Deciding where to place your home theater speakers is probably something you have been wondering about. What placement will give me the optimal sound experience?

There are a few things to consider:

• Knowing about the acoustic behavior of waves
• Your room geometry configuration
• The type of speaker you have

Knowing about the acoustic behavior of waves

Waves propagate in air differently depending on their wavelength. Low frequency sounds tend to travel in all directions, propagating in the manner of a water drop. On the other end, high frequencies such as a police car siren or people voices will propagate in a straight line in front of the speaker it is emitted from.

Directionality of sound waves

This is important to understand as it will directly affect where we place each speaker based on the role of the given speaker. For instance, a sub-woofer speaker can be placed pretty much any where in your home theater room as it only emits low frequencies (in the range of 20 to 400 Hz typically). On the other end, speakers meant to reproduce the directional sounds in the scene should be placed so that they point toward the listeners as much as possible. This will be valid as much in term of their height placement as their position on the room floor. We will thus have to consider things in a 3D space.

Sound reflections

The other thing we will have to consider regarding sound wave propagation is... reflections. This is actually our enemy as we want to get rid of most of these sound reflections. Unfortunately, most home theater environments are constituted of painted gyps walls which are notoriously good at creating sound reflections. Even if you paid thousands to build sound insulated walls, they will still reflect sounds from inside your home theater room. We will see later on what we can do to limit these reflections.

Standing waves

Standing waves are waves that adopt a behavior where they seem to be static in space. A wave has various amplitudes depending on where you look at it in space and time. With a standing wave, the maximal amplitude "hills" of the wave are always standing at the same place in your room. Worse, as the wave travel back and forth from a side of your home theater room to the opposite, it sill create a build-up situation where the initial wave is superimposed to the one coming back and in effect, this will augment the amplitude of the initial wave. What will this cause? It will turn your room into a big resonance box for some specific frequencies which can be quite damageable to your home theater experience. We will see later-on how we can prevent this.

Now that we understand the basic behavior of our sounds, let's see how we can get more practical with regard to our home theater environment.

Your room geometry configuration

The ideal home theater room is rectangular as much as possible. There a few reasons for this. First, it allows us to more easily place our speakers as it is easier to understand the sound propagation behavior of our room. Secondly, the sound reflections are more symmetrical and predictable. This will be a plus in trying to reduce them. On the other hand, it will cause us a potential problem as a square or rectangular shaped room will tend to favor standing waves.

Usually, you want to position the main left and right speakers on each sides of your rear projection TV or front projection screen. The separation distance can be from 6 to 12 feet apart. The wider the placement of your speakers, the better it will be for the stereo separation. You can then either orient the speakers to face the listeners or to be parallel to the wall and send waves in a parallel fashion on each sides of the listener area. Try experimenting both scenarios and see which one sounds better to you.

As we said earlier, you want to place the speakers so that the tweeter (i.e., the small high-frequency speaker element) is located at hears height when your listeners are seated. This probably means about 3 feet above the floor in most situations. For the center speaker, we have to make compromises as it usually have to be placed on top of a tall rear projection TV set. That is okay, we will compensate later-on with the adjustments we make in the home theater amplifier unit. Make sure you buy a quality center speaker that is magnetically shielded. This will avoid encountering interferences as you place it near-by a TV set.

The last speakers to place are the rear ones. These are probably the trickiest ones to place. Dolby Laboratories recommend a few feet over the hearing position of the listeners. This is probably a good choice as background sounds are generally less precise in their 3D location and act more to add a general background mood. Nevertheless, you can try to put them closer to the hearing level and see what you prefer. Should you aim the speakers directly at the listener position or toward walls, etc? I tend to prefer to aim them to the listener, as long as you have at least 4 feet of distance from the speaker to the listener.

There is no unique solution to speaker placement in a given room, and experimentation is always a good idea. The general rule of thumb to do an audio test is to use a movie sequence where there are lots of high frequencies sounds such as voices. This will allow you to better feel the 3D nature of the sounds which is the important aspect to fine tune. In short, you mainly want to concentrate on tuning based on high frequencies rather than low frequency special effects booms and the likes.

The type of speaker you have

Ideally, you want to have a paired set of speakers as much as possible. Mixing different types or brands of speakers will lead to having different speaker specifications and behaviors when feed with an identical audio signal.  This is of course not desired as it will make it harder or impossible to tune your home theater sound field completely.

There are two types of speakers that can be used for a home theater:

• Satellite speakers

Satellite speakers are generally smaller and pretty much only capable to render high frequency sounds. Their job is to fill in the room of 3D spatial sounds as we say earlier. They are not there to render the large booms and other low frequency loud special effects. When using this type of speakers, you absolutely need a powerful sub-woofer to complete the range of frequencies that are reproducible. This type of speakers offers a good compromise between saving space and giving a great 3D sound field in your room. This being said, it is not the best choice if you intend to listen to music and not only movies.

• Tower speakers

Tower speakers are generally equipped with one or two 6 inches mid-frequencies speaker elements and are thus capable to reproduce a larger range of frequencies. The other bonus is that the tweeter in these speakers is generally located at about 3 feet above ground such that they are already well placed for optimal listening position while seated.  If you intend to listen to music as much as movies, this is probably your best option. You will have a better and more uniform coverage of all frequencies with this type of speakers.

Optimizing further your room for best sound reproduction

We can still further optimize the sound quality of our room by using what we know about sound propagation. We said earlier that reflections were something we want to get rid of. How can we? The first step is to limit the amount of flat reflective surfaces. A surface will be more reflective to sound as it is more even and soft. A rough and porous surface will not reflect as well sounds. It is the same as with light reflection from a glossy vs porous painted wall.

We may not be able to put 2 inch eggs foam on all our home theater room, but we can do some of the same effect using some specifically porous fabric curtains that we can hang on some walls of our room. While you are at it, use a black or dark colored fabric so that you also optimize the lighting ambiance of your room at the same time... More on this on another section. Side walls are particularly important to take care of. Next, the front wall where your TV or screen is located is another place where you may want to place a curtain.

Also keep in mind that room furniture such as sofas and tables act either as sound absorbers or reflectors too. Over cluttering a room with furniture can greatly distort the sound field of your room. As a general rule of thumb, keep it lean and simple.