Aspect Ratio, Projector Placement
Continuing the design process, this section details the information collected, the decisions made regarding the final screen size for various aspect ratio content, and the projector and screen placement. It also confirms the previously discussed seat placement choices.
Choosing a Screen Aspect Ratio
Last Updated: 12/12/2024
Before deciding on projector placement, we need to decide on the screen size to place on the wall. Considering that we have a soffit and need space on the sides of the screen for the speakers, the maximum screen width we can go for is about 9-9.5 ft. Given that content is available in multiple aspect ratios, I wanted to choose an aspect ratio that prioritizes the most often viewed content. For this theater, I considered these three aspect ratios.
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4x3 (1.33:1)—Standard definition legacy TV (sometimes IMAX)
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16x9 (1.78:1)—HDTV (Also can lump 1.85:1 into this)
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2.35:1—CinemaScope movies (also 2.39:1/2.41:1 can be lumped here)
Two common methods for displaying multiple aspect ratios on a single screen are CIW (Constant Image Width) or CIH (Constant Image Height). The choice of which one to use partly depends on the wall layout, but perhaps more importantly, it depends on what type of content is most likely to be displayed and how one wants to prioritize the viewing of each of the aspect ratios.
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Figure 1. Constant Image Height (CIH)
With CIH, the widest image format determines the display height (Figure 1). Therefore, in this case, CinemaScope is the largest image displayed. CIH is typically preferred when:​
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Most of one's viewing content is CinemaScope
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When a viewer wants CinemaScope content to be the most immersive
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Typically, the screen can extend to the edges of the front wall (usually with an acoustically transparent screen).
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The allowable screen height of 16:9 limits 2.35:1's screen size.
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Figure 2. Constant Image Width (CIW) except for 4x3 Screen
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Ideally, the tallest format should set the screen width for the CIW format. The tallest format is the 4:3 format, but since 16:9 is much more pervasive today, the 16:9 aspect ratio was used to set the screen height. As a result, 16:9 content has the largest screen area, 2.25:1 content has black bars on top and bottom, and 4x3 content has black bars on the sides and is technically not a constant width. CIW can be preferred when:
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The majority of viewed content is HDTV
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The viewer prefers to have the experience optimized for 16:9 content.
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When the front wall arrangement cannot accommodate large enough 16:9 content on a CIW screen, it typically has narrower screen walls.
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Optimizing HDTV and streaming content for 16x9 viewing was prioritized for this theater build. The goal was to make 16x9 content as large as possible. Additionally, due to the width limitations imposed by placing speakers to the sides of the screen, optimizing for CinemaScope would have made 16:9 content too small. Therefore, a 16x9 CIW screen was the best option for this build, and the maximum size that fits the room was determined to be a 115-inch diagonal screen.
Projector Placement
Last Updated: 10/112024
Before finalizing the room layout, it should be confirmed that the chosen projector can be positioned in the room to produce the desired image size. Different projector designs have a specified range of 'throw distance' requirements. Additionally, projectors can usually be placed within a specified distance above or below the center of the screen using their 'vertical lens shift' capabilities.
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During the planning phase, I did not decide on the final projector selection until later in the project. In this case, one should gather throw-distance and lens-shift capabilities for the most likely candidate projectors. For this home theater, the leading candidates were the Panasonic PT-AE4000 and Epson PowerLight Home Cinema 8700UB. The key determinant is whether the projector can display the desired image size when mounted at the desired distance from the screen. This is visualized in Figure 3.
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​According to the 8700UB's manual, the projector has a throw range of 3 to 62 feet and can project a 30 to 300-inch image. However, the projected screen size depends on the distance from the lens to the screen. The 8700UB manual provides tables that specify the range of screen distances possible for eight screen sizes, and one could easily extrapolate from this table whether the projector will fit into the room.
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Many projectors specify a Throw Ratio, and if they do, then one can use the equation for Throw Ratio in Figure 3 to determine if the projector can create the desired screen size. The Throw Calculator from projectorcentral.com is an excellent resource for determining a projector's placement requirements and limitations. The calculation for the 8700UB indicates a range of distances that would suit the desired screen size. For my 115-inch screen, the projector must be placed between 11.2 and 23.9 ft. from the screen. This is within the plan to put the projector ~14 ft from the screen.
Figure 3. Projector Distance and Lens Shift
Figure 4. Drawing showing lens offset from center.
(© 2010 Epson America, Inc. CPD-28061)
The next consideration is whether the projector has enough Lens Shift. This is the ability of the project to shift the image vertically and horizontally to center the image on the screen in cases where the projector cannot be positioned at the center of the screen (which is in most cases). The projector was to be ceiling-mounted, positioned roughly near the top of the projection screen, and centered horizontally on the screen. The 8700UB's vertical lens shifting capabilities allow the image to be shifted to the full image height. The projector should be placed below the top of the screen, which can be accommodated with a typical projector mount.
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An important point to note is that typically, projectors have a limited horizontal lens shift range, so it's essential when mounting the projector to align the projector's lens to the horizontal center of the screen. Since the 8700UB lens is (annoyingly) not located in the center of the projector (see Figure 4), it's necessary to measure the lens offset from the project body's center and compensate by this amount when determining the projector mount location. This ensures that the projector's lens is optimally centered horizontally to the screen.
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Projector Sound Isolation Hush Box
Last Updated: 09/04/2024
Another aspect of projector location is its impact on background noise in the room. An in-room projector will determine the noise floor of the room. Ideally, the projector should be enclosed to prevent fan noise from reaching the listener. In our theater, we just hung the projector. This was one of (perhaps) many less-than-optimal decisions made.
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A better way to handle the projector's fan noise is to build a box around the projector. This box is more complex than a simple box, as shown in Figure 5. The hush box needs to have the following additions:
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The projector needs adequate ventilation, so the box should have some way to input air for cooling and output exhaust air.
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The box should have some insulation to reduce sound transmission.
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If the box is to be sealed, a glass plate must be placed in front of the projector's lens.
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The box needs holes to pass the cabling to/from the projector
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If a soffit is planned near the projector, the hush box could be integrated into the soffit (which would have been a better choice for this room). An even better option is to place the projector completely outside the room.
Ultimately, there was no space outside the theater for the projector, so I chose not to build a hush box. The reasoning mainly was to avoid extra time and effort. In hindsight, even though the fan noise is not that loud and only noticeable during quiet interludes, we should have paid more attention.
Figure 5. Hush Box Concept for a Projector (top view)