The Science Behind Presentations: Equipment

 

CONTENTS

 

LCD Projectors

A projection of a PowerPoint presentation or a video will often compose the sole visual component of your presentation. It is important that you understand and are comfortable with the projector you are using. Otherwise, you might present a blurry or poor quality image without knowing how to fix it, or you might fail to work the projector altogether. Take the time to acquaint yourself with the device and all its options before relying on it to demonstrate your work.

How Do LCD Projectors Work?

When you turn on the projector, a lamp shines light through a filter. This filter is polarizing, meaning it only accepts the light from the lamp while blocking all other light. The light then hits a number of dichroic mirrors-- mirrors which only reflect certain colors in the light spectrum. In this case, the mirrors separate the light into red, blue, and yellow.

Each of the three colors strikes a different LCD panel. They are then recombined in a dichroic prism and sent through the lens onto the projection surface. The amount of light which each panel allows affects the color that is projected. In other words, the three panels control red, blue, and green light separately to produce the color you ultimately see on the screen.

What to Know for Presenting

Whether you are purchasing or just using a provided LCD projector, you should be aware of the types of projectors available and the different options that each projector offers. Projectors vary in size, resolution, brightness, and contrast, so you should try to pick the projector best suited to your presenting needs.

Size

Three main types of LCD projectors exist, divided primarily by size and power: ultralight projectors, conference room projectors, and fixed installation projectors.

Ultralight projectors are the smallest and the most portable; some can even fit in a briefcase and weigh less than five pounds. These devices are ideal for the traveling presenter who cannot expect an adequate projector in every location or who likes to use his own, personalized equipment. However, the lightest projectors can be expensive.

Conference room projectors are the most common. They weigh ten to twenty-five pounds, so they are still mobile to a degree, and they are better for large rooms than ultralight projectors. They also tend to come with extra features such as a laser pointer or a remote mouse.

Fixed installation projectors are those that are permanently installed in an auditorium or presentation hall. They are the largest, the brightest, and the most powerful.

Resolution

The number of pixels on the screen determines the resolution, or clarity, of the picture. An unclear picture can make the details of your presentation unreadable, so you should strive for the best resolution possible. Many projectors work with different resolutions, but they all have a native resolution at which they work best. For the best image, before a presentation, figure out the projector's native resolution and match your computer's resolution with it.

Generally, the higher the resolution, the more the projector costs. Purchasing a projector requires you to balance the money you are willing to spend with your resolution needs. SVGA projectors, with a resolution of 800 x 600 pixels, are cheap and adequate for most PowerPoint presentations, but detailed images will not be clear. XGA projectors (1,024 x 768) are the most common and show more details; they are precise enough for most presentations. SXGA projectors (1,280 x 1,024) and those with even higher resolutions work with high-end PCs and show very exact details, but they are the most expensive.

Brightness

Brightness is measured in ANSI lumens; the more lumens, the brighter the projection. In most cases, a projector with a brightness between 1,000 and 2,000 lumens should be sufficient. However, in rooms with a lot of ambient light, you might need a brighter image (2,000+ lumens) to stand out. In addition, you should use brighter projectors for large audiences in large rooms.

Contrast

Contrast is the ratio between the brightest and the darkest portions of the image. Higher contrast creates better quality images, so a contrast ratio of at least 250:1 is desirable. Contrast also helps to display the image against ambient light. In brighter rooms, seek projectors with higher contrast ratios.

Other Considerations

Before you buy or use a projector, you must make sure that your computer connects with it. Otherwise, you will need a connector cable or an adapter. You also should consider the lamp; a stronger lamp will produce a brighter image, but probably will not last as long. Lamp life lasts between 1,000 and 4,000 hours, and lamps can cost hundreds of dollars to replace. Lamp power is thus a trade-off between picture quality and life/cost.

The Screen Door Effect

Electronics control each pixel on the LCD panel. Light does not shine through these electronics, so little black boxes may appear around each pixel on the image. The result is a picture that looks like someone has placed a fly screen on top of it. Higher resolution projectors generally do not suffer from this problem, as they reduce the size of the black lines to the point that they are invisible. However, if higher resolution is not an option, de-focus. This may seem counter-intuitive, but if you can manage to blur the black lines without making the pixels overlap, the screen door effect will not be as pronounced. The picture will naturally appear more fuzzy, though; it is up to you whether you prefer the sharper image with lines across it or a hazier image without lines. If you encounter the screen door effect, you should adjust the resolution until you find the picture which appeals the most to you.

