How to choose a projection screen? - Rapallo New Zealand :: Home Theatre & Hifi | Design & Installation
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When it comes to setting up a great video projection system in your home theatre, the screen is nearly as important as the projector. A white wall or sheet simply won’t do, except in a pinch as a temporary stopgap. There’s no substitute for the real thing.

But choosing the right real thing requires research, together with examination of your individual needs.

How tightly can you control the room lighting? How big do you want the image to be? What shape screen do you want—that is, what aspect ratio—and do you want a screen that can mask off the unused portions when the source is a different aspect? Can the screen have a fixed frame, or do you want it to be retractable? How much gain should the screen have? Which screen will best match your projector? And last but not least, how will 3D affect all of these other considerations?

I’ll attempt to clear away some of these cobwebs, but if serious questions persist, there are skilled custom installers in most parts of the country who, for a price, can help you select the right screen and install it properly. But even if you hire an expert, you’ll be miles ahead with a little knowledge of your own.

Room Lighting

How much room lighting should you have for the best projection experience? The answer to that was once obvious: A projector can do its best only if the room is as dark as possible. The following always holds: Projectors do not project black; black is simply the absence of light, either from the projector or from any other light source in the room. In the ideal case, with both the room lights and the projector turned off, the room should be so dark that you can’t see your hand in front of your face. In addition, the walls, ceiling, and floor should be as dark as possible. Black or very dark grey are ideal. This reduces the chances for light from the projected image to reflect back on the screen and degrade the picture.

But let’s get real. While a bat cave is the best environment for video projection, not many videophiles can or will go this far. But a subdued environment—neutral greys or beige on the walls, floor, and ceiling, plus lights out when viewing—is worth aiming for. There are also glass-fibre matt screens and grey or black screens that can minimize the negative effects of room reflections and room lighting (Rapallo Indigo Screens or bespoke options-discuss with our Rapallo experts).  If total darkness simply isn’t possible, you can cleverly set up spotlights that won’t throw any light on the screen.

So what about those fancy custom installations you see in these pages and elsewhere that show cheery room lighting and a bright, well-saturated image on the screen? Sorry, the screen images in those shots are almost invariably Photoshopped in. Otherwise you’d see a washed-out picture or a blank screen. The pictures are there to show off the room décor, not to demonstrate that you can have it all with the room lights set to stun. There’s a reason your local multiplex turns off the house lights during the show, and it isn’t just to save money on their electric bills.

Configurations

Your screen choices include fixed-frame screens that either mount on a wall or on an optional stand, retractable screens, and super-wide, CinemaScope-shaped screens—either flat or curved (bespoke-discuss with our Rapallo experts). You may use the latter with an anamorphic lens and special processing to display 2.35:1 films with no black bars. Such a screen will have bars on the sides with standard widescreen (16:9) or older (4:3) movies, but they can often be fitted with adjustable powered masking to blacken them. Various degrees of masking are also available for the more common 16:9 screens when you show 2.35:1 or 4:3 sources. At the low end of the price range, a do-it-yourself screen paint kit can run you under $200. At the high end, you can pay over $20,000 for a 10-foot-wide, 2.35:1 CineCurve screen with powered masking.

Screen Size

The dimensions of the wall where you plan to install your screen will limit the screen’s width and height. For the best sound and optimum surround speaker placement, the combination of screen size and room length should be such that you can sit a reasonable distance from the screen and at least a few feet from the wall behind you, if possible. You’ll need more room at the rear if you plan to use more than one row of seats, either permanent or temporary, for occasional guests.

You’ll also want to check your projector’s throw distance to be certain that it can fill the screen at the available room length, including a foot or so to spare for the projector connections—and any calculation errors. This may limit the size screen you can accommodate. For various reasons, it’s often best to locate the projector as far from the screen as its zoom range will allow. You should also confirm whether the projector and screen manufacturer’s specs refer to screen size by width or diagonal; a wrong assumption could result in an unpleasant surprise. If you’re planning on the most common screen shape, 16:9, it’s useful to know that the diagonal measurement times 0.87 equals the screen width.

