SOURCE: December 2003 issue · POSTED: 03/26/04
Imagine you’re attending a lecture on American landscape painters. You arrive early and stake out a prime seat about a third of the way back in the auditorium. The room is beautifully finished with a large rear-projection screen and a well-designed lectern. The presentation starts with a breathtaking shot of Thomas Moran’s The Grand Canyon of Yellowstone. You listen with rapt attention as the presenter begins the story of 19th-century landscape painters. Then it happens: You hear a horrible groaning noise in the ceiling as a distracting fan system comes to life. You lean forward and cup your ear to hear better until a late arrival decides the best seat is the one directly in front of you. His head manages to entirely cover the waterfall, the painting’s focal point. You lean to the right, still cupping your ear, thinking things couldn’t get worse. But they do. As the presenter dims the lights to show the image in better detail, she completely disappears from sight. In resignation, you lean back in your seat, listening in the dark as she describes the beauty you cannot see.
In this scenario, there’s nothing wrong with the presentation equipment or the quality of the AV installation, but there are significant problems that make the presentation environment unfit. It detracted from the presenter’s ability to communicate the message, which is the primary goal of every presentation, whether visual or aural. Even if the best equipment has been installed with great attention to detail, a presentation will fail if the presentation environment isn’t right.
The three biggest potential problems that often get overlooked are acoustics, sightlines and lighting. The common denominator is that each of these factors is often considered part of the building and not part of the AV systems. Too often, end-users think they can simply add AV equipment to an existing space and get an effective presentation environment. That would be nice, but it doesn’t usually work that way. These three areas need to be addressed to ensure an effective presentation environment.
Acoustic issues include room acoustics (sound bouncing around inside the room), mechanical noise control (the background rumble or hiss that typically comes from the ceiling) and sound isolation (noise from outside the room).
Room acoustics is concerned with the buildup of noise within the room from reverberation and echoes. Reverberation time is the amount of time it takes a sound to decrease by 60 dB, or one-millionth of its initial volume. Rooms with large volumes and hard surfaces are more likely to have problems with reverberation. By using fabric-covered seats, sound absorptive materials on the walls and high-quality acoustical ceilings, reverberation time can be improved. As a rule of thumb, a large space with a sound system used for spoken word presentations should have a reverberation time of 0.6 to 0.9 seconds.
Mechanical noise control addresses excessive noise from the mechanical systems that can adversely impact a presentation environment. This includes noise from the air handlers, duct-borne noise and vibration noises. When designing a space, keep the main duct runs outside the room and allow only branch ductwork to serve the room. Also, work with the design team to determine the Noise Criteria (NC) rating. NC curves are a measure of the ambient noise that should occur in a room when empty. The lower the NC rating, the quieter the space. In a large auditorium where people need to hear well, a rating of NC 20 to NC 25 is suggested. The mechanical engineer can design the HVAC systems to meet this noise level when the systems are in operation. Although it’s not technically part of mechanical noise control, carpeting can be used to eliminate footfall noise and shoe heel click noise heard within the room.
Sound isolation refers to the ability of walls, doors and windows to block exterior noise from intruding in the presentation environment. These noises could come from the next room, an adjacent corridor, or even vehicle or airport traffic. When planning the location of a presentation space, keep mechanical rooms and other noisy areas far away. In addition, make sure wall constructions extend from the floor to the floor or roof deck above, not just to an acoustical tile ceiling. Open spaces above acoustical ceilings provide an easy avenue for sound to travel. All wall openings should be sealed air tight to prevent sound from passing through. The exterior building envelope should be designed to minimize noise intrusion from exterior noise sources. A Sound Transmission Class rating of STC-55 is common for conference-room walls. The higher the STC rating, the better the noise reduction.
Another area that frequently plagues presentation spaces is sightlines. Your ability to see the presenter — and in some cases, such as videoconferencing, the ability of the presenter or camera to see you — is critical for a successful presentation environment. Issues include image size, viewing angles, screen location, camera/presenter viewpoint and structural obstacles.
When there’s an image-size issue in a presentation environment, it’s usually because the image is too small. The standard rule of thumb for sizing images is the four-six-eight (468) rule. This means the farthest viewer should be no more than four, six or eight times the image height away from the screen, depending on the material being viewed. This works for all screen aspect ratios.
