Broadly speaking the difference comes down to image quality when reproducing full motion picture film. Home theatre projectors are designed from the ground up to perform their best when they are being fed a motion picture image in a darkened environment. Multimedia projectors are usually designed to perform their best under normal lighting conditions with a PC input.
Multimedia projectors often have higher resolution than home theatre projectors - making it easier to read fine text, but the response speed, the colour rendition, contrast ratio and brightness all generally fall in favour of the home theatre projector. A stockhorse and a thoroughbred are both horses, but they have very different uses and requirements.
There is probably nothing more confusing than the aspect ratios 4:3 versus 16:9 for projectors and screens. Video comes in many different aspect ratio formats. Material made for regular TV is 4:3 (1.33 / 4 divided by 3 = 1.33), HDTV broadcast is 16:9 (1.78 / 16 divided by 9 = 1.78), movies, music videos, and other content on DVD comes in a variety of formats like 1.33, 1.78, 1.85, 2.00, 2.35, 2.4, 2.5 etc. There is no universal standard for the shape of a video picture.
For general use, there is no perfect solution and both have limitations for which one must compromise
How many ANSI Lumens are required?
ANSI Lumen = needed Lux on Screen (lux) * Screen Area (m2) / Screen Gain
Example: in a room with regular light (board room or conference room) 400 lux are needed on screen, for a dark room 100 lux are needed.
Acronym for American National Standards Institute, ANSI has established the standards for measuring lumen brightness of projectors.
The ANSI lumen standards ANSI/NAPM IT7.228-1997 and ANSI/PIMA IT7.227-1998 actually were retired on July 25, 2003.
The IEC lumen standard for projectors equals the ANSI standard, but manufacturer hesitate to use a different term than ANSI. The parameter ANSI lumen became too important and the term 'IEC lumen' would confuse the entire projection business. Probably something like "ANSI/IEC lumens" will emerge during the next few years (ANSI and IEC suggest referring to the IEC standards for testing from now on) ...
The IEC lumen standards are IEC 61947-1 and IEC 61947-2, the testing procedures are basically the same as under ANSI: An IEC lumen is the same as an ANSI lumen!
Lumen is the unit of illumination on a surface. One lumen is the light of one candle power on each square foot of a surface of a sphere at a radius of one foot from the light source.
ANSI or IEC Lumens are not comparable to 'lumens' expressed in general lighting terms.
The spatial resolution of a plasma panel, projector or LCD display is measure by the number of pixels (picture elements - dots of colour). This is given as a figure like 853x480 or 1280x720 and describes the actual number of discrete pixels horizontally x vertically.
As a general rule of thumb - the higher the resolution the better, and the longer it will stay current with the existing and next-gen High Definition DVD players and Digital TV broadcasts.
Any device with a vertical resolution of about 576 lines or less is known as a Standard Definition display device. Anything higher is obviously therefore a High Definition device. This is to say a 720p (720 line vertical resolution progressive signal) from a Digital STB displayed on a Standard Def would down-convert the information to the lower resolution of the panel. Send the same signal to a HD panel display and hey presto - you have all the additional detail that was broadcast.
Conversely, sending a Standard Def (or worse - analog TV) to a HD panel display does not mean necessarily a better picture. The quality of the image will depend upon the quality of the video scaler used in the display device.
Nothing too complicated here, this is simply a question of "How black are the blacks and how bright are the whites". Normally the black areas on screen are created by either turning off the pixel (in the case of plasma) or by blocking the light from passing through the pixel (in the case with LCD). Well might you imagine that the absence of glow from a plasma is darker than a bright light being blocked by a thin liquid crystal. Some panels use gloss black lines on the walls between pixels to increase the apparent "blackness" of an off pixel.
Depending on the colour depth of the device, there is also a difference in the number of "steps" between white and black. The greater the colour depth, the more steps, therefore the more subtlety in contrast is available.
