Yet Another Home Theatre Tutorial
by Don Shoemaker
No, this is not about the coming of digital TV and how you will need a converter box in mid February. It’s not about pictures or pixels, plasmas or LCDs, resolution or black levels. Not discussed as frequently would be an equally significant aspect of home theater- the audio. I will briefly break down the parts of the system- their elements and attributes.
All systems whether a combined receiver,separates,or a “theater in a box” (ugh!) contain two or three separate elements- a power amplifier, preamplifier (or control amplifier), and (often) a tuner. The power amplifier is the most basic form of amplifier providing the “horsepower” to drive the loudspeakers. The preamp is basically the control center that does the switching of sources,controls the volume,and allows you to tailor the sound (tone controls,filters,etc.) The tuner if it has one is simply a source (radio).
THE AMPLIFIER
Watts is watts, right? I got 500 RMS which is 1000 WSBL (when struck by lightning). How much power do you really need? Why do the big box stores have $200. 300 watt amps while some of the specialty stores have 100 watt amps costing several thousand? Ever try to start a car with eight flashlight batteries? Twelve volts,right? The batteries are new! Hmmm. The key is current, or amperes. A speaker is typically a resistive and reactive load,and sometimes an 8 ohm speaker can drop as low as two ohms. So how much power do you really need? A good 50 watt amplifier will play louder than a poor 200 watt one will. Believe it or not ,the average listening level is one watt. When I sold audio I would take an amp with power meters (quite common in the early ’80s and I know I’m dating myself),turn the sound up to a reasonably loud level,cover the meters with my hand and ask people how many watts they thought they were listening to. The answers were all over the board but it was usually around one watt. Why do you need more? Each 3db (decibel, a ratio used to measure loudness) increment requires the amplifier to DOUBLE its power. Let’s say you are listening to a moderate volume of 85db with one watt,you would need two watts for 88db,four for 91,eight for 94, 32 for 100,and 128watts for 106db. Music and movies are full of peaks, and that explosion in your favorite movie could have a 25 or 30db peak! A good amplifier will have 3-6 db of headroom, so it may be able to cleanly double its rated power for the few seconds necessary to produce the explosion without distortion. Another clue would be the rated power as the speaker impedance drops. If an amp is 100 watts into 8 ohms and 200 watts into 4 ohms that is generally a good sign. If you look at the rear of many “theater in a box” (gasp!) sets they will actually caution you against using 4 ohm speakers. How much power you need would of course depend on how efficient your speakers are, the size of your room, and how loud you like to listen.You are better off with more power than less ,as “clipping” is what actually damages a speaker. When an amplifier “clips” it runs out of gas and passes a square wave that burns out a speaker. Under powering is more liable to damage than overpowering.
THE PREAMPLIFIER
Basically the controls and switches for the system, it drives the power amp. Typical output is a maximum of about three or four volts. Most theater preamps also contain the processor and are affectionately referred to as “pre-pros”. The processor decodes the various surround modes,the most common from Dolby Laboratories and Digital Theater Systems (DTS). Most of these process in the digital domain, but usually include some analog processing as well , such as Dolby Pro Logic and numerous simulated surround and music modes. The two companies are like Microsoft and Apple competing for the newest and latest big bang. 5.1 became 7.1 became ES became LSMFT. Here again, what is really necessary? For most people 5.1 will be more than adequate. Two front speakers, one center, two rear surrounds and a sub ( the point one in 5.1) are enough speakers for the average room! 7.1 adds two to the sides. The idea here being that the center channel does the dialog, fronts do the bulk of the background and/or music, rears give a sense of ambience and produce special effects, and the sub is used for the LFE or low frequency extension channel (again the point one). Generally,Dolby Digital has been preferred for movies and DTS for music. Another buzz word from a few years back that is pretty much forgotten today is THX. This was not a decoding process but a set of standards created by a man named Tomlinson Holman. Speaker efficiencies, input levels, and equalization that created his ideal sound when “THX certified” components were all used. Many manufacturers jumped on the bandwagon and produced THX certified products. THX stood for Tomlinson Holman’s Experiment. The rights were owned by George Lucas of Star Wars fame. Many movies were also recorded in THX,typically on laser disc.
SPEAKERS
Often thought to be the most important part of the system, they are not. If you do not get as much from the source as possible and amplify it as cleanly as possible without any distortions or colorations ,no speaker can compensate for the loss. They are important, and of course there are a number of options . In Walls (gasp and ugh!) are best for the decor minded. If you just plain don’t want to see them and are outraged by the sight of wires (this is why I have never married).they are the way to go. You will pay about twice as much for half the sound of a good floor stander. Bookshelf speakers are a good compromise, but you will need a good set of stands as ideally you want the tweeters at ear level. Floor standing are the best value as you don’t need stands. Personal taste is the only factor that will come into play assuming all the compatibility issues have been addressed. Tweeters,horns, electrostatics, there are good and bad examples of all. Take some of your favorite music to a place where you can listen undisturbed for a while and pick what you like the best. One that sounds impressive at first may be fatiguing an hour later.
A QUICK NOTE ABOUT WHERE TO BUY
Big box stores come and go for a reason, and if this is something you are serious about you should go to the people who are the experts. Locally Soundworks, Rowe Audio/Video and The Stereo Shop offer the highest level of expertise with combined years of experience in this field. All three offer installation and calibration services as well as a selection of quality products not carried by the big box chains. Although one prominent chain now offers this type of service, they cannot match the level offered by them. They also provide in store atmospheres conducive to evaluation without the interruptions of the carnival like environment.
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