Rules of Loudspeaker Placement

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Rules of Loudspeaker Placement

By Robert Harley

Correctly positioning your loudspeakers is the single most important thing you can do to improve your system?s sound. It?s free, and can make the difference between mediocre and spectacular sound with the same electronics and loudspeakers. Before spending money on upgrading components or acoustic treatments, be sure you?ve realized your system?s potential with correct loudspeaker placement.

To hear the full magic of a high-quality audio system, you?ll need to arrange your listening room in a way that allows the system to perform at its best. All the effort you?ve put into choosing a system (along with the money you spent on it) can be wasted without a correct fundamental setup. Positioning the speakers in roughly a triangle with the listener (more on this later) will get you in the ballpark and give your system a chance of being fine-tuned for optimum performance. At the next level, small loudspeaker movements within this fundamentally correct placement zone allow you to precisely dial-in the system.

Loudspeaker placement affects tonal balance, the quantity and quality of bass, soundstage width and depth, midrange clarity, articulation, and imaging. As you make large changes in loudspeaker placement, then fine-tune placement with smaller and smaller adjustments, you?ll hear a newfound musical rightness and seamless harmonic integration to the sound. When you get it right, your system will come alive. Best of all, it costs no more than your time.

Let?s look at the six fundamental factors that affect how a loudspeaker?s sound will change with placement. (Note that you should wait until after you?ve completed the entire loudspeaker placement procedure to install the loudspeaker?s floor-coupling spikes.)

Rule #1: The listener and loudspeakers should form a triangle; without this basic setup, you?ll never hear good soundstaging and imaging.

The listener should sit exactly between the two loudspeakers, at a distance away from each loudspeaker slightly greater than the distance between the loudspeakers themselves. Though this last point is not a hard-and-fast rule, you should certainly sit exactly between the loudspeakers; that is, the same distance from each one. If you don?t have this fundamental relationship, you?ll never hear good soundstaging from your system.

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Fig. 1 shows how your loudspeaker and listening positions should be arranged. The listening position?equidistant from the speakers, and slightly farther from each speaker than the speakers are from each other?is called the ?sweet spot.? This is roughly the listening position where the music will snap into focus and sound the best. If you sit to the side of the sweet spot, the soundstage will tend to bunch up around one speaker. This bunching-up effect will vary with the loudspeaker; some loudspeakers produce a wider sweet spot than others. When you sit exactly between the speakers, a ?phantom? center image is created; you hear a vocalist, for example, as coming from a position between the speakers. When you move off to the side, the vocalist?s image moves toward the speaker you are closer to.

Setting the distance between the loudspeakers is a trade-off between a wide soundstage and a strong center image. The farther apart the loudspeakers are (assuming the same listening position), the wider the soundstage will be. As the loudspeakers are moved farther apart, however, the center image weakens, and can even disappear. If the loudspeakers are too close together, soundstage width is constricted.

The ideal speaker separation will produce a strong center image and a wide soundstage. There will likely be a position where the center image snaps into focus, appearing as a stable, pinpoint spot exactly between the loudspeakers. A musical selection with a singer and sparse accompaniment is ideal for setting loudspeaker spacing and ensuring a strong center image. With the loudspeakers fairly close together, listen for a tightly focused image exactly between the two loudspeakers. Move the loudspeakers a little farther apart and listen again. Repeat this move/listen procedure until you start to hear the central image become larger, more diffuse, and less focused, indicating that you?ve gone slightly beyond the maximum distance your loudspeakers should be from each other for a given listening position.

Rule #2: The nearer the loudspeakers are to walls and corners, the louder the bass.

Loudspeakers placed close to walls will exhibit a reinforcement in the bass (called ?room gain?), making the musical presentation sound weightier. When a loudspeaker is placed near a wall, its bass energy is reflected from those walls back into the room essentially in phase with the loudspeaker?s output. This means the direct and reflected waves reinforce each other at low frequencies, producing louder bass. The closer to the corners the loudspeakers are placed, the more bass you?ll hear. A simple fix for boomy bass is to move the speakers out into the room farther from the rear and side walls.

The loudspeaker?s position in relation to the rear and side walls will also affect which frequencies are boosted. Correct placement can not only extend a loudspeaker?s bass response by complementing its natural rolloff, but also avoid peaks and dips in the response. Improper placement can cause frequency-response irregularities that color the bass. That is, some frequencies are boosted relative to others, making the bass reproduction less accurate. For this reason, the loudspeakers should be positioned at different distances from the rear and side walls. A rule of thumb: the two distances should not be within 33% of each other. For example, if the loudspeaker is 3? from the side wall, it should also be at least 4? from the rear wall.

Rule #3: The loudspeaker and listener positions in the room affect the audibility of room resonant modes.

Room resonant modes are reinforcements and cancellations at certain frequencies that create peaks and dips in the frequency response, which can add an unnatural boominess to the sound. When room resonant modes are less audible, the bass is better defined, and midrange clarity increases.

Speaker and listener position also affects the amount of bass the listener hears because of standing waves. These are stationary areas of high and low pressure in a room. If the listener is sitting in a standing-wave peak, the bass will be boomy. If sitting in a standing-wave null, the sound will be thin and lacking weight. The solution to either problem is to move the listening seat forward or backward until you hear just the right bass balance.