It's also worth noting that contrast for front projection depends entirely on the amount of ambient light in the room. Using brighter projectors will never render proper blacks in a daylight or otherwise lit environment. This is why home theatre projection should always be set up in a room that can be properly blacked out.
The Four-Six-Eight Rule -468-
The standard rule of thumb for sizing images is the four-six-eight rule -468-. The farthest viewer should be no more than four, six or eight times the image height away from the screen. Which of the three options depends on the following:
- four times is for material with fine details like CAD drawings or other detailed graphics
- six times is for detailed reading (spreadsheets or text with images)
- eight times is for watching a movie or images
The minimum distance from the projection screen to the first row of seating should be at least 2 times the width of the image size.
The bottom of the screen should be at least 40" to 48" (about 1.2 Meters) above the audience floor, allowing those seated in the rear of the audience to see the screen.
This works for all video aspect ratios: 1.77:1 (16:9) / 1.85:1 / 2.1:1 / 2.35:1.
Screen center should be no more than 20° above the eye level of any viewer.
Diagonal Screen Size:
Because the aspect ratio for video is 4:3, the diagonal produced from those numbers turns out to form a perfect integer relationship: 3 - 4 - 5.
For instance: How large is a 100 inch (diagonal) video screen?
Dividing 100 by 5 equals 20. This multiplied by 3 equals the height of the screen = 60 inch.
Multiply the same 20 by 4 and we get the screen width = 80 inch.
To use a mirror for a rear projection, it must be front-surfaced. Regular glass mirrors have their reflective surface at the back of the glass material. Using this kind of mirror will create double pictures, because the in-beam and the out-beam are not parallel. The light has to go through the glass twice and on the first surface a second reflection will occur.
Front-surface mirrors for projections can be glass and foil mirrors.
Glass mirrors have a reflectivity of about 90% to 95% and foil mirrors have a reflectivity of about 80% to 85%. The glass mirror is perfectly flat but heavy. It can even bend under its own weight. The foil mirror is much, much lighter, can be angled in any way but has not this perfect surface.
Most manufacturers now post projection calculators on their websites.
One of the best and most comprehensive we have found is on the website of Projector Central
Link: - Projector Central's Projection Calculator
These calculators can tell you the maximum size diagonal your screen can be given the projection distance and zoom capabilities of your projector.
Ideally the projector should be place somewhere where any fan noise or light spill will not effect the enjoyment of the movie. Usually this at the very back of the room, although extremely short throw projectors are available as special models or replacement lens kits for some products on the market. Audio Junction staff would be delighted to assist you if you have a requirement like this due to extremely short throw distance needs. One feature of these short throw projectors is that they can bring very big screens to the sides of the rooms rather than always at the end of a long room.
With so many different manufacturers and products available, knowing which screen best suits the projector and room is a bit of an art form.
The first choice should always be a decision on how the screen should be mounted. That includes fixed frame mounting to a wall, or a drop down screen mounted to a wall or ceiling.
Next you should choose a material with the correct gain for the style of projector you plan to use.
Finally Aspect ratio you want the screen to be in. Typical aspects are 4:3 and 16:9. The former is commonly used for multimedia presentations, while the latter is better suited to DVD movies and widescreen digital TV and the next generation of HD wide screen games consoles.
The decision on motorised or not for a drop down screen can normally be left to last as most manufacturers have the same models available with and without motors.
Other options include micro perforated screens that are sonically transparent so that centre speakers can be placed behind the screen firing through.
A fixed frame screen is the ultimate home theatre screen. The biggest advantage to this style of screen is that it never sags or wrinkles, it doesn't sway when the air conditioning is on, and it's always ready for use.
The drop down screen is ideal for apartments or smaller shared lounge theatres. Many people who have large picture windows during the day, at night close the blinds and curtains and bring down the projector screen - transforming the room into a cinema.
