A common feature of Expositions and Conferences is a presentation involving a speaker and an audience. Whether it be a keynote address, a business meeting, or a seminar, it is common for a presenter or speaker to address an audience. Typically the presenter will be on a raised stage, lit to be seen, and with a microphone and PA system to allow the speaker to be heard clearly. Often there will be screens and projection system to display a presentation, or perhaps a camera/projection setup to simul-cast the speaker on a screen. All of this may fall under the jurisdiction of the IA, and stagehands must be able to set up and operate the necessary support equipment.
Audio/Visual equipment uses a mix of analog and digital data signals. Light and sound are “analog” phenomena, but are often converted to digital formats as computer processors of various types are used throughout to modify, store, and transmit audio and video data. Signals pass through various devices, all using their own standards for connectors. Assembling a system will necessarily involve multiple components and connector standards. A theatre technician must be familiar with multiple connectors to assemble an AV system.
USB or Universal Serial Bus is a family of connectors to transfer data and power between devices. As technology advanced and devices became smaller, new connectors were developed. There have been at least 11 variations on USB connectors over the years. The three “Standard” USB types are the most common, and are mostly likely to be backwards-compatible with older equipment.
USB-A: the original Universal Serial Bus connector. Widely adopted, it was designed to be relatively compact and easy to connect and disconnect. USB-A is a data-only connector. It is fairly thin and hot-swappable, but can be somewhat fiddly to connect as it only goes in a socket when oriented correctly.
USB-B: General found on larger peripheral devices, such as printers and scanners or external drives. Unlike USB-A, USB-B is meant to be connected and disconnected only rarely. It is taller but narrower than USB-A.
USB-C: a significant upgrade to USB-A, USB-B, plus the various specialty USB ports developed for later devices; USB-C is meant to be a universal port replacing all of them. It is significantly faster than the original types, and is smaller and thinner so it fits in small devices. USC-C can carry both data and power, plus video and audio signals. Unlike other USB types, USB-C can be inserted either side up.
Early computers used a variety of proprietary standards to drive monitors. Eventually, common standards emerged, only to be quickly replaced as technology outgrew the capabilities of previous devices. Like USB, there have been a succession of display connectors to go with the standards, yet the older devices continue to be useful or the connectors are repurposed for new uses.
VGA: late 1980’s, the first de facto monitor standard. VGA referred to both the video standard and it’s 15 pin connector. As higher resolution versions of VGA were developed, they continued to use the same connector. VGA is an analog signal standard. The video signal is divided into five components, RGB and two sync channels. It was the default video monitor connector for decades, and could be found as an option on most computers and projectors. If a more advanced standard was not common between devices, the included VGA was often “good enough” for many purposes. VGA is still commonly found on projectors and other gear for backwards compatibility. Adaptors may be required to connect to latest model computers.
Note that VGA is a video only format. You must connect any audio feed separately if you want to use audio. This is commonly done using the ⅛"/3 mm Audio jack on a computer, the “headphone” jack.
DVI: 1999. Delivers a noticeably higher quality image than VGA. Depending on the exact version, DVI can carry digital video or both an analog and a digital signal. There are also mini DVI connectors found on older laptops, but adaptors are required to interface. It is also a video-only format, so audio must be connected separately.
HDMI: 2002. HDMI is able to transmit both video and audio signals. HDMI is meant to be a digital replacement for analog outputs, and has replaced VGA as a common monitor connection. It is common on laptops thanks to it’s thin profile.
Display Port: 2008. An advanced, compact, and multi-purpose port, Display Port can carry digital video and audio, but also USB and other data.
USB-C: as mentioned above, USB-C can be used for data plus both digital video and audio signals. Many untra-thin laptops, tablets, and phones have eliminated all ports other than USB-C, meaning many more dongles or adaptors must be carried to connect to equipment with older ports.
The previous connectors use copper wire to carry signals. A newer technology is optical fiber, which uses thin glass fibers to transport data in the form of blinking light. Fiber optics can transmit significantly more data at much greater speeds in much smaller cables. Fiber-optics work well over long distances with little signal loss. They are more delicate, so careful handling is a must. There are numerous connector types depending on manufacturer and required bandwidth. The most common in AV use are LC, ST, and SC.
HD (high definition) video can be carried at radio frequencies using coaxial cable. The most suitable type of coax for HD video is 75 ohm cable. There are two types of connectors commonly used for 75 ohm coax.
BNC: a quick-connect locking connector. BNC stands for Bayonet Neill-Concelman after the developers. It is preferred on professional equipment as it is quick to assemble yet very secure. For this reason, BNC connectors are also used for RGBHV analog component video on profession grade equipment, such as monitors, video processors and switchers. RGBHV stands for Red, Green, Blue, Horiz. sync, Vert. Sync.
F-type connectors: an older connector type, F connectors are suitable for more permanent connections, and is common on consumer grade gear. F-type connector is the standard connector for cable and closed-circuit TV. It is a cheaper connector than a BNC but decidedly not quick-connect. The connector is secured with a threaded nut.
PowerCON: unlike the other connectors, this is meant for supplying mains power to a device, and replaces less secure IED type connectors on many devices. The power whip locks securely in place, but can be disconnected for storage. Developed by Neutrik, PowerCONS are similar to Speakon connectors. The original powerCON Is a 20 amp connector.
The newer PowerCON True1 (pictured) is a 16 amp connector, but unlike the original can be connected under load.
