The Miller Channel
By Kevin Miller
Thinking about taking the plunge into a two-piece front-projection home theater? Don't make a move until you read this article.
If you are looking to create a truly cinematic experience in your home, front projection is the only way to go. The sheer visual impact of watching movies on a huge screen, displayed by a separate projector, simply can't be matched by any other technology, either in image size or picture quality. Making the move from a rear-projection television (RPTV) or direct-view set to a full-blown front-projection home theater is a big step, but one that can be vastly rewarding.
In this article, we'll look at how to plan and set up a two-piece front-projection home-theater system, including selecting a screen size and material, finding the optimum seating distance, managing ambient light, and choosing the video-display technology.
Matching the System to Your Room: Screen Size and Viewing Distance
Just as the room in which an audio system is placed affects sound quality, the space where you set up your front-projection system will affect the picture quality. Your room's characteristics may also influence the maximum screen size, seating distance, and even the projection technology you choose.
A crucial factor in achieving a satisfying picture is screen size. Choose a screen that's too small and you won't enjoy as great a visual impact. Pick a screen that's too large for your projector and picture quality will suffer-the image may lack the bright, smooth, film-like image we strive to recreate in our home theater. (See Jonathan Valin's discussion of the importance of picture size in his "Dream Theater" piece in Issue 37.)
The two most important factors in determining the best screen size for you are the front-projection technology (CRT, LCD, DLP, D-ILA; see Peter Putman's feature article this issue for a full explanation) and viewing distance. We'll first consider the projection technology. CRT projectors are the most finicky about screen size because they output the least amount of light of all the projector types. As that limited light output is spread out over a larger area, the picture becomes dimmer. We can crank up the projector's output to compensate (up to a point), but resolution decreases (image quality suffers) and the CRT life is shortened. It's a big mistake to mate a CRT projector with a too-large screen.
CRT projectors come in three flavors: those with 7", 8", and 9" CRTs. Larger CRTs generally have greater resolution and higher light output, which means a 9" CRT projector can be used with a slightly larger screen (all other factors being equal). Specifically, 7" and 8" machines will produce the best picture when mated with a screen no larger than 72" wide and a 16:9 aspect ratio. Projectors employing 9" CRTs will yield the best results with screens up to 84" wide and a 16:9 aspect ratio.
Notice that I specified screen size in width and aspect ratio rather than diagonal measurement. This is a more precise method of describing a screen, and one that you'll use when ordering yours.
If you choose an LCD projector-these, unlike CRTs, use a fixed-pixel array-you may be tempted to use a larger screen because LCD projectors have a much higher light output than CRT projectors. For example, while an expensive CRT projector may have a light output of 260 ANSI lumens, a budget LCD projector may produce 1000 (400 or 500) ANSI lumens. But before you order that 12' wide screen for your LCD projector, keep in mind that the larger the picture size, the greater the visibility of the individual picture elements (pixels) that make up the image. LCD projectors exhibit a phenomenon called the "screen door effect" that superimposes a black grid over the picture, as if there were a screen door in front of it. These black lines are formed by the spaces between pixels in the LCD panels. The larger you blow up the image, the more visible the pixel structure.
DLP and D-ILA are also fixed-pixel projectors, but are a different story altogether. With these types of displays, larger screen sizes actually help produce better images, yielding better black levels-the color black is deeper and less gray, giving the picture greater contrast with better resolution of detail in dark areas. DLP and D-ILA projectors exhibit much less of the "screen door effect" than transmissive LCD units, because the space between the pixels (called "fill factor") is much smaller. Because the light output of DLP and D-ILA projectors is so high, you may even get eye fatigue with smaller screen sizes and prolonged viewing.
Now for some numbers. Single-chip DLP projectors (the kind you'll find in consumers' homes) range in brightness from about 700 ANSI lumens for 800x600 resolution projectors to about 1000 ANSI lumens for higher resolution 1024x768 projectors. For these single-chip DLP projectors I recommend screen sizes ranging from 84" to 96" wide in a 16:9 widescreen aspect ratio. Behemoth three-chip DLP projectors, used primarily for electronic cinema applications, are also available, but they are extremely expensive, and best suited for huge screen sizes of 15' to 30' wide or larger.
