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thanhthanh
28-02-2012, 01:13 PM
Until recently, the best way to watch a movie was to go to a movie theater. The introduction of VCRs made it easy to rent or buy movies and watch them at home, but TVs just didn't compare to movie theaters' huge screens and surround-sound systems.


Not only did TVs have comparatively tiny screens and lower quality speakers (http://electronics.howstuffworks.com/speaker.htm), formatting a movie to fit the screen got rid of a substantial part of the picture.

http://static.howstuffworks.com/gif/home-theater-new2.jpg (http://electronics.howstuffworks.com/enlarge-image.htm?terms=home+theater+systems&page=2)


Will the comfort of home theaters take the place of movie theaters? See more pictures of home theaters (http://electronics.howstuffworks.com/enlarge-image.htm?terms=home+theater+systems&page=2).
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Now, more and more people are turning their ordinary TV rooms into home theaters. This used to involve a projector and a screen, and it was too expensive for most people to afford. But advances in technology have given people more choices for home theater setups, and some people find that a home theater is quieter and more convenient than a movie theater -- and the picture and sound are great.
If you're looking for a home theater system, you have a lot of decisions ahead of you. In this article, we'll go over all the components that make up a home theater system. You'll learn what each component does and what to keep in mind when you make your selection. If you're thinking of turning your den into a fully functioning home theater, this article will help you get started.
What Is Home Theater? Home theater is difficult to define -- it's really just a vague term for a particular approach to home entertainment. Generally speaking, a home theater system is a combination of electronic components designed to recreate the experience of watching a movie in a theater. When you watch a movie on a home theater system, you are more immersed in the experience than when you watch one on an ordinary television (http://www.howstuffworks.com/tv.htm).
To see how home theaters do this, let's take a look at the original model -- the movie theater. When it comes to picture and sound, the theater can offer an amazing experience we just don't get at home. That's usually why people will pay to go to the movies, even though renting a movie is cheaper. There are a few main components that make watching TV and going to the movies very different.


One of the biggest differences is the sound experience. When you go to see a movie in a quality movie theater, you'll hear the music, sound effects and dialogue not just from the screen, but all around you. If you've read How Movie Sound Works (http://www.howstuffworks.com/movie-sound.htm), you know that a standard movie theater has three speakers behind the screen -- one to the right, one to the left and one in the center -- and several other speakers spread out in the rest of the theater. In this surround sound (http://www.howstuffworks.com/surround-sound.htm) system, you hear different parts of the soundtrack coming from different places. When somebody on the left side of the screen says something, you hear it more from the left speaker. And in a movie like "Star Wars," (http://www.howstuffworks.com/framed.htm?parent=home-theater.htm&url=http://www.starwars.com) you hear a rumbling swoosh travel from the front of the theater to the rear as a spaceship flies toward the camera and off the screen. You are more involved in the experience of watching a film because the world of the movie is all around you.

The second chief component of the theater experience is the large size of the movie screen (http://www.howstuffworks.com/movie-screen.htm). In a theater, the screen takes up most of your field of view, which makes it very easy to lose yourself in the movie. After all, you're sitting in the dark with only one thing to look at, and everything you're looking at seems much bigger than life.
We also enjoy going to the movies because we can see everything so well. Film projectors (http://www.howstuffworks.com/movie-projector.htm) present very large, clear pictures. The detail is much sharper than what we see on an ordinary 19-inch television, and the movement is much more fluid. We may not consciously recognize this, but it does make a significant difference in how we enjoy a movie. When we can see more detail, we are more engrossed in the world of the movie.

