A/V Veteran

In Choosing the Right Projector for a WOW! Experience, we compared the merits of big-screen TV vs. video projection and covered the ins and outs of selecting the perfect projector. Now it’s time to delve into what it takes to choose the perfect screen to go with your new projector.

In Part 1 I mentioned the subject of screen-to-viewer distance vs. screen size, and how it might relate to image resolution. In theory you should be able to sit closer to the screen with a 4K source than with high definition at 2K. Since the distance vs. viewing angle results you get from most on-line calculators (including my favorite, myhometheater.homestead.com) assume 2K resolution, you can confidently use them for 4K sources, or even move a foot or two closer to see if this offers any advantages. But keep in mind that most of today’s “4K” sources have been upscaled at the production end from 2K originals. The 4K you see on your screen will present a finer pixel structure, and thus perhaps slightly smoother images than 2K, but likely no increase in genuine detail.

One downside to sitting closer to a screen is loudspeaker coherence. Your speakers probably flank the screen, and a multi-way speaker (such as a 2-way with a woofer and tweeter, or 3-way with a woofer, midrange, and tweeter) does need some distance from the listener for the output of these separate drivers to properly coalesce. But that shouldn’t be a concern unless you plan on sitting closer than 5-6 feet.

Screen Gain
Buying a projection screen is no longer simply a matter of choosing whatever color you want as long as it’s white. Even the all-white, solid surface screens most of us choose can be produced with different levels of screen gain, making some of them capable of producing brighter images, everything else being equal. A gain of 1.0 is considered neutral. A lower gain produces a dimmer image, while a gain higher than 1.0 produces a brighter one. A gain of 1.0 is defined as the light reflected from a standard surface material, typically either barium sulfate or magnesium carbonate.

But there’s no free lunch here. A projection screen is always passive. This “gain” is produced by configuring the screen material to enhance the brightness in the center while reducing it toward the sides. The “gain” is measured at the center of the screen only; when viewed off to the side the image will appear dimmer.

If the gain is too high, the center can also develop an obvious hot spot, with the center of the picture clearly much brighter than the sides. High gains screens might be helpful in some applications but should be avoided for home use. And high gain doesn’t affect just the brighter parts of the picture; it also raises the black level of given projector. I’d recommend gains of 1.0 to 1.3 (1.5 at most) for the most subjectively uniform image when viewed either from the center seat or at a reasonable distance off to the side. The larger of my two screens (a 96-inch-wide, 2.35:1, Studiotek 130 from Stewart Filmscreen) has a gain of 1.3 and I’ve never experienced either image uniformity issues or obvious hot-spotting.

Fixed or Retractable, Acoustically Transparent or Not?
Screens can be either fixed or retractable. Both perform equally well, but one or the other might be best in your situation. A retractable screen gets out of the way when not in use but can be pricey. Fixed screens are cheaper, but if you mount one in a high traffic area it could be susceptible to damage. When attempting to clean a screen, never use anything on it apart from the gentlest touch of a soft feather duster without first consulting the manufacturer.

There are other screen types apart from the solid, pure white variety. Acoustically transparent screens, either perforated or woven, allow you to mount the speakers directly behind them, as in a movie theater. But such screens can also affect the sound of your speakers. Though the change is usually small, limited to the highest frequencies, and possibly correctible with equalization, this might trouble viewers who value the sound as highly as the image.

Other concerns of acoustically transparent screens include slightly reduced screen gain, light passing through the screen and into the area behind the screen (perhaps even reflecting off of metal speaker cones to the point of them becoming visible to viewers — I once saw this in a movie theater at dead center!), and possible moire in the picture (most often in perforated screens, depending on the specific image and how the perforations interact with the projector’s pixel structure). All of these potential issues can be addressed with careful setup, but that might call for professional help.

Black Is Beautiful
Deep blacks are the foundation of any video image. The higher the black level on the screen the worse the visible contrast, producing a progressively flatter picture with less dimension. To see how deep blacks can be at their best in a given setup, turn off the projector and look at the screen in a fully darkened room. Ideally, you shouldn’t be able to see it at all. Then turn on a light anywhere in the room and look again. It should now be clearly visible. That’s how black a projected image can get on a conventional screen with the light on. Projectors don’t project black; projected black is produced by the absence of light. While projector limitations will always raise the achievable on-screen black level, the basic concept is still valid; room lighting is the enemy of any projected image. There’s a reason your favorite movie theater turns off the house lights during the show. And even then the exit lights can be annoying.

Curse the Light
Don’t be misled into thinking you can have it all (a brightly lit room and a stunning projected image) by those photos you often see of home theaters in glossy magazines (yes, even in ours). This isn’t deliberately misleading, but rather the only way to show a well-lit theater décor while at the same time showing a punchy image on the screen. Room lighting, with a conventional screen, seriously compromises a projected image no matter how much brightness the projector offers.

To address this issue there’s yet another type of screen: ambient light rejecting. This relatively recent development limits the reflection of light coming from specific directions. For example, it might limit light coming from the sides of the room (a lamp or window) while still passing the light from directly in front of it (such as from the projector itself, which is kind of important!). With such screens, however, light coming from the sides is still reflected around the room. Some of it (at reduced brightness) ultimately makes its way onto the screen where it reduces contrast. But while such screens are still a compromise in my judgment, the best of them can make video projection practical in environments where it otherwise wouldn’t work well at all. See How Do Light Rejecting Screens Work? for more on this subject.

Short-throw projection, in which the projector is located inches from, and just below, the screen, employs extensive picture processing to produce a properly proportioned image. These designs are often marketed and used as flat screen TV replacements; an example is the LG CineBeam projector we reviewed a couple months ago. Such projectors can offer advantages over a huge flat-screen set, but are typically more limited in screen sizes than conventional projector/screen setups. In fact, they’re most often sold together with a suitably-sized and compatible light rejecting screen, which means they’re also subject to the characteristics described above.