Today's three-panel D-ILA projectors are about twice as bright (from 1500 to 2000 ANSI lumens) as most single-chip DLP units, and optimum results require even larger screen sizes. Choose a screen ranging from about 96" to 132" (8' to 11') wide. You'll get better black level performance from a large screen, but also keep in mind that 1500 to 2000 ANSI-lumen-capable projectors will hurt your eyes on smaller screen sizes even when the contrast level is set to minimum.
The other crucial factor in determining the optimum screen size for a front-projection home theater is the distance from the surface of the screen to the primary seating position in the theater. Assuming your system includes a video processor (line doubling, tripling, or scaling) for NTSC sources like DVD, a good rule of thumb is to be three to four times the picture height away from the surface of the screen at the primary seating position. For example, with a 72" wide screen, which has a height of 40.5" (16:9 aspect ratio, of course), the ideal seating distance would be between 121.5" (10.1') and 162" (13.5'). The idea is to sit as close as possible so that the screen subtends as large a field of view as possible, yet not so near that you can see the picture structure, whether that structure is made up of scan lines on a CRT-based projector, micromirrors on a DLP unit, or pixels on an LCD or D-ILA projector.
As you can see, the room in which you'll install your front-projection system influences every other major decision. Start by determining the seating distance that works in your room; this figure will not only determine the optimum screen size, but may play a role in determining the projector technology you'll buy.
The screen material you select for your front-projection system is more important than you might realize. Screen surface materials vary widely, and what is optimum for a CRT projector is not necessarily optimum for fixed-pixel display technologies.
Screens are categorized by their gain, a figure that expresses how much light they reflect to the viewing position. Most high-performance home-theater screens have a gain of 1.3; screens used for corporate visual presentations may have a gain of 4. (See sidebar)
A low-gain (less than 1.5) screen is best for CRT-based projectors because it produces the best white-field uniformity (evenness of color on a white field from left to right across the screen), and will not exhibit blooming or hot-spotting (areas of the picture that are brighter than others) in the center of the screen.
The Imaging Science Foundation (ISF, www.imagingscience.com) has tested and approved screen materials from Stewart Filmscreen and Da-lite. Stewart's StudioTek 130 is a 1.3-gain material that is perfect for CRT-based front projectors. Da-lite's ISF-approved material for CRT projectors is called Cinemavision 1.3, and has the same low gain (1.3) as Stewart's StudioTek 130.
The recent explosion in popularity of fixed-pixel projectors (primarily DLP-based units) has caused screen manufacturers to develop materials optimized for the very high light outputs of these projectors. Stewart's new Grayhawk material actually looks gray rather than white, and produces much deeper blacks than StudioTek 130. Similarly, Da-lite's High Contrast Da-mat has a very low gain, again conferring better black-level performance (higher contrast and more visual "snap") and better white-field uniformity. These extremely low-gain materials work because fixed-pixel projectors have about five times the light output of CRT projectors-they have light output to spare.
Before you choose Grayhawk or High Contrast Da-mat for your DLP or LCD projector, however, ask yourself if you'll ever switch to a CRT projector in the future. If there's a chance you'll upgrade to CRT, go with the standard 1.3-gain screen; the super-low gain screens designed for high light-output projectors simply won't work with a CRT's low light output.
The color scheme of the home-theater room plays a role in picture quality as well. Certain color schemes can enhance the perceived contrast of the picture, reduce reflections, and won't alter the projector's color accuracy. An all-black room is optimum, but may not suit the tastes of some family members. That's one reason why a dedicated room or basement works so well for a front-projection system; the room's acoustic and visual characteristics can take priority over other considerations. Even if the room must serve multiple purposes, you can still achieve an aesthetically pleasing and technically correct design with a mix of black, dark red or burgundy, and dark gray.
The screen end of the room benefits the most from being blacked out. White or even light colors on the walls will reflect light from the screen, which reduces contrast ratio. This difference between light and dark is what gives the picture "snap" and depth. In addition to reducing the picture's actual contrast ratio and making the picture look "washed out," reflections reduce the apparent contrast ratio.
Blacking out the area surrounding the screen is especially important with DLP and D-ILA projectors because these projectors produce "light spray" around the projected image. This stray light creates a large light-gray border around the screen area that is distracting and decreases the apparent contrast ratio. Blackening the area around the screen makes a startling improvement in picture quality.
If you have a substantial budget for creating a theater-like environment in your home, companies such as Acoustic Innovations (www.acousticinnovations.com) design and build room treatments that provide the best acoustic and visual environment while maintaining a visually pleasing décor.