Four times is for material viewed for inspection — a CAD drawing or a detailed map that requires close inspection. Six times is for detailed reading of things like spreadsheets or text with images. This is the most common size for presentation environments. Eight times is for general viewing — watching a movie or images with few words. No matter what the material, if you’re doing a presentation, the 468 rule applies.
The preferred viewing angle has the audience no more than 45 degrees to each side of the center of the image, creating a 90 degree “viewing cone” centered on the image. This cone can be expanded to 45 degrees off the edge of the image if necessary. By using the 468 rule and the viewing cone concept, it’s easy to establish a viewing area in any room that has a direct relationship to the size of the image.
Turning our attention to screen location, one important yet sometimes overlooked variable is how high the screen is off the floor. This depends on what or who may be blocking the view of the screen. If there’s a possibility that a short viewer will be seated behind a tall person, you have to raise the screen or think about staggered or sloped seating. When you arrange the seats to create a greater distance between the viewer and the head directly in front of the viewer, you can lower the minimum height of the projection screen. Using a ray diagram drawn to scale, with stick figures representing the tops of heads at four feet (standard seated height), you can quickly determine how high above the floor the projection screen needs to be to allow everyone a good view. Ultimately, using a combination sloped and staggered seating arrangement will give the best results as the space gets deeper. Also, don’t forget that the top of the image should be at least six inches from the ceiling.
Sightlines also must be considered with regard to the presenter’s ability to see the audience for questions or for a camera to see the participants of a videoconference. Typically, if the audience can see the presenter, then the presenter can see the audience.
Issues arise when locating the camera for videoconferencing. Ideally, the camera should be located as near to the horizontal centerline as possible so viewers at the far end don’t look up to or down on the near-end participants. The camera should also be placed as close to the image as possible to increase the perception of eye contact with the far end. There’s nothing worse than participating in a videoconference where everyone at the far end appears to be looking off camera because they’re looking at the displayed image of you rather than the camera.
Structural obstacles like pillars are a fact of life in many presentation environments. The first option is to orient the room to minimize the number of seats behind the column. The second option is to provide a display for people sitting in the blocked area. Flat-panel displays can be mounted on the column and display the same material as the main projection screen. Just use the 468 rule so everyone has a good view of the presentation material.
The last area, often deferred to the electrician, is room lighting. Issues include lighting zones and ambient light levels.
How many times have you seen a presentation room with a great, high-lumen projector and yet the image onscreen was not eye-popping? Once the lights are dimmed the image looks fine, but it’s not possible for the presenter to dim the lights on the projection screen without turning off the room lights. Current 2000-to 5000-ANSI-lumen projectors are bright enough to produce a great image on a screen partially lit by stray light, but not a fully lit screen.
When dealing with projection systems, you need to be concerned with the black level of the system. By designing a room with lighting zones that allow the screen to be darkened while the rest of the room remains well lit, you can achieve a good system black level that results in good contrast in the projected image. At a minimum, you should allow for three separate lighting zones: one near the screen so the lights above the screen can be dimmed or turned off to improve the projected image; one for the presenter so he or she can be seen while the lights on the screen are dimmed; and the last zone for the audience.
Another lighting issue is sunlight or exterior light competing with the projected image. It’s important to keep all of the unwanted light — anything other than the projected image — off the screen. Whether it’s manmade or natural, you need to think about how excess light will interact with the projection screen. It may mean adding blinds, eliminating windows, or reorienting the screen location. Another option would be to use rear projection or some other direct-view display. In a room that really needs high ambient light levels — for example, a videoconferencing room, which needs at least 50 to 75 vertical foot candles of light — you should consider direct view or rear projection.
Ultimately there’s no perfect solution for every presentation environment. That’s why it’s important to think about the presentation space and create a design that allows everyone to see and hear the presenter with the least amount of difficulty. Combining a well-planned environment with a good technical design translates to a great presentation environment every time.
Disclaimer: This article originally appeared in a content partner publication. ICIA/InfoComm reserves the right to modify articles for concerns regarding grammar, style and format.