The choice of motorised or manual screen is a straightforward one when you weigh up what is most important to you. Manual screens are cheaper. They require you to get up to bring the screen down. Chain drive screens are best so as not to pull the screen from any single point. This will eventually cause stretch ripples in the screen material.
Motorised screens are fairly simple to integrate into a control system, they can be triggered by the projector turning on and off. They are more expensive and more complicated than a manual screen.
The material coating the surface of the screen has reflective properties. The reflectivity of the screen is known as the screen's Gain.
The amount by which a reflective screen (or surface of some sort) reflects light hitting it. A matte white screen has a gain of 1. Higher levels of gain send back more light while lower levels of gain send back less light. A high gain screen makes an image projected onto a screen more easily visible in bright light conditions; however, high gain screens may alter the color to some extent. Most projection screens have gains of 1 or slightly more.
For home theatre use matched to most DLP projectors a screen gain of 1.1 is recommended. Many cheaper screens on the market offer higher screen gains. They always demonstrate them showing animation DVD's where there aren't any true skin tones or reference colours. The overly bright colours really pop off the screen in "Shrek" on a 1.3 gain screen, but put on "Cold Mountain" and it looks more like "Willy Wonka"
Display devices usually have multiple inputs. These can be of any of the basic Scart, composite, component, RGB, DVI, HDMI types of inputs, but the positioning of the inputs may become an issue for installation and ease of control.
Some high end projectors come with an external media box connected to the projector using just one cable (usually requiring a digital HDMI or DVI linkage from the media box to the projector. Optical cable in the case of SIM2). This simplifies the cabling from source and switching devices to the projector's media box In this way source media devices can plug into the media box conveniently located near the rest of the home entertainment equipment. More commonly though all the video inputs are directly on the back of the projector. Composite, S Video, Component RGB DVI HDMI are all frequent acne on the back panels of projectors. Some manufacturers use adaptor plugs to convert from one input to another, this has a disadvantage of limiting the number and type of sources that can be directly connected to the projector.
Composite is the lowest standard of video connection. Normally this is a yellow RCA plug.
S-Video is the next higher quality video connection having much greater bandwidth with the additional conductor cores. S-Video separates colour from brightness and contrast.
Component Video is the highest standard of consumer analog video connection, containing a much greater bandwidth again than S-video, this schema separates colours into Red Green and Blue, much the same way as your eyes do.
As discussed elsewhere in the articles pages, SCART connectors contain all the necessary bi-directional wiring (SCART-SCART cables) to carry left and right audio, composite, S-Video, RGB and control signals. It was designed to be a simple modular system. Also known as the Euro connector for it's prevalence in European devices and markets.
DVI appears to be an interim standard until HDMI really gets off the ground.
HDMI is an all digital end-to-end cable that is designed with security in mind not just quality. It will eventually be the ONLY way to get true high and ultra high definition digital video from the next generation of HD devices. These are modular plug cables and much more difficult to route easily through walls in existing houses.
For projectors Audio Junction strongly recommends the use of broadcast quality Canare cables. These are 5 or 6 core multistranded video hoses. The rubberised outer has a diameter of about 1.6 -2 cm. These multi core cables carry all the conductors to the projector in one cable, simplifying installation immensely as well as improving picture quality and reducing interference.
Special termination tools are required to fir the f-connector or RCA plugs to the ends. This type of cable gives consistently the best results for installation of projectors.
Audio Junction carries a number of different bracket designs in stock at almost all times. Differences between products are not limited to styling and colour, but also on drop height from ceiling, plate mounting, quick release mounts, wall mounting brackets and cable hiding brackets.
During the installation of the projector and the alignment with the screen, the use of some of the setup DVD's available will really speed up the process.
Some of the features on these DVD's include test patters showing borders to align edges and corners of the screen, parallel lines and right angles to ensure the projected image is square and flat. Also colour swatches to are extremely useful for calibrating colour.