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How to buy a screen
March 16, 2000,
Step Two: Select a fabric or screen type
Screen material pretty much all looks white from a distance. But different fabrics have different characteristics, and you should pick one that is best for your needs. To help sort them out, give some thought to each of the following issues:
Gain: An important performance factor for a screen fabric is what is called its "gain." This is a very simple concept. Some screen material will reflect light uniformly in all directions. When it does this, it is said to have "no gain." If a screen has no gain, the picture you see on the screen will look the same no matter what angle of view you have to the screen. So if several people are watching the picture at different angles to the screen, they will all see essentially the same picture at the same brightness level.
Screen materials that have high gain will reflect more light back toward the center of the viewing area, and less light toward people sitting on the sides of the room. When this happens, people sitting in the middle of the audience will see a bright picture, and those sitting toward the sides will see a dimmer picture. You can see this effect yourself; as you move from the center to the side of a field of view, you can notice that the picture gets dimmer.
Screens have different gain factors: some are very high gain, others are moderate, and still others are low gain. The gain rating is quoted in numbers such as 1.0 (or "unity gain"), 1.3, 1.5, 1.8, 2.0, 2.5, etc. As the gain number increases, the brightness of the picture intensifies when viewed head-on, and falls off more dramatically as you move from the center to the side.
What does all this mean to you? Well, if you have an audience seated in a long and narrow room, then using a high gain screen makes sense, as it intensifies the illumination in the area where your audience is sitting. However, if the audience is seated at wide angles to the screen, you want to use a low gain fabric so that those on the outside don't experience the dimming effect.
In the past, high gain screens were important because projector light output was relatively low. So any boost in image brightness was welcome. However, today's projectors are very bright indeed, and if you have a projector with sufficient light output, it is best to go with a no gain, or low gain screen since they give a more uniform picture over a wider angle of viewing.
Videophiles setting up the best possible home theater systems go for low gain screens. Some of the manufacturers have screen products that they designate as ideal for home theater. For example, the Da-lite Cinema Vision material is 1.3 gain, as is the Stewart Studio-Tek. Both of these have been popular for home theater use. However, Draper and VUTEC offer competitive fabrics as well.
Acoustical transparency. Another factor to consider is whether you need an acoustically transparent fabric. This is one that will allow sound to pass through it from a speaker mounted directly behind the screen. If you are setting up a surround sound audio system with a left, center, right, and two surround speakers, the center speaker can be placed directly behind the screen for its best effect. If you do not have an acoustically transparent screen, the center speaker must be placed above or below the screen to avoid distortion.
All four vendors make one or more fabrics that are acoustically transparent. The effect is created by perforating the fabric with thousands of extremely small holes. If you intend to mount a speaker directly behind your screen, make sure to mention to your dealer that you need an acoustically transparent material.
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