|Home | Audio Magazine | Stereo Review magazine | Good Sound | Troubleshooting|
How an audio system is set up has an enormous effect on the system’s sound quality. In fact, system set-up is an art that can turn a mediocre-sounding system into one that sounds spectacular. A budget system that is expertly set-up will often outperform a more costly one that has not been assembled with such expertise.
I’m fortunate to have learned the art of system set-up from the world’s great experts—the designers of high-end audio products. In the course of my work as a an A/V equipment engineer and reviewer since 1984, I’ve had a succession of designers bring their products to my listening room for review. As you can imagine, the designer or company representative is highly motivated to make his product perform at its best for the review. From each of them I’ve learned different techniques for squeezing the most performance out of an audio system. I’ll share with you these “tricks of the trade.”
In this section, I’ll guide you through the steps in setting up a system and tuning it for the best possible sound. The techniques presented in this section should be used in conjunction with the critical listening criteria described here. You will often make a change to the system, listen to evaluate the results, and make another change in a repetitive process until the system has achieved its full potential.
We’ll also spend quite a bit of time in this section on room acoustics and how you can use common domestic materials such as rugs and bookcases to improve your room’s sound.
Although it’s enormously rewarding to turn a decent-sounding system into a great-sounding one using only your skill and knowledge, such tweaking isn’t for every one. Many music lovers would rather just enjoy the music and avoid the hands-on aspects of system set-up. For those readers, there’s no substitute for the help of a skilled and caring dealer. Most dealers will come to your home and install a system you’ve purchased from them, and the good ones will spend the time to coax the best performance from it.
Your first decision in system set-up is where to put the equipment, the loudspeakers, and the listening chair or couch. If your audio system is also used for home theater, many of these factors will have been decided by your television’s location. Although this section focuses on left- and right-channel speaker placement and room acoustics, that basic set-up should serve as a foundation for adding a center-channel speaker, a subwoofer, and surround speakers for film-soundtrack reproduction or multichannel music. More detail on surround-sound set-up.
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 with out 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.
Finding the right spot for your loudspeakers is the single most important factor in getting good sound. 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 a few hours of your time.
Before getting to specific recommendations, let’s cover the six fundamental factors that affect how a loudspeaker’s sound will change with placement. (Later we’ll look at each of these factors in detail.) Note that you should wait until after you’ve completed the entire loudspeaker placement procedure to install the loudspeaker’s floor-coupling spikes.
1) The relationship between the loudspeakers and the listener is of paramount importance. The listener and loudspeakers should form a triangle; without this basic setup, you’ll never hear good soundstaging and imaging.
2) Proximity of loudspeakers to walls affects the amount of bass. The nearer the loud speakers are to walls and corners, the louder the bass.
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.
4) The farther out into the room the loudspeakers are, the better the soundstaging— particularly depth.
5) Listening height affects tonal balance.
6) Toe-in (angling the loudspeakers toward the listener) affects tonal balance (particularly the amount of treble), soundstage width, and image focus.
Let’s look at each of these factors in detail.
1) Relationship between loudspeakers and listeners
The most important factor in getting good sound is the geometric relationship between the two loudspeakers and the listener (we aren’t concerned about the room yet). 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.
Fig below 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 he. As the loudspeakers are moved farther apart, however, the center image weakens, and can even disappear. It the loudspeakers are too close together, soundstage width is constricted.
The ideal speaker separation will produce a strong center image and a wide sound. 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.
Note that adding a center-channel speaker for multichannel music or home theater reproduction makes the left-right placement less critical. The center speaker “fills in” the soundstage center, as well as broadens the sweet spot. This so-called “hard” center channel is contrasted with the “phantom” center channel created by your brain. When sitting between two speakers, you hear images coming from between the speakers, just as though a speaker were there. The phantom center channel is more fragile (the speaker and listener locations must be just right), but just as convincing. In addition, the vast majority of music recordings are in two-channel stereo; creating a multichannel mix from a two-channel recording involves signal processing (Dolby Pro Logic IIx or DTS Neo:6 Music, for examples) that many audiophiles are unwilling to use. This signal processing is provided only in home-theater controllers and A/V receivers, not in two-channel preamplifiers. Also consider that those two-channel recordings were created over a two-channel system and were meant to be played back over two loudspeakers.