A well-known rule of thumb states that, for the best bass response, the distance between the loudspeakers and the rear wall should be one-third of the length of the room. If this is impractical, try one-fifth of the room length. Both of these positions reduce the excitation of standing waves and help the loudspeaker integrate with the room. Starting with these basic configurations, move the loudspeakers and the listening chair in small increments while playing music rich in low frequencies. Listen for smoothness, extension, and how well the bass integrates with the rest of the spectrum. When you find the loudspeaker placement where the bass is the smoothest, you should also hear an increase in midrange clarity and definition.

Rule #4: The farther out into the room the loudspeakers are, the better the soundstaging?particularly depth.

Generally, the farther away from the rear wall the loudspeakers are, the deeper the soundstage. A deep, expansive soundstage is rarely developed with the loudspeakers near the rear wall. Pulling the loudspeakers out a few feet can make the difference between poor and spectacular soundstaging.

Rule #5: Listening height affects tonal balance.

Most loudspeakers exhibit changes in frequency response with changes in listening height. These changes affect the midrange and treble, not the bass balance. Typically, the loudspeaker will be brightest (i.e., have the most treble) when your ears are at the same height as the tweeters, or on the tweeter axis. Most tweeters are positioned between 32? and 40? from the floor to coincide with typical listening heights.

The degree to which the sound changes with height varies greatly with the loudspeaker. Some models have a broad range over which little change is audible; others can exhibit large tonal changes when you merely straighten your back while listening. Choosing a listening chair that sets your ears at the optimum axis will help achieve a good treble balance. For stand-mounted speakers, selecting the right height for your speakers and listening position is vital.

Rule #6: Toe-in (angling the loudspeakers toward the listener) affects tonal balance, soundstage width, and image focus.

Toe-in is pointing the loudspeakers inward toward the listener rather than facing them straight ahead (see Fig. 3). There are no rules for toe-in; the optimum amount varies greatly with the loudspeaker and the listening room. Some loudspeakers need toe-in; others work best firing straight ahead. Toe-in affects many aspects of the musical presentation, including mid- and high-frequency balance, soundstage focus, sense of spaciousness, and immediacy.

12-3-toe-in.jpg

Most loudspeakers sound the brightest directly on-axis (directly in front of the loudspeaker). Toe-in therefore increases the amount of treble heard at the listening seat. An overly bright loudspeaker can often be tamed by pointing the loudspeaker straight ahead. Some models, designed for listening without toe-in, are far too bright on-axis.

A toed-in loudspeaker will present more direct energy to the listener and project less energy into the room, where it might reach the listener only after reflecting from room surfaces. As we?ll see later in this chapter, sound reflected from the sidewalls to the listening positions can degrade sound quality. Toe-in often increases soundstage focus and image specificity. When toed-in, many loudspeakers provide a more focused and sharply delineated soundstage. Images are more clearly defined, compact, and tight, rather than diffuse and lacking a specific spatial position. The optimum toe-in is often a trade-off between too much treble and a strong central image. With lots of toe-in, the soundstage snaps into focus, but the presentation is often too bright. With no toe-in, the treble balance is smoother, but the imaging is more vague.

Toe-in also affects the presentation?s overall spaciousness. No toe-in produces a larger, more billowy, less precise soundstage. Instruments are less clearly delineated, but the presentation is bigger and more expansive. Toeing-in the loudspeakers shrinks the apparent size of the soundstage, but allows more precise image localization. Again, the proper amount of toe-in depends on the loudspeaker, room, and personal preference. There?s no substitute for listening, adjusting toe-in, and listening again.
Identical toe-in for each loudspeaker is vital. This is most easily accomplished by measuring the distances from the rear wall to each of the loudspeaker?s rear edges; these distances will differ according to the degree of toe-in. Repeat this procedure on the other loudspeaker, adjusting its toe-in so that the distances match those of the first loudspeaker. Another way to ensure identical toe-in is to sit in the listening seat and look at the loudspeakers? inside edges. You should see the same amount of each loudspeaker cabinet?s inner side panel. Identical toe-in is essential to soundstaging because the speaker?s frequency response at the listening position changes with toe-in, and hearing the identical frequency response from each speaker is an important contributor to precise image placement within the soundstage.

Keep in mind that all loudspeaker placement variations are interactive with one another, particularly toe-in and the distance between loudspeakers. For example, a wide soundstage can be achieved with narrow placement but no toe-in, or wide placement with extreme toe-in.

The Final Touch

After you?ve found the best loudspeaker placement, install the carpet-piercing spikes (if any) supplied by the manufacturer. Level the spikes so that the loudspeaker (or the stands on which the speaker is mounted) doesn?t rock: the loudspeaker?s weight should be carried by all four (or three) spikes. If you have wood floors that you don?t want to mar with spikes, place the round metal discs that are often supplied with the loudspeakers beneath the spikes.

Loudspeaker positioning is a powerful tool for achieving the best sound in your listening room, and it doesn?t cost a cent. Take advantage of it.

Source: http://www.avguide.com/news/2007/03...the-six-rules-of-loudspeaker-placement-intro/
 
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