Screen Savers: How to Have a Better Picture for Less $

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The intention of this article is to save you considerable money, while at the same time, afford you a better picture, all by selecting the right screen at the right location. Next to acoustics, screen selection is the most complicated element of the home theater design process, and least considered.

Screen Location
It all starts with location. Referring back to an earlier article in this series, we discussed how the number of seats dictates the room dimensions and that room dimensions dictate optimum speaker and listener locations. Once we determine these positions, we know that we want the sound to seem as if it is being created by the picture, rather than coming from in front of, below, above, behind or to the side of it. That said, we want the screen to be located about the same distance from us as the center channel speaker.

Screen Size
The size of the screen is more critical than you think. Sometimes clients will say that they want a 10’ wide screen even before the size of the room has been determined. Most want a screen that is too big for their scenario. Not only will too big a screen cost more dollars, but the picture will not look as good as it should. Screen size is driven by physics and human perception, and math formulas help determine what size is optimum. These equations are derived by knowing resolution versus visibility of picture element size, which is given by projection type, projected resolution, projector light output, lens- throw distance to screen, screen type and screen distance to viewer.

A screen must also be comfortable to watch. If it is too wide, you cannot see the whole picture at once and are forced to move your head side to side in order see all that is going on. The Society of Motion Picture & Television Engineers did extensive studies regarding this topic and determined that a 30-degree horizontal field of view is optimum for comfort and belief.

Imagine a room with a 10’ wide screen against the front wall. Now imagine another room with a 7’ wide screen, positioned proportionally closer to you. Both occupy the same 30-degree field of view. If the rooms were totally dark you would not know which was the larger sized screen, however, the smaller picture would look better and costs less. If you want a 10’ screen, you have to sit a greater distance from it to avoid seeing the picture elements. To do it right, a bigger screen means a bigger room, a bigger audio system, a bigger projector system and maybe a special lens. This adds up to a lot of dollars - wasted dollars if you are only entertaining a small number of people.

Perforated Screens
Perforated screens are designed for speakers, particularly the center channel speaker, to be placed behind the screen, out of sight. The idea of the sound originating from the picture while hiding the speaker sounds good, but in reality doesn’t perform well. Placing any obstacle in front of a speaker will distort the signal. Acoustically transparent screens they aren’t. Sure, sound gets through, but not the same sound as without. Different perforation types and different speaker distances will yield different frequency responses. Of course an equalizer can help, but it will never be the same and the L,C & R speakers need to sound the same to be believable. A better practice is to place the left and right speakers to the sides of the screen (without blocking anyone’s field of view), with the tweeters about 40” above the floor, the bottom of the screen also about 40” above the floor so the center channel is right below it. The picture and sound now nicely line up with your eyes and ears and offer cohesiveness. Don’t put the left and right speakers behind the screen. Not only will they sound bad, but you will not enjoy a proper soundstage because they will be too close together in relation to your distance from them.

Perforated screens also cause light loss due to the holes. This may not be much of a concern if you are planning to use a fixed pixel projector like DLP, LCD or LCoS, a screen less than 7’ wide, in a 100% light controlled environment. But if you don’t meet these criteria, you may be very disappointed in the poor dynamic contrast and/or brightness, or the cost of a projector that can make up the difference in light loss.

Picture resolution is another problem of perforated screens. Sit too close and you are able to see the holes, which impacts the resolution available to you. By the same token, if the picture elements that are projected onto the screen are near the same size as the holes or smaller, you’ll lose resolution. Figure that a perforated screen will not sound as good, will require a greater viewing distance, and a more powerful projector to overcome the loss in resolution and light. In other words, avoid perforated screens for high fidelity A/V applications.

Housing Types
Drop-down screens will run an additional $1,000 dollars or so over a fixed wall-mounted screen, but are great in rooms that are not dedicated theaters or where audio only playback is enjoyed at times. Flush mount drop-downs cost even more, but provide a screen that also hides its housing.

Material Types
We already covered perforated screens, but there are also screen finish options available for different applications. We won’t discuss screens intended for non-home theater applications and will assume you want a flat spectral response, optimum light output, etc. Depending on ambient room light conditions, screen size, projector type and capabilities, you may need to look at a screen material that is not matte white. Screens that will be used with higher ambient light can benefit from being gray like Stewart Filmscreen’s Grayhawk or even the darker gray Firehawk. These screen materials help black appear black and improve dynamic contrast. Such screens can also help lamp-based projectors by pulling their inherent ambient light down to an acceptable level.

High Definition Considerations

Those with HD systems should look for the new smaller grained screens coming out. Granularity size versus pixel size, particularly for scenarios that call for a screen 10’ wide or under, can be visible. When picture elements are near the size of the reflective granules on the screen, resolution is lost.
The visibility of pixel structure will likely be greater for a 1080p LCD than a 1080p DLP, hence a greater viewing distance.
You can view a larger image with 1080p than 720p.
Look for a screen gain of 1.3 or below for HD to avoid “hot spotting” at closer viewing distances for HD.
1.78:1 (16:9) is the standard aspect ratio adopted for HDTV. It also has an amazing capability of accommodating the other most prevalent aspect ratios used.

Summary
Hopefully you now have a new respect for the importance of screen selection. You can’t just guess at screen size, location and type. They must be calculated by someone who knows the numbers and the formulas. The screen should be located near the center channel, which will dictate its size, which will dictate the projector and screen material. With picture fidelity, too big = too bad!

Norman Varney is the owner of A/V Room Service Ltd.