A factor to consider in setting this angle is the relationship to the room. You can have the same geometric relationship between loudspeakers and listener with the loudspeakers close together and a close listening position, or with the loudspeakers far apart and a distant listening position. At the distant listening position, the listening room’s acoustic character will affect the sound more than at the close listening position. That’s because you hear more direct sound from the loudspeaker and less reflected sound from the room’s walls. Consequently, the farther away you sit, the more spacious the sound. The closer you sit, the more direct and immediate the presentation. Some loudspeakers need a significant distance between the loudspeaker and the listener to allow the loudspeakers’ individual drive units to integrate. If you hear a large tonal difference just by sitting closer, you should listen from a point farther away from the speakers.
2) Proximity to walk affects the amount of bass
The room boundaries have a great effect on a loudspeaker’s overall tonal balance. Loudspeakers placed close to walls will exhibit a reinforcement in the bass (called “room gain”), making the musical presentation weightier. Some loudspeakers are designed to be near a rear wall (the wall behind the speakers); they need this reinforcement fur a natural tonal balance. These loudspeakers sound thin if placed out into the room, others sound thick and heavy if not at least 3’ from the rear and side walls. Be aware of which type you’re buying if your placement options are limited.
When a loudspeaker is placed near a wall, its bass energy is reflected 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.
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.
3) Loudspeaker and listener ,positions affect room-mode audibility
In addition to deepening bass extension and smoothing bass response, correct loud speaker placement in relation to the room’s walls can also reduce the audible effects of your room’s resonant modes. Room resonant modes are reinforcements and cancellations at certain frequencies that create peaks and dips in the frequency response. In addition, loudspeaker and listener placement affect standing waves, which are stationary patterns of high and low sound pressure in the room that color the sound. The standing-wave patterns in a room are determined both by the room’s dimensions and by the position of the sound source in the room. By putting the loudspeakers and listener in the best locations, we can achieve smoother bass response.
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.
You should also experiment with moving the listening seat forward and backward to adjust the amount of bass you hear. If the sound is boomy, you could be sitting in a standing wave peak; if the sound is thin, the listening seat could be in a standing wave null. The solution is to move the listening seat to achieve just the right bass balance.
4) Distance from rear wall affects sound-staging
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. Unfortunately, many living rooms don’t accommodate loudspeakers far out into the room.
5) Listening be and 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. If you’ve got an adjustable office chair, you can easily hear the effects of listening axis on tonal balance.
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. Changing a listening chair that sets your cars at the optimum axis will help achieve a good treble balance.
Toe-in is pointing the loudspeakers inward toward the listener rather than facing them straight ahead (see Fig. below). 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.
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 section, 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 p 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.
Dipolar and Bipolar Loudspeaker Placement
Dipolar loudspeakers produce sound to the rear as well as to the front. An electrostatic speaker is a dipole because the vibrating diaphragm sits in open space rather than in a cabinet, launching sound equally to the front and rear. This rear wave from dipolar speakers is out of phase with the front wave; that is, when the diaphragm moves for ward to create positive pressure in front of the diaphragm, it creates negative pressure behind the diaphragm.
A bipolar speaker typically uses arrays of conventional dynamic drivers on the front and rear of the loudspeaker enclosure. The front and rear waves from a bipolar speaker are in phase with each other. That’s the difference between dipolar and bipolar: a dipole’s rear wave is out of phase with the front wave, and a bipole’s rear wave is in phase with the front wave.
Both of these speaker types are covered in detail in Sections 9 and 10. What concerns us here, however, are the special placement requirements of bipolar and dipolar loudspeakers, along with the different ways in which they interact with the listening room.
