Surround speakers - Dolby Pro-Logic Surround speakers - Dolby Digital (AC-3) Subwoofers Speaker Volume Levels
Above diagrams provided courtesy of Crutchfield Corp., copyright 1997

Surround Speakers

Dolby Pro-Logic  

The most misunderstood thing about home theater is the placement of the surround speakers. Most recievers refer to the surround speakers as rear speakers. The term "rear" is a totally inaccurate way to describe the placement of surround speakers. The object of surround speakers is not to make it seem as if sounds come from behind, except rather to create a diffuse soundfield, i.e. you should not be able to tell where the sound form the surround speakers comes. Close your eyes, and give it a test. If you can tell where the sound is coming from, you have your speakers set up incorrectly.
If you are not using dipolar or bipolar speakers, your best bet is to set up your surround speakers so that they are beside you and aiming to bounce off the rear wall behind you. If you do NOT have a wall behind you, then you can set up the speakers so they aim towards the ceiling. In either case you are NOT to aim the speakers directly at your ears.

If you have dipolar or bipolar speakers (speakers designed for surround sound), for optimal performance, the general idea is to mount them on the walls directly beside your seating position (or slightly to the back) about 5-7 feet high on the wall. Specific set-ups will vary from manufacturer to manufacturer. These types of speakers are your best bet for true surround sound.

Dolby Digital (AC-3) 

The advent of Dolby Digital (AC-3) has definitely thrown a monkey wrench into the accepted purpose of surround speakers in Dolby Pro-Logic. Because of the fact that Dolby Digital (AC-3) has 6 discrete sound channels, it is possible for a sound to be placed at a precise point in the plane of the speakers. Pro-Logic, on the other hand, uses matrix-encoding which makes it almost impossible to achieve that effect. Now in order to get that effect in a home theater, monopole speakers will have to be used.

Now the choice is whether or not you want this effect. I think that surround sound was developed to surround people, and not in order to give a larger sound field. The best feeling in the world is to hear someone say "Where did that bird chirp come from?" when watching a Pro-Logic movie. Once it becomes a standard to have full-range monopole speakers in the surround area, the loss of that effect is too much. By having dipole speakers, you will get the general idea of where a certain sound is soming from, but not exactly. Once you are able to tell where is exactly coming from, the belief that you are in and surrounded by the movie, is lost. I would fully support getting dipole speakers over monopoles because, I think the general surround effect is more important than having an exact placement of a sound, and therefore a smaller sound field. Dipoles can benefit very much from the stereo surround concept and display its potential, while still surrounding the viewers with the sounds. After all, in movie theaters designed to handle DTS, SDDS, and Dolby Digital, are there 2 surround speakers, or many more?

However, it all boils down to what you prefer. In general, if you really want to hear sounds jump dramtically and precisely between left and right in the rear, go ahead and get monopoles and set them up so that they point right at your ears. But if you want to still hear jumping (although not as dramtically), dipoles are the best way to go. After all, what fun is watching a Star Trek movie with the hum of the ship soming from one space, and not all around?

Sub-Woofers

Now, is this a sub, or a coffee table?

These are the bass-crunching speakers that frequently are the most costly speakers of a home theater set-up. They are used to reproduce the lowest octaves on the sound scale. The bottom end of the frequency ranges go from 15-60hz, the upper end usually ranges form 60-120hz. In general, the lower, the better. The better subwoofers have an adjustable crossover point (the frequency where the sound siganal is sent to the alternate speakers instead), or even a remote control. most commercial retailer will tell you to stick that puppy into a corner. Although that is a good place to start, it is NOT the best place. If you decide to wedge your sub into a corner, it will only result in a very boomy effect. You should start there, and move the sub away from the wall until you get a smooth seamless sound between the sub and main speakers.
Having two subs is always a considerable option, although maybe not practical. Most home theaters can easily get away with having just one. The main point of having two subs is not for a stereo effect (bass below about 80hz, when accompanied by other higher frequencies is omnidirectional), but rather to get rid of the effects that the shape of the room might have on the bass response. If you got the money, go for it.

Oh yeah, and powered subs are always better than passives subs (unless you have the money to buy an excellent separate amp for the sub). Powered subs relieve the amplifier or reciever from the strain of reproducing the lower octaves.

Speaker Volume Levels

This is one of the most important aspects of home theater, and often, it is often one of the most disregarded. The point of the subject is to set the levels of your speakers so that all of your speakers reach you with the same loudness. Key tools that you will need are a pink noise generator (on all Pro-Logic and Dolby Digital equipment), and your ears or a sound pressure level meter, depending on how accurate you want to be. When using your ears, you should hit the pink noise generator on the reciever (or possibly test tone), and listen to the sound as it goes from speaker to speaker from your listening position. Try to adjust the speaker levels so that the noise form each of the speakers reaches you with the same loudness. In order to be more accurate, a sound pressure level meter is required (about $35 from Radio Shack). Set the volume control on the reciever to normal listening levels, and the switch on the SPLM to C-weighting. Now hit the noise generator. Make sure that for each of the speakers, the needle or display reads the same number. If it doesn't then adjust accordingly. Once they all read the same, you will hear the movie the way the director intended, creating the true soundfield that was so painstakingly created in the sound studio. Your effort will be well rewarded.

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