In November of 1940, a process called “Fantasound” created a stereo sound track for the Disney movie, “Fantasia”.
At its debut in New York it was hailed as a technical marvel, but it didn’t catch on, partly because of the renovations required of theatres to make it work.
It wasn’t until 1952, when Cinerama was being hailed as a great step forward in the movie experience, that stereo soundtracks were more widely used in theatres.
In the 1990’s innovations in sound processing tumbled over each other to provide more realistic movie sound. By that time home theatres were already beginning to appear, built around large rear-projection televisions, laser-discs and Dolby Pro-Logic surround sound. Pro-Logic is a system that takes two audio channels and uses “psycho-acoustics” to create the illusion of surround sound.
Eventually the ability to record and playback several discrete audio channels became the norm for movies and along with high-def television displays that set the stage for amazing movie experiences in a home theatre.
Now it’s possible to buy, at pretty low prices, a “home theatre in a box”, so that you can enjoy true surround sound without spending a fortune. Of course, you can spend a lot more and the advantages of the higher price tag are immediately apparent when you sit down to watch a movie. But whether your system is at the low or high end of the price scale, there are things you can do to make sure that you are getting the most out of it.
First it helps to understand how multi-channel soundtracks are designed to work and what the terms mean. You’ll find that DVD’s are available in Dolby Digital or DTS surround. These are competing companies that encode the multiple channels.
As with anything in audio, you’ll find a lot of debate about which is better, but it’s difficult for the average listener to tell the difference. All you really need to do is check to see that both can be handled by your equipment. If it handles just one, you’ll have to look for DVD’s with that encoding. The most common multi-track setup is called 5.1. It consists of three front speakers and two rear speakers plus an LFE (Low Frequency Effects) channel which is fed separately to a powered sub-woofer. A 7.1 system is the same with two additional channels added at the sides of the room. The creators of the movie have decided which sounds to send to each channel. To obtain the effect they had in mind you will want to take care with the positioning and balancing of your speakers.
The size and shape of the room will affect how the surround sound works for you. The ideal shape is rectangular and enclosed, a room with the same proportions as a shoe box. Of course, that’s the ideal, but it’s not always possible. If your theatre is part of a family room or rec room that opens on to another area, the sound on that side has nothing to bounce off and so you may have to adjust the setup. All speakers should be from the same manufacturer to avoid differences in timbre as the sounds move from one speaker to another.
With a “theatre-in-a-box” this will be the case but if you are setting up something more expensive, there is a wide choice of speaker sets specifically designed by manufacturers to work together for surround sound. Speakers with widely differing sonic qualities can destroy the illusion the film maker was trying to create.
The acoustic qualities of the room can affect the sound as well. Hard reflective surfaces will emphasize the high frequencies while soft surfaces will absorb them. The easiest way to adjust for the acoustic properties of the room is to use an equalizer, like the ones people used to feed their stereos through, to counteract what the room does to the sound.
The three front speakers must relate to the screen. The centre speaker carries the dialogue and it is best situated directly above or below the screen. The left and right front channels set up a stereo sound-stage, which is the illusion of an aural space. Treat them as you would stereo speakers, spread no more than eight feet apart on each side of the screen, at approximately listening level if possible. You may find it improves the sound to aim these two speakers directly at the listening position.
The two rear speakers carry ambient sound. If you notice the sound coming from the speakers behind you it distracts from what you’re watching. It’s better to hear the ambient sounds coming from all around. To achieve that with a pair of rear speakers, aim them at the wall or ceiling instead of at the listening area. That way they are diffused and more difficult to specifically locate.
If one wall is missing, as noted above, it makes more sense to aim the rear speaker in the general area of the listening position because there’s nothing for it to bounce off. If it is a 7.1 system, you can point both the side and the rear speakers at the listening position and the extra speakers will give a greater sense of being surrounded by sound, without drawing your attention to particular speakers. The side speakers should be at head level when you are seated watching a movie and they work better if they are dipole speakers, sending sound in two directions at once.
Often people will install recessed ceiling speakers, three across the front above the screen and two at the back of the room. These work well to create an encompassing surround sound, particularly if they have swivelling tweeters that can be aimed. The tweeters of the three front speakers can be aimed at the listening position while the rears are aimed at the back wall.
The distance between the listener and each speaker is critical to getting the right effect. With a “theatre in a box” the closer you can come to putting each speaker equidistant from the listening spot the better results you’ll get.
More expensive setups with an Audio-Video Receiver allow each speaker to be individually adjusted according to its position. In some cases you set up the speakers by entering into the receiver the distance between each speaker and the listening post. Other receivers generate a “pink noise” tone that you can measure through each speaker with a sound level meter located at the listening spot so that they are all at the same level.
Still other, more expensive, receivers come with a microphone and built-in software that automatically calculates the right level for each speaker. The goal is to hear the same level of sound from each speaker when you are sitting in the viewing area so that the variations created by the movie maker will be reproduced accurately.
The sub-woofer can be placed anywhere in the room because it is difficult for the ear to locate the source of low frequency sounds. It is usually recommended that it be set in a corner, which augments the bass effect and prevents standing waves from nullifying it. The sub can be individually adjusted to suit your preferences. For some people the boom and rumble from the sub is the most exciting thing about a surround sound movie. If you’re one of them, you may even want to add a second sub to enhance that effect.
Surround sound has now become an integral part of movie making and without it you are missing part of what the director intended you to experience. With these basic guidelines, the performance of a surround sound system in any price range will be enhanced, adding to your viewing pleasure.
Bill Monahan is a “smart home” specialist who has been in the construction industry for thirty years, with the last twelve devoted exclusively to residential electronics. While he provides and installs products he sees his main mission as making homeowners comfortable with the new technologies.