What Do You Need? In the last section, we saw that the major components of a movie-theater experience are a large, clear picture and a surround-sound system. To build a home theater, then, you need to recreate these elements. At the bare minimum, you need:


A large-screen television (http://www.howstuffworks.com/tv.htm) (at least 27 inches across, measured diagonally) with a clear picture
At least four speakers (http://www.howstuffworks.com/speaker.htm)
Equipment for splitting up the surround-sound signal (http://www.howstuffworks.com/surround-sound.htm) and sending it to the speakers
Something that plays or broadcasts movies in surround sound, preferably with a clear picture

And, of course, you'll need a room where you can arrange all this stuff.
There are any number of ways you can meet these criteria. In the end, your home theater system depends on how much money you're willing to spend and how important certain areas of performance are to you.


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One home theater option is a "home theater in a box" system. This one from Sony consists of a DVD player with built-in surround-sound receiver and a collection of speakers.


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If you're not looking to spend much money and already have a good-sized television and a stereo system, you can upgrade your entertainment system into a fairly crude home theater with a couple of extra speakers and a few other inexpensive components (see Accessing the Surround Channel (http://www.howstuffworks.com/surround-sound5.htm) to find out how). If you invest in a basic surround-sound system and a new DVD player (http://www.howstuffworks.com/dvd.htm), you might spend $500. For a more advanced system, with a larger television and an advanced sound system, you might spend about $8,000. For $30,000, you could set up a real theater, with a projection television (http://www.howstuffworks.com/projection-tv.htm), built-in speakers and bolted theater seats (and maybe a concession stand).
In the following sections, we'll look at the different options for televisions, surround-sound receivers, speakers and video sources. We'll find out the advantages and disadvantages of different types of equipment, as well as the price range and long-term benefits. We'll also look at some of the extra components you can add to put the finishing touches on your home theater system.
Surround Sound Basics The main thing that sets a home theater apart from an ordinary television setup is the surround sound (http://www.howstuffworks.com/surround-sound.htm). For a proper surround-sound system, you need two to three speakers in front of you and two to three speakers to your sides or behind you. The audio signal is split into multiple channels so that different sound information comes out of the various speakers.
The most prominent sounds come out of the front speakers. When someone or something is making noise on the left side of the screen, you hear it more from a speaker to the left of the screen. When something is happening on the right, you hear it more from a speaker to the right of the screen.
The third speaker sits in the center, just under or above the screen. This center speaker is very important because it anchors the sound coming from the left and right speakers -- it plays all the dialogue and front sound effects so that they seem to be coming from the center of your television screen, rather than from the sides.
The speakers behind you fill in various sorts of background noise in the movie -- dogs barking, rushing water, the sound of a plane (http://www.howstuffworks.com/airplane.htm) overhead. They also work with the speakers in front of you to give the sensation of movement -- a sound starts from the front and then moves behind you.
But how do all these sounds get split up? This is the job of the audio/video receiver, which is the real heart of a home theater. In the next section, we'll see what this component does.
The Receiver The audio/video (a/v) receiver and amplifier assembly in a home theater does the same job as the receiver and amplifier assembly in any stereo system: It receives signals from various input devices, like a VCR (http://www.howstuffworks.com/vcr.htm), DVD player (http://www.howstuffworks.com/dvd.htm) or satellite dish. It interprets and amplifies those signals and then sends them to output devices -- your television (http://www.howstuffworks.com/tv.htm) and sound system.


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A surround-sound stereo receiver from Sony



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A home theater a/v receiver and amplifier assembly actually combines several different components. Some even have a DVD or other media player built in. You can generally assemble a superior home theater system by buying the components separately, but most people buy one unit that does all these jobs because it is more cost effective.
The receiver's components are:


Audio/video inputs for video sources (DVD player, DVR)
Preamplifier
Surround-sound decoder (aka signal processor)
Power amplifiers for each sound channel
Outputs for speakers and television

The path of the audio and video is pretty straightforward. The source component (DVD player, DVR, etc.) feeds a signal to the receiver unit. You choose which input component you want to feed to your output unit, and the preamplifier selects this signal and amplifies its line level a little bit.


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The receiver is at the heart of a typical home theater system.


