This year a group of my old friends decided to set up a demonstration at CEDIA EXPO to show the importance of engineering, acoustics, and calibration. We took two identical rooms in a hotel and equipped them with identical A/V systems. One was set up in a traditional way, matching the characteristics of a typical home theater installation. The other room was engineered, acoustically treated, and equipped with room-tailoring equalization. Attention was paid to a whole host of other little details to optimize the rooms performance. Visitors to the demo first got to hear a few clips of multi-channel music and film in the traditional room, and then they quickly shuffled into the engineered room to experience its effect on the same program material.
The difference in quality was staggering. Even after all this time, I had never had a chance to hear the A/B comparison so directly. The traditional room sounded just fine; most of our customers would be perfectly happy with it. But the engineered room was superior in many ways: sharper soundstage, clearer dialog, better articulation, tighter bass, and even cleaner picture quality.
The recipe for improvement was pretty straightforward. It called for some preparation time, some added ingredients, and some special care in mixing it all together. Follow this recipe and you can get that extra spice out of your A/V installations:
Analyze the rooms dimensions to check for any strong bass resonances. If you find some, be prepared to incorporate bass traps.
Treat the room with absorption, diffusion, and low-frequency absorption. Use just enough to bring the reflection decay time down to about 0.3 seconds. Usually that takes 25 percent coverage of the wall surface with absorption and 25 percent with diffusion. Make sure that the first reflection points of the front speakers are all treated. The absorption and diffusion should be broadband so that they dont just suck all the high-frequency energy out of the room. Use at least three-inch-thick absorption and four-inch-deep diffusion.
Place the seats so that they are neither in peaks or dips of bass resonances in the room. Make sure that the back row(s) are raised up so that everyone has good sightlines and soundlines.
Use multiple subwoofers distributed throughout the room to reduce resonances. Hook them up in mono and if possible, adjust their position for smoothest frequency response by using a spectrum analyzer.
Place the left/right speakers to form a 45-degree angle to the seating area, and keep them away from corners, floors, and walls. Place the center speaker behind an acoustically transparent screen. That gives you a picture-to-sound match and gets the Center height to match the left/right speakers. Aim the front speakers toward the center of the seating area.
Choose speakers with directivity that matches the room acoustical character. In a large, live room, use speakers with a focused radiation pattern. In smaller, well-damped rooms, use speakers with broader dispersion. How do you know the speaker directivity? Try asking the speaker designer. If they dont know, they didnt do their homework all the way.
Use a room-tailoring equalizer. This device connected between the A/V controller and the amplifiers is a crucial part in tweaking the system to the room. You cant forget it! You will, of course, need to own a good spectrum analyzer and know how to use it so that you can tune out the room issues.
Keep the projector quiet by putting it in a hush box. Any noise levels above 25dB (NC method) in the room will cut down the soundtracks 100dB dynamic range.
Use dark colors on the walls, floor, and ceiling. A room with light colors will reflect light from the screen back onto the screen, washing out the contrast. Theres no point in specifying a high contrast display device if its going to be limited by the room.
Choose a screen size thats not too large and not too small. Too large and you will be constantly distracted by image softness, motion artifacts, and excessive eye motion. Too small and you just dont get drawn into the movie. A target for viewers watching mainly DVD is a screen width 0.55 times the seated distance. Hi-def users can push up to 0.71 times the seating distance.
Spend time in final system verification, configuration, and tuning to eek every ounce of performance out of the room.
My group of friends, also known as the Acoustics Guild, followed this recipe in setting up the engineered room. It was nothing super tricky, just a good way to cook up a great-sounding and great-looking theater.
You can learn about all these recipe points by following the courses offered at CEDIA events, as well as by going to ISF, HAA, and THX seminars. CEDIA University and Certification programs are also a good way to show your customers that you paid your dues in learning how to cook up a tasty home theater for them.
Anthony Grimani is president of Performance Media Industries in Fairfax, California.
Chase Walton contributed to this article.