Home Theater Projection Screens

in Home Theater Design, Home Theater Projection Screens

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So your big TV might be nice, but when you are ready to really step up to all that a home theater can be, you need a projector and a screen. A screen that is measured in feet, not inches!

When it comes time to pick a screen, you have lots of choices. At the higher end, you have fully motorized screens with masking to provide you multiple aspect ratios. At the lower end you have manual pull-down screens.

Screen Size

Screen size is a hotly debated issue in the world of home theater. There are two main groups of thought on this subject. One is that you should try to get the best possible image for your space, even if it means the screen is smaller than your neighbors. The other is that you should try to get the biggest possible screen to maximize your theater and make your neighbors envious! The choice is yours, no one other than you can decide this issue; it must be what you are comfortable with and what your goals are in your theater.

For many folks, the way to determine the screen size is to go to your local movie theater. Find your favorite seat. Then, take some time and estimate the screen size, and the distance you picked from the screen. Often the ceiling tiles in the theater will be 2×4 feet, so you can count the tiles to estimate your seating preference. You might find that you like to sit at 1x or 2x the screen width. Knowing your personal preference, you can then take that home and determine your ideal seating distance for the screen width you will use.

You normally want the screen to sit so that the audience isn’t looking down, so your screen will sit higher on the wall than you might first expect. If you have one to two rows of seats, your screen will likely end up 24 inches from the floor of the theater. If you have many rows, do not be surprised if the bottom of the screen ends up several feet from the floor of the theater. Generally, you want the center of the screen to be no more than 15 degrees higher than the eye-level of the viewer, with the top of the screen no greater than 35 degrees higher than the eye-level of the viewer. Later in this course you will see a section that discusses viewing angles in relation to seat risers. Many projector manuals also include a chart that shows screen height calculations.

There are two related articles, in the Home Theater Learning Library, about screens and viewing. Check them out here:  Home Theater Viewing Angles and Home Theater Viewing Distance



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Screen Material

When it comes to the actual screen material itself there are several more issues to consider. The primary two of these are screen gain and viewing angle. You should account for both of these when choosing your screen. The screen gain, as you will read in a moment, is related to the brightness of your projector. This means you should make your projector and screen decisions together. A single screen will react differently for two different projectors, one brighter than the other, so keep this in mind.

Every screen these days has a listed ‘gain’, and can range from low gain to high gain screens. Most of the screens that are white and used in the home theater have a gain of between 1.0 and 1.3. Screens that are gray in color tend to have lower gains, including numbers lower than 1.0, although it is not unheard of for a gray screen to have a gain higher than 1.0.

The gain of the screen is measured by noting the reflectivity of the screen material. The measurement is in comparison to the amount of light that is reflected from a pure white board. A screen with a 1.0 gain has the same reflectivity as the white board, while a screen that has a 1.5 gain reflects 50% more light than the white board. Screens that are lower and have a gain of .80 reflect 80% of the light of the white board.

These gains above 1.0 are not to imply that light is “added”, only that by using technology in manufacturing, more light is reflected to the viewing position than would normally occur. If you shine a flashlight against a flat white wall, light will be reflected in all angles, even the ceiling and floor. Imagine now that the wall were created so that some of the light that would normally reflect to the ceiling and floor is now reflected towards you, it would seem that there is an increase in the actual light.

The measurement itself is taken at the brightest point on the screen, which is usually the center of the screen and perpendicular to the projection source. This is the peak gain of the screen. As you move to the side of center, you may reach a point where the brightness of the screen lowers. The distance you move with the picture remaining bright is the viewing angle of the screen. When you move beyond this point, the picture will continue to get dimmer as you move further and further to the side.

While it might seem that you should pick a high gain screen to get the brightest image possible, that is not necessarily the correct choice. The higher gain screens often have the smallest viewing angles; meaning people to the sides of the optimal viewing position will see a dimmer picture.

Screens that are very bright often do not reflect red, green, and blue light the same. So those sitting on the sides where the image is dimmer may also see a differently colored image than those in the optimal positions. A final issue with high gain screens is called hotspotting. Hotspotting means actual points on the screen (often the center of the image) that are visibly brighter than others. These issues tend to be more apparent on screens with a gain higher than 1.3.

Picking the screen color is yet another issue when you decide upon your theater screen. The two primary options are white and gray. The issue between these two is contrast. Gray is often called a high contrast screen. This is because the gray color ‘absorbs’ ambient light at a higher level than the white screens do. The net result of this is to increase the dark levels, while keeping the light color levels high. This makes white images look nice and white and increases the levels of the darks, with the end result of an increase in the contrast range of the image.

