What Size Screen?...How Far Away?

"How big is the screen?"

"120-inches."

"Diagonal or wide?"

When I ask the last question at a trade show demonstration of a projector and screen setup, crickets often sing. If an answer is given before the chorus, it's nearly always, "diagonal." Diagonal is, after all, a bigger, more impressive number.

For years there was no confusion on this issue. When screens were 4:3 (remember those?) nobody talked in terms of the screen width. It was always diagonal. But when 4:3 started to mingle with 16:9, all bets were off.

But no sooner had 4:3 screens faded into TV Land than anamorphic projection popped up. It's all over the place at shows, now there's a new source of confusion. Suppose you just want to know how far you should sit from your screen for the best immersion and the fewest visible artifacts? Does this depend on both the size and shape of the screen?

It seems like everyone out there has an opinion on viewing distance, but the most useful answer may come from THX. As you might expect from a company that got its start by certifying multiplexes and movie palaces, and wants to see your home theater replicate commercial theaters as closely as possible, its answer comes from the theatrical cinema world. It recommends a subtended angle of 40-degrees from your seat to the left and right edge of the picture—and that's for a 1.85:1 presentation. For 2.35:1, it recommends even more: just over 50-degrees.

But THX also acknowledges that many videophiles will sacrifice a little envelopment for a brighter, sharper picture—which means a smaller screen. I'm in that group. A 40-degreee angle of view from a distance of, say, 12 feet will require a screen 105-inches wide or (for a 16:9 screen) about 10-feet diagonal. This, in turn, will demand something more than a budget or even midrange projector for a great picture, and will not be kind to standard definition sources. I use a setup with a field of view of approximately 30-degrees for both 2.35:1 and 16:9 material.

The THX recommendations can also be a bit impractical with a one-piece HDTV and its inevitably smaller screen. For example, a 40-degree field of view with a 60-inch (diagonal) screen would position the viewer about 6 feet away. Apart from the fact that you'll see every little flaw in the display or source (though maybe that's your thing), this is too close for many speakers (particularly multi-way floor- standers) to sound their best, not to mention gel together to produce a unified, coherent front soundstage. 30-degrees is better, at about 8 feet, though I suspect most viewers will be more comfortable at 10 feet. That's about the same distance Home Theater magazine used in its last face-off (with slightly smaller sets), and no one on the panel chose to use an optional, closer seating distance.

Whichever option you choose (and sometime in the next year I'm seriously considering switching a wider, 2.35:1 screen as a reference), a few formulas might be useful. The first two involve some approximation, but they will get you inside a very small ballpark.

Viewing distance, 40-degreee viewing angle = screen width x 1.36 Viewing distance, 30-degreee viewing angle = screen width x 1.86

Screen diagonal x 0.87 = screen width (16:9 screen) Screen diagonal x 0.49 = screen height (16:9 screen)

Screen diagonal x 0.92 = screen width (2.35:1 screen) Screen diagonal x 0.39 = screen height (2.35:1 screen)

You can confirm these formulas for yourself if you didn't sleep through trig class. There will be a pop quiz on Monday.

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COMMENTS
Tikkenator's picture

I have found this site very useful for determining appropriate screen size: http://myhometheater.homestead.com/viewingdistancecalculator.html

Joe Dokes's picture

I just bought a Samsung 61" DLP HL61A750 I think it is a very nice TV, cheap too, 1365. My wife was VERY fearful that the TV was going to be too large for our room 13' X 18', seating is between 10' and 12'. With High Def, the picture is spectacular, I hate nature shows but have watched EVERY episode of Discovery Channel's "Planet Earth" in high def, simply to look at the scenery. Truly spectacular, (Verizon Fios, plenty of bandwidth picture is VERY good few motion artifacts). All that being said, I really think that this is the largest TV practical for both TV and Home Theater. High Def looks great and you could probably sit a tad closer but not much. Standard Def looks noticeably soft though watchable. The key problem is Food Network, Diy Network, and HGTV, the morons who do the editing all were part of the MTV generation, fast cuts super close and fast zoom in and zoom outs. My wife literally gets motion sick. There are quite a few shows that are simply unwatchabl

Tom Norton's picture

Joe: I agree with you that a 60" set from 10-feet is a good combination. But as far as it being the largest practical size screenfor a home theater, there are a lot of folks with projectors who will disagree with you, even with good quality standard definition program material! For analog standard definition, however, a really big screen isn't the best choice. But apart from news and weather junkies, how many home theater fans are watching much SD analog programming these days.

Joe Dokes's picture

Tom, The Key point is home theater. My TV is dual use, and the quality of SD material even from Verizon Fios (which compresses the signal FAR less than Dish) is just too variable, some SD content looks okay others looks atrocious. DVD in general looks pretty good, though not nearly as good as HD. That being said, I am so sick of people (not you or others on this site) who say HD doesn't look that much better than SD. If I had a dedicated theater I'd probably go with a 6' scrren at 10' to 12' distance.

Allergy Resources's picture

These are all the information very useful.I also want to do it.Allergy Resources

argi's picture

so for 123 inc (16/9) how far is my seat

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mrh335's picture

Where is Part 4 of the bluray roundup? It's been three weeks and I feel a little jaded that we haven't seen Part 4 yet.

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