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MATCHING SPEAKERS TO YOUR ROOM

By George McKechnie

Whether listening to your favorite music or a blockbuster movie, the way in which the speakers are matched to your room, positioned in it, and tuned to its acoustic properties are critical to achieving the immersive and emotionally satisfying home entertainment experience you want.  Equally important to high quality sound are the design and built quality of the loudspeakers themselves —factors that are explored in depth in the companion Insights report Understanding Loudspeaker Differences.  Here the focus is on room-related factors that help to optimize the final sound experience:

  • Listening position, relative to the speakers (and TV)
  • Speaker locations, relative to walls, corners, shelves & cabinets
  • Speaker tuning, relative to the room and subwoofer
  • Room acoustics (floor & window coverings, upholstered furniture)

Listening Position.   Whether the system will be used for home theater, music, or both, the position of the speakers relative to the listener and TV is critical.  For home theater applications, the designer’s goal is to create a wide sweet spot—the region in which listeners can enjoy clear dialog and an immersive surround sound experience.  For stereo sound, the sweet spot is often deliberately narrowed—perhaps to the width of a single seat!

In a surround sound system, the task of the center speaker is to reproduce the main voice dialog, as it is reflected visually by the TV image.  So it should be positioned within the left/right limits of the TV itself.  In the vertical plane, the center speaker can be located below or above the TV, or even in the ceiling—so long as it is within the horizontal limits of the TV image.  Otherwise the dialog will sound as if it is being spoken off-stage—like lines delivered from the wings of a theatrical stage.  If positioning a center speaker within the horizontal boundaries of the TV is not feasible for physical or aesthetic reasons, using twin center speakers placed symmetrically to the left and right of the TV is a good alternative, (provided the surround receiver is capable of driving a pair of center speakers).

For a surround sound system, positioning the left & right speakers is not as critical as it is for stereo speakers.  In the latter, careful positioning is needed to optimize stereo “imaging.”  This is the sonic illusion of being in a venue where the musicians are spread out, left to right and front to back, before the listeners—rather than sitting in a living room where two boxes are pounding out loud (but not spacious or integrated) blasts of sound.  In a well-executed installation, the job of the center and surround speakers is to create a convincing illusion of space.  This frees up the left and right speakers to be much more flexibly placed than with a stereo system.

An extreme example of left/right speaker placement is found in the sound bar.  This approach places the left and right channel speakers within the width of the TV itself.  But with sufficient support from well-positioned surround (and even rear) speakers plus subwoofer, sound bars can do a creditable job of helping to create a satisfying sonic illusion of space.

What about optimal placement for the surround speakers?  Depending on the physical parameters of the room, surround speakers (in a 5.1 system) can be placed on side walls if practical (using either in-wall or on-the-wall units), in the ceiling (using built-in speakers), or even sitting on furniture, shelves or wall brackets to the left and right of the listeners.  A 7.1 (or higher) system adds rear channel speakers.  They belong behind the listeners—typically on or in the wall of the room opposite the TV, or in the ceiling above.

Both the position of the speakers and their tuning are critical.  They should be located far enough back in the room (above the listener or to the left and right) so that their sound is not perceived as coming from the front of the room.  Equally important, the volume level for the surrounds (and rears) should be adjusted so that they are heard only when actual surround sound effects have been encoded into the soundtrack.

Except for big special effects like car crashes, explosions, and airplane takeoffs, the surround speakers are intended to provide subtle spatial cues to reflected sound from above and/or behind the listener.   Too often consumers expect that there will always be sound coming out of their surround (and rear) speakers—regardless of the content and the sound engineer’s intent for a given scene.  When this does not happen, they may feel cheated that they aren’t getting full value from their surround speakers, and turn the surround level up so they can always hear something coming out of them (even if it’s just sonic artifacts from the front channels).

Some consumers also expect surround effects when playing stereo sources—even though such effects were never encoded in two-channel material.  Incidentally, most older video content was released with a stereo sound track, and much of this has not yet been re-mixed into surround sound.   Some surround receivers do have the capability to synthesize surround effects from stereo sources, and if this is desired, the system can be configured to do so.  But don’t confuse this with true surround sound.

Speaker Location.   In the Listening Positions section (above), we focused on the correct placement of speakers relative to the listener (and TV), so that an auditory sense of spaciousness—the hallmark of surround sound—is naturally and convincingly presented to the listener.  The goal of this section is different but complimentary: to help consumers avoid speaker placements that will acoustically alter the frequency balance of the sound, making it seem unnatural.

Here are two simple exercises that illustrate how easy it is to make the human voice—as well as other instruments—sound unnatural:

  • Recruit a male associate with a deep voice. Have him face an inside corner of your room, then walk slowly into the corner— beginning about 4 feet away—while speaking in his normal voice.  Notice that the closer he gets, the deeper and richer his voice sounds.  [This is why people like to sing in the shower—all those close corners add impressive (but unnatural) richness to the voice.]
  • Create a megaphone with your hands surrounding your lips (as though you’re calling to a friend across a large room), and then speak in your normal voice to an associate. It will sound unnatural to them, and to you, too.

The usual suspects for compromised speaker placement are corners and cavities.  If you place a speaker in a room corner (or worse, on the floor in a corner), the junction of the large surfaces will emphasize the mid-bass frequencies—just like singing in the shower.  This is called a boundary effect, and occurs at low frequencies, regardless of the speaker type.

