The physical positioning of speakers is key to creating mixes that translate well to other surround playback systems. As the 5.1 format is the most widely used, this section will only cover 5.1 speaker placement. Much of this information can be applied to the other formats.
The International Telecommunications Union (ITU) created a 5.1 definition that states that the front speakers should be arranged left, center, and right, with the angle between the left (or right) and center speakers being 30 degrees.
A narrower angle of 22.5 degrees has been suggested for use in cinematic systems to comply with another requirement that the left and right speakers should be within four degrees of the edge of the screen.
The ITU standard is primarily aimed at music-only systems, but you should consider using the wider 30 degree angle, even if scoring for film. Use of this angle also allows stereo signals to be auditioned correctly using just the left and right speakers, without resorting to moving them around each time you switch between stereo and surround jobs in the studio.
The three front speakers—left, center and right—should be placed in an arc (not a straight line) at an equal distance from your listening position. In other words, the center speaker should be set back slightly from an imaginary line drawn between the left and right speakers. If this isn’t possible, ensure that you don’t place the center speaker closer to the listening position than the left and right speakers.
If possible, your listening environment should also include a spot where the left and right speakers are at an angle of 45 to 60 degrees from the ideal central “viewing” position.
An angle nearer to 45 degrees is preferred if watching movies, as it approximates the circumstances in which film soundtracks are mixed and monitored. A wider angle, with the left and right speakers farther apart, is recommended if you generally use your system for listening to music, rather than watching movies.
This doesn’t have to be in the studio. If you’ve got a home theater setup, make your surround mix in the studio, and listen to it/watch the DVD in your theater room (which presumably has all speakers in “ideal” positions for film viewing).
The three front speakers should be as close as possible to the same height, at or near ear level. Because it is often easiest to place the center speaker on top of the TV set at a fixed height, consider mounting the left and right speakers on adjustable stands so that you can match their height to that of the center speaker.
The rear speakers (surround channels) should ideally be placed at the same distance from your listening position as the front speakers, at an angle of around 110 degrees from the front center speaker. This angle is a compromise between producing an all-encompassing sound stage (at 90 degrees) and the best rear-quadrant imaging (at 135 degrees).
The surround speakers should be placed alongside and slightly to the rear of (but not behind) the listening position, well above ear level, to help minimize localization effects. They should be aimed across the listening area, not directly at the listening position.
This positioning creates a broad surround sound field throughout the listening area, which approximates cinema speaker systems. If the speakers are placed too far forward, you won’t get sufficient rearward effect, and if the speakers are too far back, the surround information will not be integrated with the overall sound field.
Your studio may not have walls in the perfect place to mount surround speakers. If this is your situation, try these options:
If you’re in a rented space, place the surround speakers on stands above ear level.
Generally, placing surround speakers on the wall directly behind the listening position is not ideal. If you have no other choices, mount them well above ear level, and try aiming them at each other, toward the front, or to reflect off the side walls.
You can also try placing them to the sides or rear aimed upward, either on the floor, or a couple of feet off the floor.
Experiment with placing and aiming the speakers until the surround sound field seems to “wrap around” you, rather than seeming to come from behind you.
If you mix “traditionally,” by sending the bandwidth-limited LFE signal (all frequencies below 120 Hz from all channels) to a subwoofer in your surround speaker setup, you don’t need to concern yourself too much with its placement.
Bass frequencies travel much slower than higher frequencies, and aren’t very “directional,” so placing the subwoofer under the desk or to the left or right of the room (but in front of the listening position) will be fine.
You may or may not have wondered why the front speakers are ideally arranged in an arc, why the subwoofer positioning isn’t too important, and why specific angles are better than others for surround speakers.
The reason, put simply, is due to the way human beings “hear.” Most people with undamaged hearing can easily identify where a sound is coming from: to the left, right, in front, or behind them.
Certain sounds, however, are very difficult to “position,” in relation to the listening position. For example:
A gunshot or car backfiring: These are hard to place because the sound is both loud and quick. You may initially be able to tell that it came from your left or right, but your brain will become confused as to where, specifically, to the left or right it came from. This is because early reflections (reverberations) rapidly build up and diffuse, making them hard to discern, directionally, from the initial sound peak.
Aircraft jet engines: In general, this is just a low rumble that is hard to place, until the plane flies directly overhead. When it does, the sheer volume of the sound, and the higher frequencies of the jet engines enable you to hear it moving from left to right or front to back.
Sounds that are easier to place include:
Trucks, cars and motorbikes: As these move, a constant combination of low- and high-frequency sound is heard, allowing you to track their movement.
Human voices: This is the sound that human beings are most familiar with, and contain a lot of high-frequency content. Interestingly, grouped human voices, such as a crowd in a sporting stadium become very nondirectional. This is due to the reflections and reverberation of the arena.
As an individual creating a sound mix, you can try to approximate the “real-world” characteristics of certain sounds, or artificially enhance them, as heard in many Hollywood blockbuster films.
Whichever approach is taken, a certain amount of “lag time” (latency) is perceived between speakers, in relation to the listening position.
To compensate for this perceived lag time, most surround amplifiers offer a calibration routine that allows you to set different levels and different delay times for each speaker.
Care must be taken with this, as level—in particular—can alter your perception of how “close” a sound is, so you should ideally set the same level for the left and right speakers. The front left and right speakers are usually used for “incidental music/effects” tracks and the “main score,” and also often carry an amount of the “dialogue” track (at a slightly lower level than the center speaker). They may also be used for “surround effects,” such as crowd noise or ambience in a scene where the main actors are in the center of a group of people.
The center speaker is usually used for “dialogue,” and “incidental music/effects,” tracks in films. Its level should be fairly close to that of the left and right speakers, but can be increased a little to enhance the intelligibility of dialogue.
In general, you should aim to have the sound from all front speakers arriving “evenly” at the listening position at the same time.
The level of surround speakers and the subwoofer (LFE) is also critical. You want to set these levels to be “immersive,” and part of the surround stage, rather than “additions” to the front speakers. In general, surround speakers are used for “surround effects,” “main score” and “incidental music/effects” tracks.
Also critical for the surround and subwoofer channels is the delay time. Unfortunately, there’s no formula that will work for every listening situation, due to a range of factors, such as surround speaker distance from the listening position, among others.
Assuming that the levels of all speakers are suitable, the timing of the surround (and LFE) speakers may seem slightly “out” in comparison to the front speakers. Most surround amplifiers allow you to negatively or positively adjust the “delay” of these speakers.
When mixing in Logic Pro, you should aim to strike the right balance between all of the factors discussed.
The surround encoding process—performed in Compressor—writes “surround encode flags” for the surround speakers, depending on the chosen format. These “flags” are understood by surround decoders (AV receivers, decoding software or surround amplifiers).
There’s no need to worry about setting slight delays between tracks when working in Logic Pro. The surround encode flags are designed to handle this.