The most important consideration when positioning dipoles is that the wall behind the speakers (the rear wall) has a much greater influence on the sound than it does with conventional point-source speakers (those that direct energy in only one direction). Conversely, how the sidewalls are treated is less important with dipoles because they radiate very little energy to the sides; (this image shows the dispersion patterns of point-source and dipolar speakers.)
Generally, dipoles like a reflective rear wall, but with some diffusing objects behind the speaker to break up the reflected energy. A highly absorbent rear wall defeats the purpose of a dipole; that reflected energy is beneficial, and you want to hear it. But if the wall is flat and lacks surfaces that scatter sound, the reflected energy combines with the direct sound in a way that reduces soundstage depth. Bookcases directly behind dipolar speakers help diffuse (scatter) the rear wave, as do rock fire places, furniture, and other objects of irregular shape.
Dipolar loudspeakers also need to be placed farther out into the room than conventional point-source speakers. You can’t put dipoles near the rear wall and expect a big, deep soundstage. Be prepared to give up a significant area of your listening room to dipolar speakers.
Subwoofer Placement and Setup
It’s relatively easy to put a subwoofer into your system and hear more bass. What’s difficult is making the subwoofer’s bass integrate with the sound of your main speakers. Low bass as reproduced by a subwoofer’s big cone can sound different from the bass reproduced by the smaller cones in the left and right speakers. A well-integrated sub- woofer produces a seamless sound, no boomy thump, and natural reproduction of music. A poorly integrated subwoofer will sound thick, heavy, boomy, and unnatural, calling attention to the fact that you have smaller speakers reproducing the frequency spectrum from the midrange up, and a big subwoofer putting out low bass.
Integrating a subwoofer into your system is challenging because the main speakers may have small cones, and the subwoofer has a large and heavy cone. Moreover, the subwoofer is optimized for putting out lots of low bass, not for reproducing detail. The main speakers’ upper bass is quick, clean, and articulate. The sub-woofer’s bass is often slow and heavy.
Achieving good integration between small speakers and a subwoofer is easier if you buy a complete system made by one manufacturer. Such systems are engineered to work together to provide a smooth transition between the subwoofer and the main speakers. Specifically, the crossover network removes bass from the left and right speakers, and removes midrange and treble frequencies from the signal driving the sub- woofer. If all these details are handled by the same designer, you’re much more likely to get a smooth transition than if the subwoofer is an add-on component from a different manufacturer.
If you do choose a subwoofer made by a different manufacturer, several controls found on most subwoofers help you integrate the sub into your system. One control lets you adjust the crossover frequency. This sets the frequency at which the transition between the subwoofer and the main speakers takes place. Frequencies below the crossover frequency are reproduced by the subwoofer; frequencies above the crossover frequency are reproduced by the main speakers. If you have small speakers that don’t go very low in the bass and you set the crossover frequency too low, you’ll get a “hole” in the frequency response. That is, there will be a narrow band of frequencies that aren’t reproduced by the woofer or the main speakers. In a two-channel music system, the crossover will likely be inside the woofer, in a system designed for home theater as well as music, the crossover will be inside the A/V controller or A/V receiver.
Setting the subwoofer’s crossover frequency too high also results in poor integration, but for a different reason. The big cone of a subwoofer is specially designed to reproduce low bass. When it is asked to also reproduce upper-bass frequencies, those upper-bass frequencies are less clear and distinct than if they were reproduced by the smaller main speakers. Finding just the right crossover frequency is the first step in achieving good integration. Most subwoofer owner’s manuals include instructions for setting the crossover frequency. As a rule of thumb, the lower the subwoofer’s crossover is set, the better.
Some subwoofers also provide a knob or switch marked Phase. To understand a subwoofer’s phase control, visualize a sound wave being launched from your sub- woofer and from your main speakers at the same time. Unless the main speakers and subwoofer are identical distances from your ears, those two sound waves will reach your ears at different times, or have a phase difference between them. In addition, the electronics inside a subwoofer can create a phase difference in the signal. The sub- woofer’s phase control lets you delay the wave generated by the subwoofer so that it lines up in time with the wave from the main speaker. When the sound waves are in- phase, you hear a more coherent and better-integrated sound.
