Not all home theaters are created equal. Said differently (and more accurately), not all custom installers and DIY builders bring the same experience/knowledge/performance standards to the job. Mistakes are made, some subtle, some egregious . The worst ones will be visible the moment you walk in the room, the lesser ones may require a trained eye to catch the error.
I'll probably touch on many of these in future posts, but in this space I want to discuss the one I encounter most frequently. Often, when I'm called in to do an ISF (Imaging Science Foundation) calibration on someone's system, I see it immediately.
But first some background.
The ISF, through its own research and looking at other studies, has determined an ordered list of things viewers care about when watching images on screen.
To jump to the bottom line, imagine this: 10 displays of all types—projector/screen, rear projectors, flat panels—encompassing all technologies—LCD, DLP, LCoS, OLED, Laser and Unaffordium—all in a dark room and all roughly calibrated, all showing the same clip(s). Now get a dozen people off the street who know nothing about video metrics and ask them which picture they like the best. 90% of them will pick the one with the highest contrast ratio.
Contrast ratio, you recall, is the quotient of the luminance at absolute black divided into the luminance at peak white, a.k.a., dynamic range. A large number will make the picture "pop," a low number will render the picture "washed out." Of all the video metrics, CR is clearly the most important (okay, the image has to be focused, too).
FYI, the numbers used to describe contrast ratio need to be post calibration, and they will bear little resemblance to the manufacturer's specs—due to said manufacturer's, uh, irrational exuberance!
Back to the big mistake, specific to projector/screen installations:
TOO MANY INSTALLERS OVER-SCREEN THE PROJECTOR!
For some context, here are three facts: People like big screens. People like to save money. Installers like to please clients.
The result is often a large screen with not enough light on it to produce a decent CR. At that point, everything else about the installation is lost. Once a projector is calibrated for black and white levels, a finite amount of light comes out the lens. The more you spread that fixed amount of light over more square inches of screen, the more the CR tanks. (Forget being "green," by the way— leave the lamp on High.)
Installers: Either reduce the size of the screen until you get 25 foot-lamberts (ft-L) or more off the screen, or convince the client to step-up to a projector with more light output. I like about 40 ft-L myself, but that's just me. Screens with as much as a 1.3 gain can help, but if you go that route be sure you know your screen materials. Another thing to consider is something called "Room CR." Any ambient light from any direction, such as red and green LEDs on component front panels that could splash on parts of the screen, will compromise the picture's contrast. Room CR sets the best black level you are going to get.
Mistakes will happen. But you should try hard to minimize CR errors and give an install the best shot at real success.