As projectors get higher and higher contrast ratios, the need for gray screens might seem to lower. Like so many other issues, the answer as to gray screens being needed any longer is based on different circumstances. If you have a room with high levels of ambient light, using a gray screen might still be your choice. While those in rooms with total control of ambient light will want to stick with a white screen.

Screen Aspect Ratio

During your planning, another screen issue you must address is the aspect ratio of the screen. The aspect ratio is the width in comparison to the height. It ‘defines’ the ratio of the rectangle of a screen and is written as width:height. The older standard television screen had an aspect ratio of 4:3 (also called 1.33:1). HDTV screens have an aspect ratio of 16:9 (also called 1.78:1). Widescreen movies have an aspect ratio of 1.85:1. Even wider is called Cinemascope, which has a common aspect ratio of 2.35:1.

If your primary viewing is HDTV material, then you will most likely have a 16:9 screen in your theater. The 16:9 screen is the dominant aspect ratio in the home theater. Most home theater projectors project images directly in the 16:9 format, allowing you maximum resolution. When viewing a widescreen Blu-ray or DVD on a 16:9 screen you may still have small black bars along the top and bottom of the picture, as the 1.85:1 image is slightly less tall than the 1.78:1 screen.

The Cinemascope aspect ratio of 2.35:1 is gaining momentum in home theaters. (Technically, there are many different aspect ratios. The ‘Cinemascope’ format may include 2.35:1, 2.37:1, and 2.4:1 aspect ratios.) Many movies are filmed in this aspect ratio, especially the “epic” films. As such, theater owners are reaching for this aspect ratio in their theater. One current drawback is that while there are many options for projectors that project 16:9 the options for projectors that project a 2.35:1 image are not available for consumers. This means the addition of external lenses to achieve the proper 2.35:1 image with the best possible picture quality. Regardless of the bit of extra effort, the 2.35:1 movement continues to grow and is here to stay.

Major Aspect Ratios

Above – Simple example of the three most used aspect ratios. The person in each frame is the same exact size, and the height of the example image is the same. You can see that you ‘lose’ much of the visible image as you decrease aspect ratio.

Aspect Ratio Examples

Above – The above example shows the main three aspect ratios on the left, and those same ratios applied to a still image (of Gollum from the Lord Of The Rings) simulating the amount of information visible in each aspect ratio.

Screen Masking

When viewing content that does not directly match the aspect ratio of your screen (for example, 16:9 content on a 2.4:1 screen), there are going sections of screen that are unused. These sections will generally appear dark gray on screen, often called the black bars. Black bars can be vertical on the left and right, or they can be horizontal on the top and on the bottom. To address these black bars, theater owners can install or create masking systems.

Some screen manufacturers have sophisticated masking systems. These masking systems actually change the visible aspect ratio of the screen material to match the aspect ratio of the content you are viewing. Instead of seeing a gray unused screen, you see deep black around the image.
Automated masking systems work by using small motors that move deep black material over the screen area that is not used by the projector for that aspect ratio. If you are using a 2.35:1 screen and are playing traditional 4:3 material, the sides of the masking system will activate and move the black material over the left and right sides, masking the unused screen section.

Many owners have created their own removable masking panels, held on by magnets, Velcro, or even friction fit, to function as masking panels. The DIY masking systems are very popular, as manufacturer masking systems can be quite costly.

Acoustically Transparent Screens

One last choice you will need to make for your screen is deciding whether or not to use the option called an acoustically transparent screen. These screens, often called AT screens, are designed so that sound from your front speakers can pass through the screen material itself. This allows you to place your front speakers behind the actual screen, and your center channel in the true center of the screen. Using an AT screen provides for much better audio placement, as the spoken voices will seem to come from the middle of the screen, instead of above or below the screen.

AT screens are fast becoming the standard for dedicated theater design, with the one requirement being enough room. When you choose this design, you will need approximately two feet (or more) of space behind the screen. When you build a theater with an AT screen, you have to design the room for the screen, which will be discussed later in this course.

So during your planning section for your screen, you need to decide on these issues: Screen Size, Screen Color, Screen Aspect Ratio, and to use an AT screen or solid screen. Lots to consider for your screen, so take each one at a time, and you will see how they all fit together. Later when you start to see all the theater photos, you will see the screens other theater owners have used.

 

Parts of this article were excerpted from The Ultimate Course on Designing and Building Your Dream Home Theater.