July 2002

Surround Speaker Confusion -- Part Two: Speaker Placement

Last month we discussed the different types of surround speakers. The two most commonly used designs are dipolar and direct-radiating loudspeakers. To recap, dipolar designs are not intended to radiate sound directly toward the listener. They rely on reflected sound, which gives a more diffuse and non-localizable surround presentation. Direct-radiating designs, as the name implies, are meant to radiate sound directly toward the listener and provide precise imaging.

Both types of speakers have advantages and disadvantages when used in a surround-speaker array where the goal is to obtain the proper balance between enveloping surround ambience and having enough localization for directional surround effects. How you go about achieving this acoustic balancing act depends on many factors. The type of speakers that you choose, the layout of your room including how it interacts with those speakers, and the inconvenience that you are willing to endure all influence their final placement.

What the experts say

Contrary to what you might think, the originators of the surround-sound audio formats such as Dolby Labs and DTS and most hardware manufacturers offer little in the way of advice when it comes to the placement of surround speakers. This is probably because there are such a wide variety of variables that can affect the setup and placement of surround speakers.

Dolby Labs has some general guidelines pertaining to Dolby Digital EX (6.1 and 7.1) systems. They do not recommend any one type of speaker design over another, but they suggest that all of the speakers in a surround array be of the same or similar design. They also recommend the use of two center (sometimes referred to as "back") surround speakers and that all of the surround speakers should be situated at the same height and preferably above ear level.

The folks at THX seem to have proprietary specifications for nearly every other aspect of home theater, but they are also surprisingly silent when it comes to the subject of surround placement. According to John Dahl, certification and operations manager of THX Engineering, there are so many variables that trying to provide exact specifications for surround-speaker placement "would all too often be a self-defeating task." However, they do have some recommendations for surround placement that they have developed over the years. He shared them with me.

THX still advocates that dipoles be used for the left and right surrounds and that they be placed to the sides of the listener with the null pointed at the listening position. Now there is also a specification for direct-radiating surround speakers, which they recommend be placed to the sides of the listening position and pointed directly at each other, but high above the listeners’ ears. For Surround EX and DTS-ES, they recommend dipoles on the back wall, but again, direct-radiating speakers can be substituted. The latter would be placed high above the listeners and pointed over their heads, straight into the room. They acknowledge that dipoles used as back surrounds can be problematic if a listener is forced to sit in the direct-radiating region of one of these speakers. Finally, THX Ultra2 has a specification called THX ASA, where two direct-radiating back surround speakers can be placed side by side against the back wall, pointed straight forward, and made to sound like a very wide and diffuse source.

What Roger says

Most good surround speakers, regardless of design, can be made to work well in most rooms. However, it may take some experimentation and effort to get the placement of the speakers just right. While there may not be any hard and fast rules, there are some general guidelines that can be followed, and understanding why they work will make deciding on the best placement of your surround speakers much easier.

How high up should I place surround speakers?

Surround speakers are typically placed one or two feet above ear level, which is a good rule of thumb. Most surround speakers are bookshelf-sized speakers, so placing them on stands or wall mounting them at this height is commonplace and relatively easy to do.

Placing surround speakers above ear level, especially if they are direct-radiating designs, will help to make them less localizable, and provide a more enveloping soundfield. What you are trying to avoid here is having the tweeters level with, and pointed directly into, your ears, which will make the speakers extremely localizable.

Beside or behind you?

Surround speakers can work well when placed to the sides or behind the seating position. Direct radiators can be positioned to the sides and above the listening position, pointed directly at each other so that they radiate sound over the listeners’ heads. If the back wall is directly behind the seating position, the speakers can be placed in a similar fashion, with the sound radiating over and slightly behind the listeners. If the back wall is farther away from the seating position, the speakers can be angled toward the listeners and moved closer together if desired.

Because most people sit against the back wall in their home theaters, placing the surround speakers to the sides of the room usually provides the best distance from the speakers to the listener. If the surround speakers were placed on the back wall in this instance, there would be very little distance between the speakers and listening position. Some of the listeners might even be seated directly underneath a speaker!

Dipolar surround speakers are designed to be placed to the sides of the listening position, but they can also be placed behind the listener. The only caveat with this configuration is that some of the listeners might be situated in the null of the speaker while others could be in the direct-radiating zone, which would result in an uneven surround soundfield.

If you have a Surround EX/DTS-ES surround-speaker array, then the left and right surrounds will typically be placed to the sides of the listeners and the center surround(s) will be placed behind them.

How far away should the speakers be?

Ideally, each of the surround speakers should be the same distance from the listening position as the left and right mains and the center-channel speaker, but this is rarely the case, as most rooms used for home theater do not have the requisite space. However, most rooms have a greater distance from the listening position to the side walls than they do to the back wall, which is why side placement is often the preferred location for surround speakers.

Because dipoles utilize reflected sound, they can be placed closer to the listener than direct-radiating designs, which generally require more distance for the drivers to integrate (and can be localized if placed close to the listening position). This may be a consideration if you have limited space and cannot place the surround speakers very far from the listening position, especially if you have three or four speakers in a Surround EX/DTS-ES array.

Placing surround speakers far away from the listener presents the opposite problem: the sound becomes overly diffuse. If you are placing surround speakers on a wall that is a considerable distance away from the listening position, direct radiators may be a better option, as dipoles may sound too vague and indistinct.

Which way should I point the speakers?

Surround speakers should generally be pointed at the listener, except for dipoles, which are designed to utilize reflected sound. Direct-radiating speakers can be made to sound less localizable by placing them above ear level as recommended, or by angling them away from the seating position, or even by reflecting the sound off of room boundaries to disperse the sound. Conversely, if the sound is too diffuse with dipoles, they can be made to sound more localizable by angling one of the sides toward the listener. Changing the angle (or height) of any surround speaker in relation to the listening position is a good way of regulating how it sounds.

Walls or no walls?

Most people like to mount surround speakers on a wall, but stand placement may be your only option if you are lacking a wall on one or more sides of the room, or if there is a window or some other obstruction in the way. There is no reason why one surround speaker cannot be mounted on a wall and others placed on stands. Room boundaries such as walls tend to reinforce sound, so speakers placed near them will sound louder. This can be compensated for by adjusting the output levels of each channel on your receiver or processor.

Non-symmetrical rooms may also force you to place your surround speakers slightly closer to or farther away from the listening position, or at different heights. Again, this can be compensated for by adjusting the delays for each channel on your receiver or processor, and by tilting the speakers up or down slightly. Try to ensure that the distances and heights of all the surround speakers remain as close to each other as possible, and that these are also as close to the distances from the left and right mains and center-channel to the seating position as possible.

Be your own expert

Whether you prefer a diffuse and enveloping surround presentation or a more directional and localizable one, you should be able to obtain good results with a wide variety of surround speakers by following these general guidelines. Perhaps you’ll make a few discoveries of your own through some experimentation. Just remember that these are only suggestions, and that it will take some effort on your part to find the placement for your surround speakers that best suits your requirements.

...Roger Kanno
roger@hometheatersound.com

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