Most of us here on the earth realm have two ears. There may be other realms with more, but with two we can do amazing things with sound.
Knowing the location of where a sound is coming from is one cool example. You can close your eyes and you can tell whether a sound is coming from the left or right or front center or anywhere in between. In fact, you can close your eyes and point with great accuracy to the location where a sound is coming from anywhere in the space around us, even behind, above and below. The science people call all this space, left and right, above and below, in front, behind – all this is called a ‘sound field’.
In a movie theater, the screen typically shows what is happening – the action and the sceen. But what happens in the sound field – the whole room – is used for more than one purpose. It recreates what is happening in the sound field of the scene in the movie – voices and the sound of water or effects which may not be on the screen at all – and it creates music that usually isn’t happening on the screen.
In that simple sentence, there are many complications. We’ll ignore the fact that an orchestra isn’t hiding somewhere under or behind the screen – even though it may sound like it. But we won’t ignore the fact that the small, enclosed movie theater is being made to sound like an even smaller kitchen or a huge outdoor football stadium. It takes a lot of science and a lot of technology to trick our two sophisticated ears. If you stand in an empty stadium, you will know for certain that you are not in a kitchen. Yet, in a cinema, we are tricked…or as the experts say, “We suspend disbelief.”
Many years ago there was just one channel of sound in the theater, even if it had many speakers. Then stereo came – two different sound sources playing two different sounds – and soon after 3 channels. Three channels really helped fool the ears into thinking that a person walking across the screen was making the sounds at that location. And, most importantly, you will notice that 85% of the sound of voices come from the center front channel speakers.
As our sound systems at home became better, the ability to suspend disbelief was challenged. Many companies worked on many different ideas, and finally we started seeing a standard set up: speakers along both side walls, speakers on the rear wall, and an unknown amount of speakers behind the screen that we don’t see.
In fact, two of the major systems – Dolby and DTS – used Left Front, Center Front, and Right Front speakers. These speakers are far larger than the side and rear speakers that we can see. These main sound speakers behind the screen were also joined with a speaker for Low Frequency Effects. (There was a third company which added to more speakers behind the screen, but it wasn’t as popular and disappeared, so we won’t go into its details.)
We use the term ‘speakers’ when we usually mean ‘speaker cabinets’. In most speaker cabinets there are several speakers. There are many reasons for this, and maybe we will discover that in a future lesson. But what we know is that speakers are like everything else in the audio and picture chain – simple in looks, but with as many potential points of failure as there are potential points of excellence.
The man who wrote the book 2001: A Space Odyssey, Arther C. Clarke, had a set of Laws. The 3rd one is: Any sufficiently advanced technology is indistinguishable from magic. Without damaging the magic, let’s look some more into these speaker systems.
To separate the different kinds of systems, we have to remember our lessons in frequency. A speaker that handles the sounds of a screeching hawk is handling high frequencies. The roar of waves is duplicated by low frequency speakers. Handling the human voice is for mid-frequency speakers.
Oh, yes. We also have to remember that saying: Engineering is the Art of Compromise. A small cinema cannot afford to purchase and install the very best audio systems in all their rooms and make enough money from customers to keep it sounding great. We have to compromise somewhere in every project. With speakers that means more or less volume, or more or less accuracy. Accuracy means more or less distortion, or better or worse placement of sound in the soundfield.
If I play speakers too loud, the amount of distortion increases. If I constantly play speakers too loud, they will lose their ability to play accurately more quickly. The answer is to make a system that has more speakers, so they can be played less loud. So that is one of many reasons that the left front may be made from a combination of speakers. And, all the other speakers – even the ones you see on the side probably have two speakers inside.
The purpose of this lesson is to describe the basic different sound systems of a typical cinema theater. We want to be able to have a clear enough understanding that we can help customers describe what they hear when they tell you about a problem, and to help describe problems to the technician who has to repair problems that we discover.
Be aware that home and theater sound system may use the same terms, like seven point one (7.1) or five point one (5.1). But there are differences in how they work, how they handle the sound. So don’t be confused if you run across information on the web that says two different things. They may use the same term but use it in a different way.
Remember also that all systems are part of a continuing evolution in the attempt to deliver a sound in the theater that is as close as possible to what the director wanted to create. Again, the Director’s Intent – the idea that the director can create an effect in the audience with a particular combination of sights and sounds that deliver the story. Before there was sound recording, the director may have specified the music for a piano or organ or orchestra to play with the movie, then the the ‘talkies’ were delivered with a single track of sound for one speaker. We call that mono.
Then, a lot later, two tracks of sound for two separate speakers – Stereo.
The evolution gets complicated after that.
So, guess what is next in the Series?!? Part II of Point 1…