Some high-quality speaker brands design a special compensation circuit into the crossover network of their speakers to correct for boundary effects when the need arises.  If a bookshelf, in-wall or in-ceiling speaker must be placed closer than about 18-24 inches from a corner, the mid-bass frequencies will be exaggerated, and the speaker will sound unnatural.  Turning on the boundary switch (if available) will “lean” out the sound, and the sense of musical heaviness will go away.

If the boundary compensation switch is turned on for a speaker that is not placed too close to a corner, the low frequencies will sound anemic.  Boundary effects are important in subwoofer placement, too.  In fact, they can be critical in subwoofer tuning.  See Subwoofer Tuning and Room Acoustics

If a speaker is placed on (or in) a bookshelf, or into a cabinet compartment, the enclosed space around and behind the speaker will alter the sound of the speaker.  Here’s why.  Not all of the sound coming from a box speaker radiates directly into the room.  Some wraps around the speaker, hits the wall, and is reflected back into the room.  If the speaker is placed into a cavity, that space will emphasize (or resonate) the sound at frequencies determined by the dimensions of the space.  The altered sound is then reflected out into the room, coloring the timbre of the sound the listener hears—like the megaphone effect created when cupping hands around the mouth.

These cavity resonances detract from the neutral reproduction of the music.  Fortunately, they can easily be corrected.  If the speaker must be placed on (or in) a bookcase, surround it with books—to fill up the cavity.  If the speaker is placed in a cabinet, buy closed cell foam and cut it to form an inverted U-shaped “collar” that fits snugly around the speaker and blocks the sound from reaching the space behind.  This will prevent sounds from exciting the cavity and creating unnatural resonances.   Or block off the front of the cavity with plywood, and mount an in-wall type speaker in the plywood—in effect converting the cavity into an enclosure.

Speaker Tuning.   Although most speakers lack the built-in tuning controls (level, frequency, and phase) available on most subwoofers, they can nonetheless be tuned to the room and other components in the system by using control options built into the surround receiver.  Also, some speaker models include level controls to adjust the tweeter and, in some cases, midrange level to the room acoustics.

Tone controls in the surround receiver can help compensate for frequency balance deficiencies in the speaker itself and for resonant problems due to non-optimal room placement or extreme room acoustics.   Balance controls can compensate for rooms that are highly reflective on one side wall (due to undraped windows or artwork behind glass, for example) or highly damped on the other (due to tapestries or fabric wall coverings), or for rooms where one side opens to an adjacent room or alcove but the other side does not.  Configuration adjustments in the receiver can even compensate for lip-sync problems which occur when the center speaker must be placed in front of or behind the plane of the TV screen.  For more on this topic, see Friending your Surround Receiver  (coming soon)

The other important aspect of speaker tuning involves adjusting the subwoofer level and transient response to the main speakers.  This important topic is dealt with in detail in Subwoofer Tuning and Room Acoustics.  With regard to tuning the low end of the main speakers, two points are worth noting.

First, most surround receivers allow the user to configure the low frequency roll-off to the left and right front speakers in the set-up menu.  This control is typically pretty primitive, consisting of telling the receiver whether the speakers are large or small.  If “small” is selected, the digital decoding chip inside the surround receiver rolls off the signal to the left and right speakers at 80 Hz.  For the “large” setting, the receiver may not roll off the output at all, allowing the speakers to run full range.

Second, some subwoofers provide the option of running the receiver outputs for left and right channels into the subwoofer first, where the built-in crossover contour these signals to the same crossover frequency selected for the subwoofer itself, then feeds the signal to the speakers.  For some speaker installation set-ups, this flexibility can be valuable in optimizing the mid-bass sound.

Room Acoustics.   Depending on a number of factors—most involving architecture or interior design—the room itself can dramatically influence the quality of the sound.  These acoustical factors can make it more reverberant than a hall of mirrors, deader than a carpet showroom, or somewhere in between.  The goal for room acoustics is midway between these extremes.

For dedicated home theaters, careful attention to the acoustics of the room is an integral part of the total design process.  But most home theaters are installed in spaces that double as living or family rooms.  Creating an immersive sonic experience in these everyday (untreated)  acoustical environment requires careful attention to these elements:

  • Floor & window coverings
  • Window sizes and locations
  • Furniture placement, quantity and upholstery
  • Wall coverings
  • Absorptive or reflective objects (overstuffed bookcases vs glass-covered artwork)

A typical living/family room—furnished with wall-to-wall carpeting, lots of upholstered furniture, and a picture window—is too absorptive from the floor up to the top of the seat backs.  Above this height, it is generally too reflective.  When such a venue is to double as a home theater, the goal is to balance out the quantity and location of absorptive vs reflective elements, while retaining its character and practical everyday usefulness as a room.

Small changes can bring about big sonic improvements.  These might involve: adding window drapes to reduce the reflectivity of large glass surfaces, re-positioning a collection of large glass-mounted picture frames, moving an over-stuffed love seat or replacing it with a pair of wood chairs, or replacing old wall-to-wall carpeting with area rugs strategically placed to help tune the room for optimal sound.  Sometimes hanging a quilt or other fabric covering on the wall opposite the main speakers is useful to tone down an especially reverberant room.

Summary.   Matching speakers to your room can involve a lot of effort—in planning the work, selecting the right kind of equipment, then executing the plan and tuning the system.  But the sonic rewards can be very great—and they keep paying back year after year.  If all this seems too complex for you to handle on your own, consider hiring a local expert to advise you.  It can take a lot of uncertainty, effort, and anxiety out of the process.  See the Dealer Finder to locate an expert in your area.