One way of setting the phase control is to sit in the listening position with music playing through the system. Have a friend rotate the phase control (or flip the phase switch) until the bass sounds the smoothest.
But there’s a much more precise way of setting the phase control that guarantees perfect phase alignment between the subwoofer and main speakers. First, reverse the connections on your main loudspeakers so that the black speaker wire goes to the speaker’s red terminal, and the red speaker wire goes to the speaker’s black terminal. Do this with both speakers. No from a test CD that includes pure test tones, select the track whose frequency is the same as the subwoofer’s crossover frequency. Sit in the listening position and have a friend rotate the subwoofer’s phase control until you hear the least amount of bass. The subwoofer’s phase control is now set perfectly. Return your speaker connections to their previous (correct) positions: red to red, black to black.
Here’s what’s happening when you follow this procedure: By reversing the polarity of the main speakers, you’re putting them out of phase with the subwoofer. When you play a test signal whose frequency is the same as the subwoofer’s crossover point, both the sub and the main speakers will be reproducing that frequency. You’ll hear minimum bass when the waves from the main speakers and subwoofers are maximally out of phase. That is, when the main speaker’s cone is moving in, the subwoofer’s cone is moving out. The two out-of-phase waves cancel each other, producing very little bass. Now, when you return your loudspeakers to their proper connection (putting them back in-phase with the subwoofer), they will be maximally in- phase with the subwoofer. This is the most accurate method of setting a subwoofer’s phase control because it’s much easier to hear the null rather than the peak. Unless you move the subwoofer or main speakers, you need to perform this exercise only once.
You can also get more dynamic impact and clarity from your subwoofer by placing it close to the listening position. Sitting near the subwoofer causes you to hear more of the sub’s direct sound and less of the sound after it has been reflected around the room. You hear—and feel—more of the low-frequency wave launch, which adds to the visceral impact of owning a subwoofer. Bass impact is more startling, powerful, and dynamic when the subwoofer is placed near the listening position.
Subwoofer placement also has a large effect on how much bass you hear and how well the sub integrates with your main speakers. When a subwoofer is correctly positioned, the bass will be clean, tight, quick, and punchy. A well-located subwoofer will also produce a seamless sound between the sub and the front speakers; you won’t hear the subwoofer as a separate speaker. A poorly positioned subwoofer will sound boomy, excessively heavy, thick, lacking detail, slow, and have little dynamic impact. In addition, you’ll hear exactly where the front speakers leave off and the subwoofer takes over.
Some general guidelines for subwoofer placement: As with full-range speakers, avoid putting the subwoofer the same distance from two walls. For example, if you have a 20’-wide room, don’t put the subwoofer 10’ from each wall. Similarly, don’t put the subwoofer near a corner and equidistant from the side and rear walls. Instead, stagger the distances to each wall. Staggering the subwoofer’s distance from each wall smoothes the bass because the frequencies being reinforced by the wall are randomized rather than coincident.
Multichannel Loudspeaker Placement
So far, we’ve discussed the placement of two loudspeakers for stereo music reproduction. With multichannel music and home theater becoming increasingly common, let’s expand on these loudspeaker-placement principles to include positioning more than two loudspeakers.
The optimum loudspeaker radiation pattern (uni-polar, dipolar) and configuration differ for multichannel music reproduction and home theater. For multichannel music, the ideal loudspeaker array is five identical full-range loudspeakers placed equidistant from the listener. For film-soundtrack reproduction, the center loudspeaker is typically smaller and lacks bass extension, and the surround speakers are dipolar types mounted on the sidewalls. Loudspeaker arrays optimized for home theater also include a subwoofer.
Let’s first look at the ideal multichannel music loudspeaker array. The center loudspeaker should be positioned on the room’s center-line directly in front of the listening position, and slightly behind the plane of the left and right loudspeakers. This placement creates a gentle arc, and puts the center loudspeaker at the same distance from the listener as the left and right loudspeakers. If the three front loudspeakers were lined up, the sound from the center speaker would reach the listener before the sound from the left and right speakers.
