Home theater sound
By Roy Johnson, loudspeaker designer, Green Mountain Audio, Inc.
It is possible to adjust your speakers' positions to create surreal surround-sound experiences with every movie. Some report the most fun was realizing they were no longer at home! What really happens is the soundtrack merges completely with the cinematography -- it is no longer a separate perception. This changes your experience, even with a familiar favorite. After all, is that not what home theater is all about? We show you how to leave home without leaving home.
The diagram here shows the usual layout recommended for your five speakers, in gray. Our recommended positions are overlaid in green. We are expecting you to use 'direct-radiating' speakers for your two surround speakers in this diagram, not the type designed to bounce their sound off the walls. More on this later.
Notice first that we bring the two surround speakers in front of the listeners by 5-10 degrees, toed-in to look directly at them. Place these speakers below ear level, tilted up to you.
Second, we spread the two main front speakers apart and toe them in according to our 'Equal-Legged T' layout (more on this below).
Two other adjustments are required.
1) Keep those two main speakers away from any surfaces by at least 36" (1m).
2) Adjust the time delay settings of your control center to make the center-channel speaker and two surround speakers as far away (acoustically) from you as the two main speakers.
When the surround speakers are behind you, you always hear your room's side walls talking back to you. Therefore, you are acoustically still at home. With the surround speakers slightly in front of you, then the left and right sidewall 'holes' in the sonic image are filled in. You are then hearing those two speakers much more than the sounds bouncing off of the side walls.
When the two surround speakers are placed below ear level and tilted up at you, their sounds arrive much sooner than their own side wall reflections, which separates their sound even more from your room's sound.
You would think that by placing the surround speakers in front of you that you would miss the sound effects that are supposed to go through you and behind you. We wager that you will no longer care because your mind will then be acoustically busy with everything around you.
In real life, you mostly care about what is happening in your front visual field, including out to the limits of your peripheral vision. With the adjustments we recommend, the size of the acoustic field we have just supplied now matches your expectations of your visual world. Pretty neat, eh?
The 'Equal-Legged T' layout for the two main speakers allows them to blend just right for your two ears. On two channel music and soundtracks, you will not hear two speakers, but a uniform sound stage instead. If these speakers are any further apart, you will hear a hole in the middle -- one which the center channel speaker cannot fill in because it was never given the information.
In particular, you hear a hole in the middle because your right ear is not hearing enough of the left speaker, and vice versa.
When the two front speakers are closer together, the sound stage is miniaturized. It becomes much less real and engaging. The diagram here shows the 'Equal-Legged T' layout for the two speakers, and you can pace it off before you get out the tape measure.
Fine-tuning the setup
We recommend that you fine-tune the location of those two surround speakers with a well-produced concert DVD such as the Eagles' Hell Freezes Over (in DTS).
Ask two people to hold the two surround speakers high and low, tilted back and forth, moving from beside you to somewhat in front of you along the side walls. When the surround speakers are in their final positions, set their loudness by ear using that same DVD or another music DVD from a major artist.
Extra surround channels
If you have a third surround sound channel because you have a 6.1-channel control center, then place it at the center-rear of your room, probably above ear level, tilted down at you. Its exact height and tilt depend on how far away you are located. Adjust the control center's time delay so it is the same acoustic distance away from you as the two main front speakers.
When you have third and fourth surround channels as components of a 7.1-channel control center, place those two surround speakers on the side walls behind you about 15 degrees, about 1' (30cm) above ear level.
If these are direct-radiating speakers, toe them in so they cross right behind your head. Set their time delay again to match their acoustic distance to the real distance to the front main speakers.
Diffuse-field surround speakers
If your first two surround speakers are designed to bounce their sounds off the side walls (diffuse-field speakers, or 'di-pole,' or 'bi-pole') then try them with their tweeters either at or a little above ear level.
Again, ask two people to hold them up and move them along the sidewall. You may still prefer those two speakers in front of you by at least 5 degrees.
If the rear speakers of your 6.1 or 7.1 system are diffuse-field speakers, then follow the placement advice for them given above. Remember that it is always best to experiment with their placements.