Uncontrolled ambient light is the enemy of picture quality with two-piece front projection systems. This is particularly true of CRT-based projectors because of their low light output. Even a little ambient light robs the picture of its depth and contrast. So-called "blackout" drapes are essential for watching a front-projection system during the day if the room has windows. And it goes without saying that the lights should be off while watching.
Your theater room should have some provision for low-level lighting. Once your eyes are dark-adapted, the last thing you want is bright lights while changing sources or making adjustments to your system. Wall sconces and fiber-optic lighting on the floors or ceiling can add a touch of class to the overall design of the room, as well as providing just enough light for specific purposes. For example, fiber-optic lighting placed in the carpet along the edges of the seating area adds to the feeling of being in a real movie theater, and also will make it easy for someone to leave the room unobtrusively if necessary.
Ceiling or Floor Mount? Front or Custom Rear-Projection Setup?
Another fundamental decision is whether to position the projector on the ceiling or floor. In my experience, mounting on the ceiling works better for several reasons. First, this allows the projection screen to be mounted more in line with a seated viewer's line of sight. With a floor mount, unless the projector is elevated by two to three feet, the projection screen must be mounted fairly close to the floor. A projector mounted on a conventional 8'-10' ceiling allows the screen to be 3'-4' from the floor, which presents a more comfortable viewing angle.
Second, floor mounting a projector invariably consumes the best possible seat in the room-front-row center. Third, if the system will also be used for high-performance music playback, placing a large acoustically reflective object between you and the loudspeakers will inevitably degrade sound quality, particularly soundstaging. Fourth, floor-mounted projectors, even if they are in custom-made coffee-table-like enclosures, are easily bumped, which can throw the projector out of alignment (particularly with CRT projectors). Finally, all projectors are noisy; a ceiling-mounted unit will emit less fan noise into the viewing area than a projector located right in front of you.
Before you mount a projector on the ceiling, you must determine that the mounting position is within the projector's throw distance, or distance from the screen that will still allow proper focus and image size. Fixed-pixel projectors usually have zoom lenses that let you dial-in the correct picture size over a range of distances.
The fans in DLP and D-ILA projectors are considerably noisier than those in CRT projectors because the bulbs run hotter and need more cooling. Depending on the throw distance and the room's length, you can sometimes position the projector behind the back wall and project the image through a hole slightly larger than the lens. A Plexiglas cover can completely isolate the viewing area from any fan noise.
Although I've concentrated on front projection, you should consider rear projection if you have the space. A (straight throw) rear-projection system works the same as (very much like a) front projection setup except that the projector is positioned behind the screen. Rather than using a white reflective screen, custom rear projection screen materials are available from a variety of screen makers. uses a lenticular screens similar to those in rear-projection televisions. Picture quality is comparable to front projection, and with fixed-pixel projectors such as DLP and D-ILA, rear projection confers the advantage of confining the light spray behind the wall housing the screen. Rear projection also keeps fan noise out of the theater room. Keep in mind, though, that rear projection requires a good-sized room behind the screen that often can't be used for any other purpose. Some rear-projection systems use a mirror system to reduce the space requirements, but these are expensive and still consume valuable real estate.
Making the leap to a front-projection home-theater system requires a serious commitment. But the rewards are as great as the challenges. There's simply no other way to get film-like images of a size that approaches the movie theater. Front projection done right delivers a vastly more involving and absorbing experience than is possible with any other video-display technology. Once you've enjoyed a movie on an 84" wide screen in your home, there's no going back.
This article has just touched on the highlights of what goes into a successful front-projection home theater. Before making a purchasing decision, I advise you to do your homework, and then contact a professionally-trained custom installer to design and install your projector and screen. The Custom Electronics Design and Installation Association (CEDIA www.cedia.org) is an organization that helps train custom installers in the finer points of home-theater installation, and is a good place to start your search for a skilled dealer to help you realize your home-theater dream.
Regularly posted columns and articles related to video and/or home theater. These will not only be product related, but also tutorial in nature, intended to offer advice or guidelines for home theater setup. In some cases The Miller Channel will discuss video and/or display related technologies if something new and noteworthy comes to light.
Planning and Setting Up a Front-Projection Home Theater
(from The Perfect Vision Issue 39 November-December 2001)
© 2003 - 2008 ISFTV.com All Rights Reserved