[SoundStage!]Surrounded!
Back Issue Article

July 2003

Surround-Sound Speaker Placement: Problems and Solutions

Are you someone who's ready to experience multichannel music in all its glory but don’t know where to start? Don’t worry -- you’re not alone. There are lots of considerations, not the least of which is the additional living-room real estate a multichannel system will require. If you’re coming from a two-channel world, there’s just no getting around the fact that you’ll need space for the additional speakers.

There’s more to good surround-music reproduction than just plopping more speakers in a room, though. How can you guarantee that you hear what the recording was designed to have you hear? Are you coming from the home-theater side of things? There are issues there, too. Just having the right number of speakers doesn’t mean they’re in the right place or even designed for the correct purpose. Why can’t anything be simple?

Music in the theater

A typical home-theater system is not optimized for the playback of multichannel music. That’s not to say that many home theaters can’t convincingly reproduce a multichannel SACD or DVD-Audio disc; many can, but most aren’t explicitly set up for it, and for good reason. Home theaters -- discounting for a moment those that include projection systems, which are the vast minority -- all have in some form a monitor placed in a central position in front of the viewer. The speaker system’s placement, therefore, by necessity, is a secondary consideration next to the placement of the monitor. Because of this, compromises in system setup and configuration are introduced that negatively affect the reproduction of surround music. The biggest culprit is the center-channel speaker.

Let’s start in the center

The vast majority of center-channel speakers are designed to be placed above or below that direct-view monitor that most of us have. Their primary purpose is to anchor dialogue to the onscreen action for those viewers/listeners seated to the left and right of the monitor. This works pretty well because it prevents that off-axis listener from hearing a single stereo loudspeaker. For example, if the viewer were seated to the left of the screen, he would hear primarily the left speaker. The result would be dialogue diluted by the left channel’s sound.

So although suited for home theater, the monitor-sensitive center-channel speaker we’re all used to is a problem for multichannel music. Drat!

Most home theaters use a pair of stereo loudspeakers in the front left and right positions and a horizontally placed center-channel speaker above or below the monitor. This introduces several problems when multichannel music is played back. First and foremost, most multichannel recordings were not designed to be played back over a system configured around a monitor. Second, the horizontal center-channel speaker itself is not the best solution for the reproduction of the center-channel information present on multichannel-music recordings.

The International Telecommunication Union standard for multichannel recording and playback is very specific when it comes to speaker configuration and placement for playback of multichannel recordings (shown right). Many, if not most, recording engineers use this model when configuring their microphones and studio consoles. The ITU’s system setup calls for five identical speakers placed in an arc around the centrally located listener. The center-channel is therefore a duplicate of the front left and right speakers (so are the surrounds) in this model.

The problem with this setup as it applies to home-theater users with direct-view monitors is that a floorstanding or stand-mounted speaker, such as the vast number of stereo loudspeakers, can’t very well be placed in front of the screen. For most consumers this means that compromises have to be made if a system is to be used for home theater and multichannel music.

What’s wrong with typical center-channels? To oversimplify a bit, a horizontal center-channel speaker by design can’t exactly duplicate the response of the left and right main loudspeakers. This has to do with technical issues such as dispersion patterns (the way sound radiates from the loudspeaker in every direction), diffraction in conjunction with the monitor’s chassis (the way sound is changed when it encounters a new surface, in this case the TV), frequency response due to cabinet-size constraints (you can’t have a huge speaker on a small TV), and a whole slew other criteria. The bottom line is that a center-channel configured for a home theater won’t reproduce sound the way the multichannel-music recording engineer planned for. We’re, therefore, in need of a center-channel solution, but that’s not all.

Let’s move to the back

A similar compromise is made in the rear of the room. Instead of surround speakers identical to the mains, as dictated by the ITU, most home theaters use either bookshelf-type direct-radiators or dipole/bipole wall-mounted speakers designed to diffuse sound throughout the back half of the room. There isn’t typically as much musically significant information mixed into the surround channels, and it certainly isn’t as critical as a centrally placed vocalist as reproduced by the center-channel speaker, but nonetheless sonic problems arise.