Just how far from the screen should you sit? The farther away you are, the smaller the viewing angle—the angle the screen covers in the viewer’s front field of vision from the far left of the screen to the far right. At larger angles, the image will be more immersive but also more likely to reveal picture flaws and artefacts —a problem, in particular, with standard-definition sources. Recommendations for the optimum projected viewing angle generally range from 30 to 40 degrees. You can alter this angle by changing the screen size, the viewing distance, or both. Which of these you choose will depend on your projector’s brightness, the size of your room, and how far you need to sit from the front speakers (and how far apart they can be) for the drivers and soundstage to gel properly.

There’s a Website that offers a handy tool you can use to calculate your viewing angle from the seating distance and screen size: myhometheater.homestead.com/viewingdistancecalculator.html. From this site, I derived the following rule of thumb: A distance of 1.86 times the screen width will produce a viewing angle of 30 degrees; a distance of 1.36 times the screen width results in 40 degrees.

Also keep in mind that as the screen gets larger, the image will dim in nearly direct proportion to the increase in screen area, all else being equal. Projection lamps dim with age, often by as much as 30 percent in the first few hundred hours. So your best bet is to not “overscreen”. That is, be conservative in the size screen you choose, particularly if, like me, you prefer brightness levels at or a bit higher than the 14-foot-lambert minimum CEA/CEDIA specification.

Screen Gain

The brightness of the projected image depends not only on the projector and the size of the screen, but also on screen gain. Say what? A screen is a passive device. How can it have gain? It doesn’t, really. Higher-gain screens reflect more of the light incident on them toward the center of the viewing area, producing a dimmer image off to the sides. A screen with equal reflectivity in all directions, by definition, is said to have a gain of 1.0. A higher-gain screen sacrifices reflectivity to the sides for greater brightness in the center.

While some videophiles swear by high-gain screens, particularly those who demand a really big picture, our recommendation is to keep the gain between 0.9 (yes, there are screens with gains less than 1.0) and 1.3. The lower end of this range should offer satisfying brightness with most modern projectors at screen widths of up to 8 feet wide (gain 0.9 to 1.1). If you go larger or like a brighter (but not overbearing) image, you might consider a gain of 1.3.

But we’re talking about 2D here. 3D projection is dimmer, which means that other considerations come into play. Judging from the relatively affordable 3D projectors we’ve seen so far, you’ll want a gain of at least 1.3 and a screen no more than 7 to 8 feet wide. Go much larger than that, and you’ll need an even higher-gain screen. But be aware that the higher the gain, the higher the likelihood of hotspotting and other performance issues.

While the early home 3D projectors we’ve seen use active glasses, future models that employ less expensive passive glasses might well make it to market. If that happens, you’ll need a special silvered screen that cannot (at present) be either perforated or retracted. And this screen will compromise 2D performance, so video purists will need a standard retractable screen positioned in front of the fixed silvered screen. Because of that impractical scenario, we currently recommend against home 3D projectors that use passive glasses.

 To Perf or Not to Perf

Some screens are more or less acoustically transparent. They use either a woven material or a material with scores of tiny micro-perforations. You can position your center-channel speaker (or all of your front speakers) behind them. While it’s certainly an advantage for dialogue to come directly from the center of the picture, such screens involve significant video compromises. Some light will pass through them, so they lose brightness. They can also affect resolution, and interaction of the perforations with the pixels in the image may even produce moiré patterns. If you insist on an acoustically transparent screen, we strongly advise that you deal with a trusted custom installer who has experience dealing with these issues.

Wrapping It Up

Our recommendation if you’re just starting out is to choose your screen size based on the desired viewing angle, your room, and the characteristics of your chosen projector. A non-perforated, 1.3-gain, 16:9 screen no more than 9 feet wide will be your safest choice. You can even go a little smaller if you anticipate using an affordable 3D projector. If the screen is retractable and you plan to mount it on the ceiling rather than the wall, make sure the drop (the black material above the screen) is sufficient to bring the screen down to your desired height.

It should be obvious that making the right decisions here will involve more variables than just choosing a projector. You may even need that custom installer to help install the screen. In any case, the choice of the right screen can go a long way in helping you get the most out of your big-screen experience. The Rapallo Team is more than happy to help you decide on the best option for your individual situation and for your budget.

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