Originally Posted by Glen Graham
Check my signature for photos. "Rules of thumb" are too narrow, and suck; everybody should choose their own desire.
People who argue this (and some people who use rules of thumb) don't take them for what they are, guidelines, starting points, sanity checks. As such they are useful.
If someone comes in here and says "I want to set up a home theater to watch movies, my room is x by y by z and I'll sit L away, help." Telling them "Do whatever you want" helps no one. Rules of thumb are good places to start.
Say that same person said they were going to sit 15' from the front wall and was planning on getting a 32" TV because it's way bigger than the 19" CRT they had before. Well we all know that's crazy, that's way too small, but how do we know that, how do we guide a new person to a realistic solution? Well we compare it to some rules of thumb or industry guidelines.
Common guidance is seating for a theater should be between 2 and 4 picture heights and with a brightness around 16ftL, a 32" TV at that distance is more like 12 picture heights. A more realistic size is between 3.5 and 7', (42 to 84" high). From that we can derive that 84 is probably pushing it size wise (potentially hard to fit in a room and expensive to light) so the user might want to consider moving their seating closer (if they like a big picture). Or maybe they'll need to look into "big iron" projectors or high gain screens to light it all.
But now we have a good starting point. It's helped avoid someone going off into never never land with a system that can't possibly work optimally, like a tiny screen they'll regret later or getting way too big of a screen for the projector they choose to light it with, and being unhappy with the dim picture.
From which (I absolutely agree) the user/OP/new person can draw their own final conclusions about exactly how close they want to sit and how large and how bright they want their solution to be.
In the end it's all about the user being happy with what they have, regardless of if that solution falls within norms or guidelines, but that doesn't mean norms/guidelines/standards are worthless.
I want to address this:
Before I built my theater, we projected the picture (from a stepladder) onto the blank wall, experimenting with different sizes and placements. After a few weeks, we measured, and realized we **LIKED** 132" back from a 133" screen (18" off the ground).
This is a great idea, but it requires that you have some idea of how big and how bright you want to be. How would you have felt if you'd bought a little 200 lumen LED Pico projector, because they're cheap, and LED, and everybody raves about them, only to find out you'd only have about 3ftL of brightness with that setup?
Now obviously that didn't happen, you had a frame of reference to know that a relatively bright HT projector could light that. But if you don't have that frame of reference, that's where rules of thumb come in handy to have a sanity check before hand to avoid planning something that's so far outside of the norm that it's unlikely to work.