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The receiver sends the video on to your television and sends the audio to the decoder. The decoder sorts out the different sound channels from the video signal, and then sends the information to amplifiers for each sound-channel output. These amplifiers are connected to the appropriate speaker or speakers.
Digital decoders and analog decoders handle the job differently. Digital surround sound is quite simple: When a company is producing a Dolby Digital® program, for example, they encode six separate audio channels, specifically balanced for a Dolby Digital speaker setup. A Dolby Digital surround-sound decoder recognizes these different channels and sends them to the appropriate speakers.
Analog surround sound is something else altogether. The different analog surround-sound channels are actually extracted from the two standard audio channels that make up any ordinary stereo signal. This is commonly called 4-2-4 processing because the encoder essentially takes the rear and front channels and works them into the ordinary stereo channels, and a surround-sound decoder separates the four channels out again. See How Surround Sound Works (http://www.howstuffworks.com/surround-sound.htm) for more information.
There are a wide range of audio/video receivers available. These receivers are often sold with all the speakers you need, as a complete home theater system. These systems run as low as $250 and as high as $2,500.
One of the most important differences between audio/video receiver models is what surround-sound formats they support. In the next section, we'll find out what the different formats are and see what they offer.
Which Surround-sound Format? In the last section, we saw that audio/video receivers decode the surround sound information encoded in video signals and drive the appropriate speakers. Different audio/video receivers are equipped to decode different formats. Today, there are two main sources for home theater surround-sound formats -- Dolby Laboratories and Digital Theater Systems. Dolby Laboratories formats include various versions of Dolby Digital® and Dolby Pro Logic®. Digital Theater Systems has created a range of DTS Digital Theater Sound formats.
Between the two companies, there is a dizzying array of sound options. So here's what you need to know:



DTS encoding uses less compression than Dolby encoding. This means that DTS sound is clearer and sharper.
However, DTS encoding is also less commonly used on DVDs and television broadcasts.
Most DVDs have some Dolby sound options, and some also offer choices for DTS sound.

Fortunately, a lot of a/v receivers support a wide range of Dolby and DTS options. When you're choosing a receiver, you should decide two things: whether you want DTS support and how many speakers you want to use for your surround-sound setup. The most common options are 5.1, 6.1 and 7.1 surround, named for the number of channels. The ".1" indicates a channel for a subwoofer. The subwoofer channel carries low-frequency sound to give a bass boost and create a rumbling effect for certain special effects sounds, such as explosions and trains. These are the typical speaker setups and formats that will support them:


5.1 (5 speakers + subwoofer)
A 5.1 surround-sound setup includes left, center and right front speakers. It also has left and right surround speakers. Dolby Digital, Dolby Pro Logic II and DTS 5.1 will all support this format. DTS 96/24 uses a 5.1 channel format to play audio at the same sampling rate at which it was recorded.



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6.1 (6-7 speakers + subwoofer)
A 6.1 setup takes all the speakers from 5.1 and adds a rear channel. Dolby Digital EX uses this format, splitting the one additional channel into left and right rear speakers. DTS-ES, on the other hand, uses a rear center speaker. DTS Neo:6 can also support a 6-channel format.



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7.1 (7 speakers + subwoofer)
Dolby Pro Logic IIx has separate channels for the left and right rear speakers, rather than splitting one channel and directing it to two speakers.



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The sound system is what really makes a home theater experience complete, but the first thing you'll probably notice when you sit down in front of a theater setup is the television. In the next few sections, we'll see how televisions fit into the home theater.

Standard Direct-view Television The biggest variable in home theater systems is the television (http://www.howstuffworks.com/tv.htm). You can go with a large-screen, direct-view television and spend as little as $300, or you can spring for a front- or rear-projection television, which could cost several thousand dollars. The main factors that determine television price are size and picture resolution.
Direct-view televisions (http://www.howstuffworks.com/tv.htm) are the sets that most of us are familiar with. They have a cathode ray tube (CRT) and a scanning electron gun that paints the picture on a phosphor-coated screen. Good direct-view televisions deliver an excellent picture, but because of the tube technology, they are limited in size. The biggest direct-view television screen you can get these days measures 40 inches diagonally.