The wildly different dispersion patterns created by dipole/bipole speakers, the interaction of wall-mounted surround speakers to their environment, and the frequency-response inconsistencies of the typically smaller cabinet sizes, create a set of unknowns just not fully accounted for in multichannel-music delivery systems. Good bass-management and time-delay adjustments can help with deficiencies in surround placement and design, but only so much. For example, although you can add time delay into surround speakers to compensate for distance anomalies in speaker placement, this function cannot correct for improper driver blending caused by too-close placement of the speaker to the listener’s head.

The diffuse sound of dipole/bipole speakers can alleviate to an extent the need for exact placement of surrounds in the home theater. Film soundtracks are designed for this type of playback system to begin with. Multichannel music recordings are not designed for speakers that deviate from the configuration of the main loudspeakers, nor placement inconsistencies as extreme as those found in many home theaters. So now we have problems with typical center-channels and surrounds when used for music. But what if you don’t have any of those speakers yet?

Starting from two

If you are coming from two channels into the world of multichannel music, the most obvious thing to do is set up a system compatible with the ITU diagram. For most people, this is not a no-brainer solution, however. Not many people reading this article are itching to go out and buy three more speakers identical to their mains. And that would only work if the space requirements were accommodated by the room layout. And what if (horrors!) you occasionally wanted to watch a concert DVD? You’d have no place for your television. Bummer.

Common-sense solutions?

The problems highlighted above raise more questions than they answer. With the seeming incompatibility of the generally accepted ITU standard for surround-music recording and playback versus the typical home-theater system, setting up a modern-day A/V system is almost overwhelming to the average consumer. There are some easy solutions, however, that although aren’t perfect, can make a lot of difference in the performance of your multichannel music/home-theater/stereo system.

The first suggestion is to forget reproducing super-low bass from your five primary channels. A subwoofer and good bass management can overcome a lot, especially if the 5.1 speaker array is designed as a system. This solution involves placing a small bookshelf-sized speaker in its correct vertical alignment atop your monitor (which would be the same as the speakers placed in the front left and right positions on stands). Two more of these speakers placed in the rear as surrounds and you’d have a perfectly matched array. The only thing you’re really giving up is low bass, due to the size restriction you’d have to place on the individual speakers.

Here's a tip: I’d suggest aligning your monitor (and perhaps find some good adjustable speaker stands) so that the front three loudspeakers can align properly. You don’t want the center-channel speaker placed above your head while the front left and right speakers are several inches lower, for example. Make sure the tweeters line up from right to left.

Another tip: If you have floorstanding stereo loudspeakers you just can’t give up, I’d suggest looking at the manufacturer’s other models to see what’s similar. You may find another direct-radiating loudspeaker that primarily deviates from your mains in the lowest of bass. This would make a close-to-ideal surround speaker for most recordings. It wouldn’t be perfect, but if it could be placed properly, it may be so close as to not cause an issue. This solution would also be compatible with home theater.

Lastly, instead of a severely compromised center-channel speaker, you can just forgo one altogether. With many recordings this works just fine depending on the recording-engineer’s mix. With good processing and the ability to route center-channel information into your front stereo pair, a centrally seated listener can enjoy the surround experience with only four speakers. This is my preferred speaker configuration, and I can tell you that using a "phantom" center channel can be a fantastic solution.

Don’t despair, just be creative

Barring a projection system with an acoustically transparent screen and five identical full-range speakers placed just so around the listener, there just aren’t many perfectly configured systems for all-‘round use. And how many of us have the ability to setup a system like that? You may not be able to playback everything out there as it was designed to be played, but you can get close by following these suggestions. And better yet, you’ll open up new possibilities to enjoy media you can’t enjoy with typical home theaters and stereo systems. Now doesn’t that sound like fun?

...Jeff Fritz
jeff@soundstage.com

 

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