Projection Screens

Projection screens render all your hard work visible to the audience. Without the right screen, your data may appear unreadable or hazy even with the best projectors. As a presenter, you might not have much choice regarding the selection of the venue's screen, but you should still familiarize yourself with the advantages and the pitfalls of each type.

Types of Projection Screens

Your one option in choosing a projection screen as a speaker might be purchasing a portable screen. These can be wrapped up and carried with ease, and they are ideal for travelling presenters who want to ensure they have a surface on which to project their message.

Manual screens are versatile and easy to use; these are the screens you know from classrooms. They allow you to lower and lock the screen as you desire and can be rolled securely after use.

Fixed frame screens are permanently installed screens used in many meeting areas.

Electric screens are mounted to the wall, floor, or ceiling, and extend via electronic controls. They require a more complex installation and a power source to operate.

Gain and Viewing Angle

The surface type of screens can vary as well. Pay attention to both the gain and the viewing angle of the fabrics. Gain measures the reflectivity of the screen. The gain ratio is the amount of light the screen reflects compared to an ordinary white board (so a gain ratio of 1.0 means the screen reflects the same amount as a white board). The Half Gain Viewing Angle is the angle from which the screen will appear half as bright as it appears head-on. Higher gain screens generally have lower viewing angles, so while they will seem brighter from a central viewpoint, they will quickly drop in brightness for audience members seated at more angled perspectives to the screen. For conference rooms in which most people see the screen from a relatively straight angle, high gain is desirable; otherwise, the wide viewing angle of lower gain screens will better suit the audience.

Front Versus Rear Projection

With front projection, the projector is set up in front of the screen. This requires a projection room or a platform on which the projector can sit. Also, the light must have an unobstructed path, and it must be shined at a perpendicular angle to the screen. If the light path is not perpendicular, keystoning occurs, the effect where the image appears wider at the top than the bottom and resembles the keystone of an arch. Front projection allows for a wider viewing angle than rear projection, but it is more susceptible to ambient light.

With rear projection, the projection unit is set up behind a translucent screen. The image must be reversed so that it faces the correct direction for the audience. The projector can be placed at the very middle of the screen without worry of audience obstruction, so keystoning is not a problem. In addition, ambient light will not wash out the image as much, but the viewing angle is narrower than front projection provides. Also, there must be space behind the screen to fit the projection device, and rigid rear projection screens can be more expensive than front projection screens.

What to Do About Ambient Light

Ambient light refers to any light that does not come from the projector, and it is the bane of many presenters who want to project clear, vivid images. A front projection screen reflects all light that hits it, regardless of whether or not the light comes from a projector. The more ambient light is present, the more washed-out the image will become, so ambient light should be minimized. Roller shutters, black-out blinds, and heavy curtains can keep out sunlight; regular curtains are usually too thin. If possible and practical, you should turn off all the lights in the room. If some interior lights must remain on, you should set up the projector as far away from them as possible.

Microphones

No experienced presenter would understate the value of a good microphone. If the audience cannot hear you clearly, they will probably fail to absorb your message regardless of the quality of your visual presentation. Importantly, though, not all microphones are alike. Certain microphones are best adapted for certain situations. Before presenting or purchasing a microphone, you should know what kind you will need and how best to use it.

How Do Microphones Work?

Essentially, microphones convert acoustical energry-- sound waves-- into electrical energy-- auditory signals. A piece of metal called the diaphragm, usually located within the microphone's head, vibrates when sound waves hit it. This starts a chain reaction wherein other components of the microphone vibrate. These vibrations translate into auditory signals. Eventually, speakers will re-convert the auditory signals into the sound waves that we hear.

What to Know for Presenting

As with any kind of equipment, microphones vary in many features. Two main types, dynamic and condenser, exist, but each of these includes microphones of different directionality, impedance, and frequency response.

Types of Microphones

In dynamic microphones, the vibrating diaphragm causes a coil to move back and forth along a magnet, creating a current. These microphones are good for general-purpose use. They are sturdy, well-suited for high volumes, and require no batteries nor external power.

Condenser microphones use a capacitor, two plates with a voltage between them. One of these plates is the diaphragm. As it vibrates, the distance between the plates changes, increasing and decreasing the capacitance and thus creating a current. The microphones are more responsive and sensitive than dynamic microphones; they pick up subtler sound differences but are not as suited for high volumes. They also require a battery or external power source.