The rear-channel speakers should be located at 135 - 150° is shown below and at the same distance from the listener as the front three loudspeakers. This placement isn’t always practical, however, so many multichannel products provide a rear-channel delay for those situations in which the listener must sit closer to the rear loud speakers. Delaying the signals to the rear channels causes the sound from the rear speakers to reach the listener at the same time as sound from the front speakers.
With this array, the front left and rear left loudspeakers can produce phantom images between them along the left sidewall, and the front right and rear right loud speakers create phantom images along the right sidewall. Correct loudspeaker placement helps to achieve a soundfield that appears to be continuous from front to back, rather than as two separate sound-fields at the front and rear of the room.
Loudspeaker arrays optimized for film-soundtrack reproduction usually employ dipolar surround loudspeakers rather than point-source loudspeakers. Dipolar speakers produce sound equally to the front and rear; when positioned on the side- walls, the listener hears sound from the surround speakers only after it has been reflected from the room’s boundaries. This simulates the array of multiple surround speakers in a movie theater from just two surround speakers, and creates a greater feeling of envelopment. (Section 10 includes more detailed info on multichannel speaker placement for home theater.)
Loudspeaker Placement Summary
Loudspeaker placement is the single most important thing you can do to improve your system’s sound. It’s free, helps develop listening skills, 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.
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 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.
You’ve seen how loudspeaker placement gives you precise and independent control over different aspects of the music presentation. You can control both the quantity and the quality of the bass by changing the loudspeakers’ distances from the rear and side walls. The audibility of room resonance modes can be reduced by finding the best spots for the loudspeakers and listening chair. Treble balance can be adjusted by listening height and toe-in. The balance between soundstage focus and spaciousness is easily changed just by toeing-in the speakers. Soundstage depth can be increased by moving the speakers farther out into the room.
We’ve had the privilege of watching some of the world’s greatest loudspeaker designers set up loudspeakers in our listening room for review. At the very highest levels of the art, tiny movements—half an inch, for example—can make the difference between very good and superlative sound. The process can take as little as two hours, or as long as three days. We’ve often had the experience of thinking the sound was excel lent after half a day of moving the loudspeakers, only to discover that the loudspeaker was capable of much greater performance when perfectly dialed-in.
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.
Optimizing Your Listening Room
The room in which music is reproduced has a profound effect on sound quality. In fact, the listening room’s acoustic character should be considered another component in the playback chain. Because every listening room imposes its own sonic signature on the reproduced sound, your system can sound its best only when given a good acoustical environment. An excellent room can help get the most out of a modest system, but a poor room can make even a great system sound mediocre.
Common Room Problems and How to Treat Them
Treating your listening room can range from simply hanging a rug on a wall to installing specially designed acoustic devices. Large gains in sound quality can be realized just by adding—or moving—common domestic materials such as carpets, area rugs, and drapes. This approach is inexpensive, simple, and often more aesthetically pleasing than installing less familiar acoustic products.
Here are some of the most common room problems, and how to correct them.
1) Untreated parallel surfaces
Perhaps the most common and detrimental room problems is that of untreated parallel surfaces. If two reflective surfaces face each other, flutter echo will occur. Flutter echo is a “pinging” sound that remains after the direct sound has stopped. If you’ve ever been in an empty, uncarpeted house and clapped your hands, you’ve heard flutter echo. It sounds like a ringing that hangs in the air long after the clap has decayed.
Flutter echo is easy to prevent. Simply identify the reflective parallel surfaces and put an absorbing or diffusing material on one of them. This will break up the repeated reflections between the surfaces. The material could be a rug hung on a wall, a carpet on the floor (if the flutter echo is between a hard floor and ceiling), drapes over a window, or an acoustically absorbent material applied to a wall.
