Ask S&V

Q I’ve seen a couple of instances in Sound & Vision magazine of installations with a flat-panel TV for normal viewing and a projector and large screen for special viewings. If the screen comes down in front of the flat panel, how do you arrange room seating to accommodate both screen sizes? A 60-inch flat panel and a 100-inch projection screen for instance?—W. Ladd Romans, Jr. / via e-mail

A Not easily. For a dual-screen installation such as the one you describe, the flat-panel TV is used for casual viewing and situations where you don’t want to fuss with dimming lights and firing up a projector. And while you don’t want to be too far away from your flat screen when watching the news, the focus of the installation should be on optimizing seating for movie viewing on the bigger screen.

THX, SMPTE, and other sources provide guidelines that you can look to when planning optimum seating distance for a given screen size. Both THX and SMPTE take into account field of view, or the level of immersion you’ll get at a fixed distance from the screen. THX recommends a 40-degree field of view for a projection setup, and you can figure out the correct THX seating distance in inches for a given 16:9 aspect screen using the following formula:

Screen Diagonal (inches) / 0.84 = viewing distance (inches)

With a 100-inch screen, for example, THX guidelines would place you 9.9 feet away. For SMPTE, the ideal field of view is 30 degrees, which will place you a bit further away. To get the recommended seating distance in inches for a SMPTE-approved setup, you use this formula:

Screen Diagonal (inches) / 0.6 = viewing distance (inches)

While the THX and SMPTE formulas both have merit, some may find that they position you a bit too close to the screen. For those folks, a more relaxed, realistic rule is to sit somewhere between 1.5x and 2x the diagonal screen measurement. Following this guideline, the optimum seating distance for a 1080p-resolution display on a 100-inch screen would fall somewhere between 12.5 and 16.5 feet. (When you step up to 4K projection, the pixels are finer, of course, so you can sit much closer to the screen without seeing any distracting pixel structure in the image.)