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A 32-inch direct-view television from Sony: A direct-view television is certainly adequate for a simpler home theater system.


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This is a pretty big picture, of course, and will work well in a basic home theater setup. You might even be content with a 27-inch model. The general rule for television size is that you want a screen that measures about one-third your distance from the screen (if you sit 9 feet from the screen, a 36-inch television screen would be perfect). These are the guidelines for standard televisions, because if your screen is bigger, or you sit closer, the scan lines that make up the picture will seem fairly large, which translates to a lower resolution. This is inherent in the standard television signal -- it has a set number of vertical lines of resolution -- the number of horizontal lines in one screen -- no matter how big your screen is. High-definition television (http://www.howstuffworks.com/hdtv.htm) (HDTV) has more vertical lines of resolution, so you'll be able to sit closer and still see a clear picture when watching HDTV-formatted video.


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With a 40-inch screen, the Sony Wega is at the upper limit of direct-view televisions.


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When you're shopping for direct-view televisions, pay attention to image contrast. A television with a darker screen will give you a better picture because there will be a stronger contrast between light and dark -- black will actually appear black, rather than gray. You should also look for a television with a flatter screen. If the tube is more curved, the picture will be more distorted and you'll see more glare from other light sources. A perfectly flat screen will usually give you the best picture.
If you need a very large television, you'll probably need a projection television (http://www.howstuffworks.com/projection-tv.htm). In the next couple of sections, we'll see what the standard projection technologies have to offer.
Rear-projection Television If a very large screen size is important to you, look into rear-projection televisions. These sets don't have the same size constraints as direct-view televisions because they don't use the cathode ray tube for the display. Instead, they use a projection screen. There are lots of different types of rear-projection televisions. They include:


Cathode ray tube (CRT) (http://www.howstuffworks.com/tv-buying-guide6.htm), which uses three CRTs, one each for red, green and blue. These can produce a great picture with good contrast but can also be heavy and bulky.
Digital Light Processing (DLP) (http://www.howstuffworks.com/dlp.htm), which uses one or three digital micromirror devices (DMDs) to create all of the pixels that make up the image. DLP sets also create a good picture, but gaps between the micromirrors can produce a screen door effect. Some users also notice a rainbow effect when moving their focus from one part of the screen to another in sets that use only one DMD.
Liquid Crystal Display (LCD) (http://www.howstuffworks.com/lcd.htm), which directs light through liquid crystals and magnifies it for projection. An LCD TV can be lightweight and slim, but it doesn't have a good black level -- the ability to produce a true black, which is important for good detail and contrast.
Liquid Crystal on Silicon (LCoS) (http://www.howstuffworks.com/lcos.htm), which is like a cross between DLP and LCD. LCoS doesn't have the screen door or rainbow effects that DLP can produce. It isn't as common as other display types, and some sets don't have a very good black level.



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A 53-inch widescreen rear-projection television from Sony


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Some rear-projection sets may have a smaller viewing angle than direct view sets. No matter where you sit in front of a direct-view television, the screen maintains the same picture quality. If you look at a rear-projection screen from an extreme angle, the picture may be much darker and you won't be able to see what's happening on the screen. Newer projection sets use high-quality screens that work well from most angles, but older sets may have a fairly narrow viewing area.
If you're looking to buy a rear-projection television, the main things to compare are size, resolution and screen quality. Even a top-notch picture can look muddy on a bad projection screen, so be sure to pay attention to screen material. Darker screens are better because they present an image with better light-and-dark contrast. You should also look for a screen made of glare-resistant material.


(Theo HSW)