Directionality

Directionality dictates from where a microphone picks up sounds. Omnidirectional microphones pick up sounds from all directions. They are good for capturing ambient noise or situations in which the microphone is fixed but the sound source is moving; however, they are not best for most presentations.

Unidirectional microphones pick up sounds primarily from one direction. Most handheld microphones have this directionality. These help to focus on one subject while cutting out ambient noise, so they are ideal for most presentations. They also can pick up sound from a greater distance. However, the speaker must be careful to keep the microphone pointed at himself, as the directionality can be very precise.

Bidirectional microphones pick up sound from two opposite directions. They can be useful for interview settings, but they are rarely applied elsewhere.

Impedance

Impedance measures the opposition a device has to an AC current. The lower the impedance, the better sound you will achieve. Microphones with high impedance-- 10,000 ohms or more-- will result in worse sound quality, especially when longer cables are used. An impedance of 600 ohms or less is considered low and ideal.

Frequency Response

Microphones respond differently to different frequencies; they exaggerate some while reducing others. In other words, as the speaker's voice naturally fluctuates in frequency, the microphone will emphasize some fluctuations above others. A flat frequency response, or one with which the microphone responds equally to all frequencies, is generally optimal, but it is not possible. Still, you should try to find a microphone with a relatively flat frequency response. Keep in mind that condenser microphones usually have flatter frequency responses than dynamic microphones.

In some cases, though, you might actually benefit from using a microphone that does not have a flat frequency response. For example, if you are speaking in a location that will have a lot of non-vocal background noise, you might want a microphone that emphasizes the frequencies of the human voice. Take into account the specific circumstances of your presentation when choosing your microphone.

Tips for Use

Microphones are there to amplify your regular voice. Speak normally, adjusting the microphone to your voice rather than the other way around. You should never have to yell. Make sure to point the microphone towards your mouth before you speak.

When using a lectern microphone, adjust by the neck, not by the microphone itself. Try to position the microphone so that it stays eight to ten inches from your mouth. This distance will capture your voice while still allowing you some freedom to move around. Do not move too much, though; move your body, but keep your mouth angled at all times towards the microphone. Only if you are using a handheld microphone should you move more. In that case, take advantage of the portability to move closer to the audience and form a connection with them.

Do not hit or blow into any microphone. Such actions may damage the equipment.

Laser Pointers

Laser pointers, when used correctly, can assist you enormously on the visual aspect of your presentation. You might use them to point out particular data or draw attention to important words and details. However, the technology of laser pointers can pose unique safety risks to users and audience members, so you should choose and control laser pointers with caution.

How Do Laser Pointers Work?

Inside every laser pointer is a rod. On one end of the rod is a flash tube which acts as the source of light. When you press the button, the flash tube lets in light, exciting the atoms within the rod. As an excited atom returns to ground state, it releases a photon, or a particle of light. The photon's wavelength-- its color-- depends on how much energy the atom releases when it relaxes.

When a released photon hits an atom in the same excited state as the first atom, stimulated emission occurs: the photon stimulates the atom so that it releases another photon of the same frequency and direction. The photons bounce back and forth off a pair of mirrors, continuing to stimulate more atoms to release more similar photons. One of the mirrors also lets some of the photons through and out of the pointer. These photons constitute the laser we see.

What to Know for Presenting

Laser pointers are simple to operate and relatively cheap to buy. Because of this, though, you must exercise extra caution in using them for presentations. Do not fall into the trap of assuming that a cheap, intuitive item must be completely safe.

Choosing a Laser Pointer

First, consider using a presentation remote-- these tend to have laser pointers built into them. If you are set on a dedicated laser pointer, you will probably have to choose between three colors: red, green, and blue. Red laser pointers are the cheapest and the weakest as well as the most commonly used. Green pointers are stronger, and blue pointers are stronger still, producing the clearest beam. Consider the range from which you will generally need to present. Buy a more powerful pointer for situations in which you are farther from the screen. For maximum safety, though, you should not use a pointer with a wavelength greater than 680 nm.

Safety

Laser pointers can cause damage to the eyes. Permanent retinal damage is unlikely, but temporary vision impairment is possible. While most pointers are not too hazardous, more dangerous and powerful ones can be imported. You should not purchase a pointer that is not labelled according to FDA regulations. Look for a yellow caution sticker or a black and red danger sticker- if neither is present, the pointer is not properly labelled and should be avoided.

When using the pointer, do not aim it at anyone's eyes or any reflective surface. Also, take care not to look into the beam yourself.