2) Uncontrolled floor and side-wall reflections
It is inevitable that loudspeakers will be placed next to the room’s side walls and near the floor. Sound from the loudspeakers reaches the listener directly, in addition to being reflected from the side walls, floor, and ceiling. Side-wall reflections are the music signal delayed in time, colored in timbre, and spatially positioned at different locations from the direct sound. All these factors can degrade sound quality. Moreover, floor and side-wall reflections interact with the direct sound to further color the music’s tonal character. The figure below shows how the sound at the listening seat is a combi nation of direct and reflected sound.
Side-wall reflections color the music’s tonal balance in three ways. First, virtually all loudspeakers’ off axis responses (frequency response measured at the side of the loudspeaker) are much less flat (accurate) than their on-axis responses. The sound emanating from the loudspeaker sides (the signal that reflects off the side wall) may have large peaks and dips in its frequency response. When this colored signal is reflected from the side wall to the listener, we hear this tonal coloration imposed on the music. Second, the side wall’s acoustic characteristics will further color the reflection. If the wall absorbs high frequencies but not midband energy, the reflection will have even less treble.
Finally, when the direct and reflected sounds combine, the listener hears a combination of the direct sound from the loudspeaker and a slightly delayed version of the sound reflected from the side wall. The result is a phenomenon called comb filtering, a sequence of peaks and notches (hence its similarity to a comb) in the frequency response caused by constructive and destructive interference between the direct and reflected sounds. It all adds up to coloration of the signal at the listening position.
The result of these mechanisms—the loudspeaker’s colored off-axis response, the sidewall’s acoustic properties, and comb filtering—is a sound with a very different tonal balance from that of the direct signal from the loudspeakers. Side-wall reflections are one reason the same loudspeakers sound different in different rooms.
Fortunately, treating side-wall reflections is simple: just put an absorbing or diffusing material on the side walls between the loudspeakers and the listening position. Drapes are highly effective, particularly those with heavy materials and deep folds. The floor reflection is even easier to deal with: carpet or a heavy area rug on the floor will absorb most of the reflection and reduce its detrimental effects.
Diffusion turns the single discrete reflection into many lower-amplitude reflections spread out over time and reflected in different directions (see below). Diffusion can be achieved with specialized acoustic diffusers or with any irregular surface. An open-backed bookcase full of books makes an excellent diffuser, particularly if the books are of different depths, or are arranged with their spines sticking out at different distances.
Note that it isn’t necessary to treat a listening room’s entire side-wall area; the reflections come only from small points along the wall. At mid- and high frequencies, sound waves behave more like rays of light. We can thus trace side-wall reflections to the listening seat and put the absorber (drapes or hanging rug) or diffuser (bookcase or CD racks) in exactly the right location. As with light rays, a sound wave’s angle of incidence equals its angle of reflection. That is, the angle at which a sound wave strikes a reflective surface is the same as the angle at which it bounces off that surface. We can exploit this fact to find the most effective position for the absorber or diffuser. Simply sit in the listening seat and have a friend hold a hand mirror against the sidewall at the level of the speaker’s tweeter. Have him slowly move the mirror toward the back of the room until you see the speaker’s tweeter in the mirror. This point of visual reflection is also the point of acoustic reflection. Repeat the process for the other side wall. If your listening room is symmetrical and the listening position is in the middle of the room, you need use this technique on only one side wall, and then duplicate the acoustic treatment on the other. To maintain acoustical symmetry in the room, both side-wall treatments should be the same.
3) Thick, boomy bass
Thick, boomy bass is a common affliction that can be difficult to control. It often results from room resonance modes, poor loudspeaker or listening-chair placement, poor loudspeakers, or not enough low-frequency absorption in the listening room. As we will see in the later section on standing waves, listening-seat position can also increase bass bloat.
If thick and boomy bass persists even after minimizing it with careful loudspeaker placement (the most effective method of alleviating the problem), you may want to consider different loudspeakers. If, however, the boominess is minor and you want to keep your loudspeakers, you can make the presentation leaner and tighter by adding low-frequency absorbers. These acoustic devices soak up low frequencies rather than reflecting them back into the room. Unlike drapes and bookcases that serve double-duty as conventional domes tic furnishings, low-frequency absorbers are purpose-built acoustical devices that may not aesthetically complement all decors. Nonetheless, adding low-frequency absorption to a listening room often confers a large improvement in the sound quality, specifically bass articulation, dynamics, and midrange clarity. Cleaning up the bass bloat improves the midrange because removing the excess low-frequency energy no longer obscures or intrudes on the midrange. As a result, vocals have greater clarity and openness.
