To make it sound as though Han Solo is dodging not only the asteroids onscreen but your living room furniture as well, you'll need a "Surround Sound" home theatre system.
But before you go charging off to the store, let's take a moment to understand just how it is that surround sound makes you want to peek behind the couch to check for swooping TIE fighters.
How you hear
Quick refresher on what hearing is all about: Sound is created when an object vibrates, causing the air particles around it to move. These vibrating particles influence neighboring particles, creating a cascade effect commonly known as a sound wave. Our eardrums -- pieces of thin, taut skin located deep inside our ears -- are extremely sensitive to these waves, detecting and translating even the smallest air vibrations into neural stimuli that our brains interpret as sound. The brain can tell the direction from which sound waves emanate.It's easy enough to understand how it distinguishes sounds coming from your left or right; after all, your ears are positioned on either side of your skull. They can sense split-second discrepancies in the amount of time a sound wave takes to reach each eardrum and are also capable of discerning subtle differences in volume. But how sounds coming from in front, behind, above, or below are accurately perceived is a little more complicated -- and way cool. Turns out, timing and amplitude play a key role, as does all of that squiggly tubular stuff leading into our ears that we call cartilage. As sound bounces off the various bits of your outer and inner ear a pattern is created in the wave that helps the brain recognize it as stemming from a particular direction.
The science of how we hear is pretty clear (ha ha), but that science can also be manipulated so as to alter our perception of sound. This field of research is called psychoacoustics, and there are psychoacoustic technologists who spend their days dreaming up new ways to make our brains believe that sounds are coming at us from the four corners of our living rooms -- sometimes with as few as just two speakers.
True Surround Sound = speakers all over the place
True surround systems go easy on psychoacoustic trickery. If you hear the sound of a truck idling behind you, it's probably because there are a couple of speakers back there rumbling away. And if you seem to hear that truck start to drive off to the right, then turn and zoom across the floor in front of you, it's likely because the soundtrack you're listening to is cleverly building up the volume of the truck's engine in one speaker out in front while fading it down in that speaker behind you, and sometimes repeating the process for the various speakers scattered throughout the room to cause a gradual shift in the direction and timing of the sound waves reaching your ears.
Consumer surround sound systems come in a variety of configurations. The most basic, known as 3.0, has been around for about a quarter of a century and is composed of three speakers (hence the 3.nothing-else nomenclature) placed front left, front right, and rear. The old fashion "stereo" would today be called a 2.0 system (the headphones for your iPod can also be considered "2.0") while adding a subwoofer to that -- as in your modern desktop computer with an external speaker system -- and you've got 2.1, which is not surround sound, just stereo with a fat bass kicker. Just so you know.
Of course the more speakers, the greater the potential for more realistic surround sound. Modern high-end systems employ as many as seven distinct channels in a so-called 7.1 configuration that involves speakers placed front center (usually reserved for dialog), front left, front right, left, right, rear left, and rear right. The ".1" refers to an eighth channel delivered through a subwoofer, which outputs extremely low frequencies (aka "bottom end" or "bass") that other speakers in the system are incapable of generating as their speakers are too small and their magnetic "driver" too wimpy to push (or woof) enough air at a slow enough rate. (Note: the subwoofer is not used for directional audio trickery; it pumps out a mono signal to simply provide an overall, augmentative "oomph" to the regular directional audio, which is why it's only classed as .1 and not dedicated "1." speaker unto itself.) However, in order to take full advantage an 8-channel (7.1) speaker system you need to have an 8-channel audio source, which is rare.
