Last time, we discussed how to optimize your room for the video features of your home theater. Now we come to the room configurations that will affect the audio performance of your home theater system. As with the video, the shape, furnishings and placement of windows and doors will affect the quality of the sound you get out of your system. We also have to revisit the placement of the many wires required to serve the speakers now placed all over your room. Just like everything else, relax and take it slowly. A little planning now will greatly enhance your enjoyment for a long time to come.
First, let’s look at some of the aspects of the room that are not so easy to change. For most of us we do not live in a mansion like Aaron Spelling with hundreds of rooms. This means the decision as to what room to use for our home theater will be very limited. We pretty much have to deal with the room we have. If at all possible, avoid a room that is basically square or where one dimension is close to twice the other. These configurations will create a pattern where the sound waves bounce back on themselves and either cancelled each other or overly reinforce themselves. In either case it distorts the sound creating overly bright or muddy sound. A little later on in this article we will go over some tricks of the trade to help compensate for factors like this that we can’t control.
Among the many aspects of the room that affect audio response is how close to the corner the speaker is placed. Sound waves bounce off of the corners increasing the sound, specifically the lower frequencies. This becomes particularly important if you are using the little satellite speakers. These speakers typically do not have much in the way of low-end performance. By placing them across a corner you will increase the perceived bass making the sound boom a little more. Now the reverse is also true. If you have a full response speaker, one with a tweeter, mid-range and woofer, placing it across a corner will increase the bass where you don’t need it making the sound come across as too dark and overpowering. By just moving the speakers a little out of the corner will help remedy this problem. In many systems there are larger speakers in the front with little ones used for the rear. Using the corner trick will help the bass for the rear it is better to have matched speakers all around. When I was able to move up to new speakers I got four full response speakers. The difference was move that I could have imagined. The sound they produced was much fuller, I really felt as if I was in the film.
We now come to the math portion of the curriculum. Don’t worry; this will not be on the test. With many systems it is possible to set the delay for the rear speakers. This is not required for discreet six or seven channel sound but it is important for ProLogic and other matrixed or emulation modes. With these modes the signal to the rear speakers is delayed slightly to emulate the natural reverberation of a room. The formula for setting this delay is as follows:
d1: distance from listening position to front speakers.
d2: distance from listening position to rear speakers.
If d1 is equal to or less than d2 set to 15ms.
If d2 is less than d1 start at 15ms and increase by 5ms for every 1.5 meters of difference between d1 and d2
As with everything else this is subject to what you, the person paying for all of this, finds acceptable. If a so-called expert what to determine these settings let them come across with some cash to help pay for it. Things like furniture, windows and doors will affect this so use this formula as a starting point. In a later article we will take a look at calibration discs that will help personalize and customize your system to your liking.
Now for a couple of simple audio terms to help us out with the rest of our set up. A room can be divided up into live and dead regions. They are also called bright and dark but personally I find that too ‘video’ for application here. A live area is one where there are a lot of hard, bare surfaces that can reflect sound. Naturally, this makes a dead area one with a lot of sound absorbing surfaces like drapes, carpet and upholstered furniture. With home theater’s surround sound you want to place the dead space in the front of the room to help the front and center speaker do a better job of localizing their sounds. Keeping the back of the room live diffuses the sound and helps with the surround speakers job of creating ambient sounds. There are trade offs required here. A live space in the rear will diminish the localization of discreet rear speakers. We also have to balance the concerns of optimizing the room for the video with those of the audio. If you need curtains to keep out the light for your TV you are creating a dead spot for the audio on that side of the room. No one said this was a perfect world, compromise is not an option here it is a way of life. Windows and plain walls are live. Drapes and doorways are dead. While doorways are rarely upholstered they have nothing to reflect sound so they act as the ultimate dead space. Your equipment was most likely designed and in perfect laboratory settings. Most of us do not have an acoustic lab in our homes so we have to rearrange some furniture and set up the speakers to compensate.
Here are some simple rules to help with your setup. Too many live areas will result in the sound reflecting creating a muddy sound especially with the dialogue. You should try to place the primary viewing position in the middle of the speaker. In my home this is where I sit. Remember Star Trek? Captain Kirk had the perfect setup, a comfortable seat in the middle of the room facing a large screen with a yeoman bringing him a drink. The speakers should be about one meter (three feet for the metrically challenged) from the floor. If you have really small speakers you can enhance the corner affect by placing them near the ceiling where there is an additional corner where the wall meets the ceiling. Place the sub woofer away from the main speakers. If they are set too close it can overwhelm the front speakers. Since most low frequency sound is difficult to locate the placement of the subwoofer is open to more variation. Move it around and listen to what seems best to you. The front center speaker is typically placed on top of the TV or directly in front of it. Aim it at your primary position. This means pointed up if it’s on the floor and slight down if on the TV. I have mine on top of the TV and use an old loose-leaf binder about one and a half inches think to point it slightly down.
The last thing to consider is for those of use that have made the move to seven-channel sound. You have a rear center speaker to consider. This means that your couch or chair cannot be up against a wall. You have to place the rear center speaker opposite the front center in line with the two rear speakers. This is also going to be a bit of a problem with running wires so its best to have a wall that runs between the rear speakers to avoid a wire in the middle of the room.
You can avoid all these problems with a merge $10,000 or so by having a contractor build the perfect room for you. For the rest of us a bit or re-arranging things will help you get the most out of your system.