the Badge.)

These Walls Can Talk

Because a bad room equals bad sound, most of the THX installer training revolves around acoustics. Here are the major problems with room acoustics and how they can degrade a system's fidelity:

Room reflections As sound leaves a speaker, it doesn't simply travel straight to your ears. It bounces off the floor, the ceiling, the side and back walls, and even the wall behind the speaker. These reflections blur the sonic image and emphasize some frequencies while canceling others.

Slap echoes These are repeated reflections between parallel surfaces such as the side walls, the floor and ceiling, or the front and back walls. They produce a bright, zingy echo that degrades sound quality and imaging. Reverberation time As the sound leaves the speaker, it bounces, or reverberates, around the room until it "decays." If it takes too long to dissipate, more recently emitted sounds will become muddled. To preserve sound quality, installers modify the room's acoustics to achieve an optimal rate of decay.

Standing waves A direct result of a room's dimensions and the wavelengths of low-frequency sound waves, standing waves make the bass sound thin in one place and bloated in another. They can't be eliminated, but they can be tamed, usually by moving the subwoofer to another spot or adding another subwoofer. Rattles Fixtures, lights, windows, doors, furniture, and any other loose object can buzz or rattle. Usually caused by deep-bass notes, these effects are easy to hear and incredibly distracting.

Background noise Any sound you hear other than dead silence is background noise. Besides being distracting, noise can obliterate sonic details, like soft-spoken dialogue or subtle sound effects.

Taming Problem Rooms

While it may not be the most practical solution, one way to avoid many of these acoustical problems is to design a home theater from scratch. THX grads are given a computer program called a Room Mode Calculator, which is used to determine optimal dimensions that avoid acoustical problems like bass cancellation. A qualified installer can advise your builder on wall construction and soundproofing techniques to ensure that the room will be quiet inside and out. For example, a heating/ cooling system that's not properly situated and insulated can produce unacceptably high noise levels in a space that should be as quiet as possible. Even if you can't start from scratch, a qualified installer will use test gear to identify acoustical problems and then correct those problems with appropriate treatments and equalization.

Room treatments come in two basic flavors: absorptive and diffusive. Absorptive materials, which soak up sounds (mainly in the upper frequencies), include drapery, fiberglass, and dense foam. Diffusive materials, which break up and scatter sounds, include furniture, bookcases, and specially designed panels. Both kinds of treatment can be expensive and hard to employ, but THX provides schematics showing how various treatments on the front, back, and side walls of a room can be used to overcome acoustical problems.

As noted earlier, standing waves can be a big problem. Fortunately, the THX Room Mode Calculator can also be used to plot out where standing waves will appear so the installer can take measures to subdue them, often by rearranging the seating or moving the subwoofer. In some cases, multiple subwoofers or a custom-made "diaphragmatic absorber" will be used to even out a room's bass.

After the room treatments have been completed, equalization is used to smooth out any remaining bumps and dips in the system's response curve. The installer will take test-signal readings at various locations and plot them on a spectrum analyzer. Then he'll use a one-third-octave equalizer to tweak the response of the front and surround speakers and a one-sixth-octave equalizer to get the bass just right.

In addition to offering a wealth of information on proper home theater setup, THX-certified installers also have access to the THX consultation services, which can be helpful in tackling difficult acoustical problems or getting the best results in an unusual space.

Audio's Better-Looking Half

A home theater isn't a theater without stunning video. And what kind of video display you choose will have a lot to do with how your room is laid out. The first thing you need to do is figure out how big a screen the room can accommodate. A THX installer-or any professional installer, for that matter-will not only help you decide on the right size screen, but also assist in determining what arrangement will provide the best possible viewing experience for everyone in the room.

While THX-certified installers are trained in basic video adjustments like color, tint, and brightness-and calibration using a test-pattern disc (see page 119) can get you 90% of the way there-a truly first-class theater requires the kind of thorough video calibration that only a technician trained by the Imaging Science Foundation and using proper test instruments can provide. (For more on the ISF, see TV Tweaks: House Calls.) But it's likely that any installer who's had THX training will be ISF-certified as well. The next time you're in a store and you see the words, "THX Certified Dealer/Installer," ask the salesman to fire up the "Wow!" demo. If this clip doesn't get you excited about the prospect of having a killer home theater, you might want to check your pulse.

John Sciacca, lead system designer at Custom Theater & Audio in Murrells Inlet, SC, has attended the Home THX training class. For a list of THX-certified installers, go to the dealer locator at