A good example of a low-frequency absorber is the Tube Trap from Acoustic Sciences Corporation. These cylindrical devices are available in a range of sizes from 8” to 16”, with the larger diameter delivering greater absorption at the lowest frequencies. Tube Traps are usually positioned in the corners behind the loudspeakers, which increases their effectiveness.
The Tube Trap is extremely effective in controlling low-frequency room problems. (from Acoustic Sciences Corporation)
You can often tame boomy bass simply by moving the listening seat forward or backward. The sound energy in a room isn’t distributed evenly throughout the room. Instead, stationary patterns of high and low pressure, called standing waves, are set up in the room. Because standing waves occur at low frequencies, a listener in a high-pressure zone (also called a peak) will hear boomy bass. Moving the listening seat forward or backward out of the high-pressure zone will often reduce boomy bass. Conversely, if the sound is excessively thin and lacking bass, you could partially position the listening chair in a high-pressure zone to increase the sense of weight and fullness. Moving the listening chair forward or backward by about two feet is usually enough to affect a change in the bass.
4) Reflective objects near the loudspeaker
Reflective objects near the loudspeakers—equipment racks, windows behind the loud speakers, subwoofers or furniture between the loudspeakers, even power amplifiers on the floor—can cause poor image focus and lack of depth. The best solution is to remove the offending object. If this isn’t possible, move the acoustically reflective object behind the loudspeakers, if possible.
There’s an obvious conflict here for those of you whose audio system is used for both music and home theater; you will likely have a big piece of glass—a television—between your left and right speakers. The solution is to pull the left and right speakers forward of the television by a few inches so that the left, center, and right speakers create an arc. (This technique is described in more detail in Section 10).
Acoustical Do’s and Don’ts
We’ve summarized this section into a few simple guidelines for improving your listening room. If you just want some practical tips for getting the most out of your system, this is the section to read. More detail on each of these points can be found throughout the section.
1) Loudspeaker placement
Just as real estate agents chant “location, location, location” as the three most important things about the desirability of a house, the three most important ways to improve the sound in your room are loudspeaker placement, loudspeaker placement, and loud speaker placement. Follow the suggestions in this section and spend a few hours moving your loudspeakers around and listening. You’ll not only end up with better sound, but become more attuned to sonic differences. All acoustic treatments should be built on a foundation of good loudspeaker placement.
2) Avoid untreated parallel surfaces
If you’ve got bare walls facing each other, you’ll have flutter echo. Kill the flutter echo by facing one wall with an absorbent or diffusive material such as drapes, bookcases, or media-storage racks. Dedicated acoustical products work well.
3) Absorb or diffuse side-wall and floor reflections
Bare floors should be covered with carpet between the listening seat and the loud speakers. Treat the side walls between the loudspeakers and the listening position with an absorbing or diffusing material. Avoid having reflective surfaces, such as bare walls and windows, next to the loudspeakers.
4) Keep reflective objects away from loudspeakers
Equipment racks, power amplifiers, furniture, and other acoustically reflective objects near the loudspeakers will degrade imaging and soundstaging. Move them behind the loudspeakers if possible.
5) Move the listening seat for best low-frequency balance
Standing waves create stationary areas of high and low pressure in the room. Move the listening chair for best balance. Avoid sitting against the rear wall; the sound will be bass-heavy.
6) Break up standing-wave patterns with irregular surfaces or object.
Strategically placed furniture or structures help break up standing waves. Large pieces of furniture behind the listening position diffuse waves reflected from the wall behind the listener.