Most major movies on DVD today are encoded in Dolby Digital 5.1 surround sound, which means that sound designers encoded the film's audio using a surround standard created by Dolby Laboratories that employs five distinct channels, plus the low frequency mono channel. Though lacking the two, mid-room left and right channels of a 7.1 system, 5.1 soundtracks, nonetheless, expertly engineered to be distributed across all of the channels to make the sum-total audio follow and flatter the onscreen action. A movie played through a speaker system designed to decode a Dolby Digital 5.1 source, as most modern surround systems are, the soundtrack has the potential to sound exactly as the filmmakers intended.To achieve true 7.1 surround you'll need not only a system designed to decode a 7.1 encoded digital signal, but also source content encoded with eight discrete audio channels. Thanks to the emergence of the new high definition audio/video optical formats Blu-ray and HD DVD, which support the 7.1 standard, movie companies now have a means to deliver films in true 7.1 surround sound. The trick is finding a Blu-ray or HD DVD that has actually been encoded in 7.1 -- studios have yet to embrace this new surround standard.
Virtual Surround Sound = fewer speakers, same result (more or less)
While true surround sound delivers a highly realistic audio experience, many people don't want to go through the hassle of running speaker wires throughout their living rooms. That's where virtual surround sound comes in. Virtual surround systems involve a little more psychoacoustic ingenuity since they strive to create a surround sound experience using only speakers that are positioned directly in front of the listener. Given what we've learned about how sound and our perception of it works, this might seem a bit far-fetched, but the science is sound (ha ha again) -- so long as the listening environment is configured within precise parameters.
The most common kind of virtual surround sound systems use room walls as reflectors. The sound wave begins its life emanating from a speaker heading toward a side wall in the room. Then, to simulate a rear speaker, the sound is deflected at a shallow angle backwards toward the room's rear wall, where it then bounces once more towards the centre of the room. When the apex of the sound wave finally reaches the listener's ear, it is, in fact, coming from behind, creating the illusion that it originated from the rear. To mimic side speakers the wave bounces off the side wall at a sharper angle so that it arrives at the centre of the room before hitting any other walls.The problem with the bouncing method is that its success is largely dependent on room symmetry. A wall protrusion or tall piece of furniture could interfere with the paths of reflecting sound waves. Certain surfaces, like sound absorbing curtains, also tend to have an adverse effect on sound reflection.
Philips Ambisound SoundBar
A potentially more successful method of achieving reliable virtual surround is to make sound waves bend around the listener. Or at least appear to. This approach involves some hardcore psychoacoustics, and companies that have researched such highly sophisticated systems are understandably hesitant to give up their secrets. Suffice to say these virtual surround setups use complex digital algorithms to tamper with the sound wave. By adjusting properties of the wave a sound can be created that, say, carries with it the pattern of a sound originating from a different direction, or a property that effectively cancels out certain sounds not meant to be heard by one or both ears.
Philips' virtual surround SoundBar is an example of applied psychoacoustics. By tampering with specific sound wave properties, the unit can make certain channels appear to bend behind a listener without reflecting off of any walls.
For a clearer explanation, we went to Philips to see if they could explain their new Ambisound SoundBar system, which employs some serious wave processing along with creative placement of six speakers in a single bar less than a metre across. Alas, a 20 minute discussion with a Philips engineer did little to shed additional light on the Ambisound enigma -- there was talk of "notches of silence" directly in front of the listener in which certain sound waves were simply "absent" (see illustration), but just how it creates these notches and bends sound is something of a proprietary mystery. However, if the awards won by the SoundBar at this year's Consumer Electronics Show in Las Vegas are any indicator, there seems to be method to Philips' psychoacoustic madness.
Better with than without
Virtual surround sound can be kind of trippy and a little disconcerting, but in the right kind of home theatre environment and with a properly positioned audience, these systems can be astonishingly effective.
However, if you want the most authentic surround experience (and are willing to put some time and effort into wiring and positioning several speakers), a system involving six or more discrete channels is still your best bet.
If all this technical gobbledygook isn't your cup of tea, just place your trust in the audio engineers that wrote the manual for the system you buy despite your technical ineptitude and just follow the setup instructions. The first time you flinch away from the sound of an explosion coming from behind your couch, you'll realize that not only did you do it right, but that it was worth the effort.