Because of the multitude of connectors, a good set of adaptors a.k.a. 'dongles" is a MUST for conference work. A client may show up with any number of devices that you will be expected to make work. Depending on vintage, PCs and Chromebooks may output VGA, DVI, HDMI, Display Port, or USC-C, plus ⅛" phone for audio. Apple devices may use any of these, plus proprietary formats like Mini-DVI, Mini-DisplayPort, Lightning and Thunderbolt. Android and iPad have their own sets of specialty connectors.
A client SHOULD supply the necessary adaptors to fit their device to a common standard, but they often won’t. All too often, they expect the venue to supply the necessary interfaces. A set of common adaptors to mate with the inputs of the house projection equipment is a very good thing to have available!
Besides the electronics gear, setting up for a conference presentation also means assembling the physical equipment, the projector and screen.
The projector must be placed at the proper distance to fill the screen with the desired size image. This distance is determined by the Lens throw ratio. To determine the correct distance, multiply the screen width by the Lens throw ratio. For example, if you wish to fill a screen 10 feet wide with a lens throw ratio of 2, the projector must be placed 20 feet from the screen. If the throw ratio is 2.4, the required distance will be 24 feet. Zoom lenses have an adjustable throw ratio within a given range.
There are two types of screens, front projection and rear projection.
Front projection (FP) screens are designed to display a projection car from the same direction that the audience views the screen. Early black and white movie screens were silver, hence the “silver screen”. Color works better on white, so Front Projection screens are a highly reflective white to better show color images.
Rear Projection (RP) screens are engineered to pass an image through the screen material efficiently without showing a hotspot from the projector lens. They pass whatever light is cast on them from behind through to the audience. To get a clear image, there should be NO ambient light behind an RP screen. The less light, the darker the appearance. You can recognize an RP screen because it looks dark gray when no projection is cast upon it from behind.
FP screens work well when backstage space is limited. The projector can be placed out in or over the audience, but the screen is more sensitive to ambient light. The presenters must be lit in a way that keeps light off the screen. RP screens can be placed much closer to the lighted areas of the stage but require much greater backstage space to achieve the throw distance required.
No matter the type of screen, the audience should be able to view it. The average person sitting down is about 4 feet tall. Therefore, the bottom of a screen should be about 48” minimum from the floor to avoid the audience casting shadows on the screen.
Ambient light is unwanted light falling on the screen from the same direction as a projected image, from the front on FP screens or from the rear on RP screens. Ambient light can wash out projected images, making colors less crisp and turning blacks grey. Black in an image can never be darker than the amount of ambient light on a blank screen. Ideally, room lighting should be zoned to keep extraneous light off the screen while still providing appropriate light levels on the presenter and often on the audience.
The advantage of RP screens is it is often easier to keep the space behind the screen dark. Light from the front parts through rather than reflecting back at the audience so the presenter can be much closer to the screen without affecting the projection. However, RP screens are more expensive and required a much larger space behind the screen for throw distance.
One effect you will always run into is “keystoning”. A projector projecting a rectangle directly at the center of a screen will project a rectangle. However, projectors are usually mounted at table top level or from the ceiling. The distance to the top and bottom of the rectangle image is distorted into a trapezoid or keystone-shape due to the difference in distances to and bottom of the image.
There are several ways to compensate for the resulting keystone effect. You can counter-distort the original source image to compensate but this is difficult to do on the fly. You can angle the screen so it is square on to the projector. This is not always possible.
A high end approach is to use motors to adjust the physical orientation of the several elements of a complex projection lens to compensate. This gives the brightest possible corrected image, but is expensive to accomplish. This method works with analog film slides or digital image.
The most common method with digital projectors is to adjust keystoning digitally. This has the effect of altering the image itself, but it cuts off part of the projected field, rendering the cut-off part of the image black. The overall image is dimmer by comparison. Yet it is the easiest and cheapest to accomplish. Most projectors use this method built in.
Just like a sound system, a Projection system must be started in the proper order. It has to do with how computers boot up. When a computer boots, it checks what devices are connected, then mounts them as a recognized device. But if the projector isn’t on, the computer won’t “see” the device. Therefore, to "mount* a projector, you must first remove the lens cap (so you don’t melt it when the lamp fires) then start the projector (so it is present to be recognized), then start the computer containing the source image.
If you are lucky, the computer will usually “see” the projector and set it up correctly. Otherwise, you will have to adjust it manually. On Windows, try the
<Windows>+<p> hotkey combination to toggle on mirror display. On a Mac try “System Preferences | Displays | Arrangement”. Arrange the screens and make sure that “Mirror screens” is checked. On ChromeOS, use “Settings | Device | Displays”.
The projector itself may also need to be set up using the device menu. Most digital projectors can be adjusted for ceiling mount, tabletop mount, front projection, or rear projection.
You may also want to add a “confidence monitor”. A presenter will often be in a position where they cannot easily see the screen. They are either in front of the screen facing the audience or the screen may be off to a side. Adding a video monitor facing the presenter that mirrors the projection will greatly help that person.
In large meeting spaces, screens are often used to simul-cast the talent so they can be seen in close-up by the entire audience. Cameras provide a live feed to the projectors. Camera operators take their cues from the Switcher, who directed the cameras ops via headset. Operators need to be familiar with “PTZ”, i.e. Pan (swivel the camera right out left), Tilt (to the camera up or down), and Zoom (“push in” or 'push out" to get a close-up or a “long shot”). If there are multiple cameras, the Switcher will use a device also called a Switcher to select which camera feed to send to the projector.
Finally, remember that this is effectively a “performance” for an audience. The space will need to be dressed nicely before the audience arrives. Cables will need to be covered or taped down to prevent tripping. Skirts may need to be added to tables and to the projection screens to hide cables and the support framing structure. Storage crates will need to be stored out of sight.
Copyright © 2021 Mick Alderson