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Home Theater Yoga Moves

Specifying a System that Accommodates All Video Formats
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So a client comes to you and says, “I love movies from a lot of different eras, but there are so many different picture and sound formats! Design me a home theater that will present all of them as close to the original experience as possible.” That’s a pretty tall order, but it can be done with a little forethought and ingenuity. Let’s do a quick rundown of things you’ll need to do for the picture, sound, and room aspects of such a large-scale project.

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Sizing Up the Picture

For the picture, you’ll want to start with Ultra HD projection and a four-way masking, acoustically transparent screen, optical pathway and sightline study, room lighting and color control, and display calibration. Over the years, the size and aspect ratio of movie pictures has changed dramatically. While a 2:1 screen with four-way masking is adequate when a 2.35 Blu-ray at 40-50 degrees viewing angle is the largest image, for this project you’ll need to go ahead and bust the edges of that 2:1 screen out to 2.3:1. You’ll need the wings to create a 2.76 image wider and larger than 2.35. That’s a legitimate 12- to 15-foot wide screen with a 60- to 70-degree viewing angle. It will take at least 4,000 calibrated lumens to hit 16 to 20fL on such a giant screen. You’ll need masking stops for a dizzying variety of ratios: 2.76, 2.55, 2.39, 2.35, 2.20, 2.0, 1.85, 1.78, 1.66, and 1.33 at least and probably a second smaller set for low-res sources.

Expanding the Sound

For the sound, let’s go with immersive audio, a sound system that covers the seats evenly, four subwoofers in corners, manual DSP EQ for each speaker, and full commissioning and tuning. The large-format cinemas that screened the epics of yesteryear had equally impressive sound, anchored by five screen channels to fill the gaps between left, right, and center. Ultra HD finally supports a picture big enough to warrant five screen channels, and Dolby Atmos supplies the audio format to support it.

But big sound is more than just extra channels behind the screen. Full implementation of immersive audio requires extra pairs of surround and ceiling speakers–up to 34 channels for Dolby Atmos. Plan at least two pairs of side speakers, two wide, and six top speakers, and two to four back speakers. That may seem like a daunting number of speakers, but they don’t have to be that large if you implement a subwoofer crossover at 120Hz.

Subwoofers must produce reference-level SPL of 115-120dB, so consider four 18-inch woofers with 1000W behind them or multiple 12-inch units. Don’t risk under-powering the other channels, either. The newer crop of switching-supply amplifiers offers huge power reserves in small packages with very little thermal output.

Finally, time-alignment, EQ, and additional tuning of the system should be handled by a skilled craftsman piloting a digital processor, not an automated process.

Environmentally Friendly

For the room, provide complete acoustic design, sound isolation, noise control, interior acoustic treatment, and seating optimization. Go with a minimum of 6- and preferably 12-inch deep acoustical treatments. That kind of depth is necessary for full bandwidth acoustic control. A frequently overlooked area is the floor bounce in front of the screen. Solve this by constructing an absorptive pit in the floor.

Take background noise seriously; RC15-20 is the target for a nice room. Because all of the extra audio channels pump hiss into the room, watch out for speakers with extremely high sensitivity. HVAC noise will also be problematic. Run calculations beforehand and be prepared to source extremely low noise components and electronics.

Analyze the ratio of direct to reflected sound from the speakers, and the direct vs. sound power frequency response. Essentially, you are striving to create a pleasing balance of direct sound from the speaker vs. reflected sound from the room so that the speaker sits inside a nice acoustic space. A further step is to analyze how the off-axis frequency response of each speaker differs from the axial and to custom tailor the acoustic treatment at reflection points to even out any raggedness in the off-axis response.

Finally, adopt a mantra similar to the Hippocratic Oath when dealing with décor: Do no harm to the sound or picture. Some focused lighting on the seats and architectural elements is a great enhancement during the show, but keep it low and entirely off the screen. Ideally, surfaces should be dark neutral gray or taupe. It can be ugly, but colored and themed lighting can work wonders to create ambiance. Many elements like wood columns that reflect sound and light can be replaced by acoustically transparent material with absorption and diffusion behind them. In practically every circumstance, there is a creative way to achieve the desired visual look while maintaining performance criteria.

Chase Walton contributed to this column.

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