Digital Room Correction
We’ve seen in this section that the listening room is a crucial link in the music playback chain. Every listening room, no matter how good, radically alters the sound produced by a pair of speakers. The room acts as an equalizer, boosting some frequencies and attenuating others. This change in frequency response can be as much as 30dB in the bass, adding large amounts of coloration to the music. Moreover, the room briefly stores and releases energy at certain frequencies, causing some bass notes to “hang” in the room longer. The result is a thickness and lack of clarity in the bass, along with a reduced sense of dynamic drive.
It’s been said that a loudspeaker designer has l00% control over his product’s sound above 700Hz, 50% control from 300Hz to 700Hz, and only 20% control below 300Hz. This aphorism reflects the increasing influence of the listening room on sound quality at lower and lower frequencies.
Although the listening room imposes far more severe colorations than any electronic component, we’ve grown to accept this musical degradation as an inevitable part of music listening. Even custom-built, acoustically designed rooms housing perfectly positioned loudspeakers will introduce significant colorations. All rooms intro duce colorations: the better ones simply do less damage.
Attempts to reduce room-induced colorations with analog equalizers have met with limited success. Analog equalizers add their own audible problems, and are limited in resolution. Digital equalizers can have greater resolution than analog ones, but are still a crude tool for dealing with room problems.
The advent of Digital Signal Processing (DSP) provides a powerful new opportunity to remove the effects of the listening room on reproduced music. DSP is the manipulation of audio signals by performing mathematical calculations on the numbers that represent the music. DSP chips can be programmed to perform as filters or equalizers with many hundreds of frequency bands, and with characteristics impossible to realize with analog equalizers. The trick is putting this advanced technology to work to surgically correct room-induced colorations.
Far more sophisticated than a digital equalizer, a DSP room-correction system analyzes the response of your loudspeaker/room combination with high resolution, then creates digital filters to remove the room-induced problems. The room-correction system not only removes the room’s effects, but also corrects for speaker colorations. If your speakers have a peak of energy at 2kHz, for example, the room-correction system can remove this coloration. In addition, the room-correction system will make the speaker/room response identical for each speaker. This new technology removes the room’s effects on reproduced sound ‘electronical’ before it is reproduced by the loudspeakers. Put another way, the room-correction system distorts the signal in a way that counteracts the distortion imposed by the listening room. The result is flat response at the listening position.
Note that because room-correction systems operate in the digital domain, analog signals (from LP, FM, portable music player) must be digitized, then converted back to analog. That’s why most room-correction systems include an integral analog- to-digital converter. Digital signals, such as from a CD transport, are input directly to the room-correction system, which either converts that digital signal to analog for driving a power amplifier, or outputs a digital signal for conversion to analog with an out board digital processor. Although room correction can produce profound improvements in bass quality and image focus, some audiophiles will be reluctant to digitize LPs. Analog-to-digital conversion and digital-to-analog conversion are not sonically transparent, although today’s converters are much better sounding than those of just a few years ago.
Room-correction systems are rare because the complexity of hardware and soft ware requires a huge expenditure in development time and money. Make no mistake: correcting a room’s response is an extraordinarily difficult task. Moreover, a room-correction system is as much a computer as an audio product, requiring specialized design skills not normally found among audio engineers. The first room-correction systems were difficult to set-up and dial in correctly; more modern examples are much easier to use.
A new generation of room-correction systems, however, is much easier to use, doesn’t require a computer or computer skills, and is significantly more effective than were the first models. Such a product is shown in below.
Today’s room-correction systems are much easier to use and more effective than earlier-generation models. (e.g., gear from Lyngdorf Audio)
My experience with room correction suggests that the technology is extremely effective in removing colorations and restoring clarity to reproduced music. With room correction, the sound has a “lightness,” agility, and clarity that are impossible to achieve in any other way. The overall presentation seems to have less midbass boxiness, and extreme low frequencies have greater dynamic impact. In addition, soundstaging improves because identical response from both loudspeakers is essential to precise image focus. (That’s why each speaker must be toed-in by exactly the same amount.) Without room correction, image size and placement can change as an instrument moves between musical registers because the response of each speaker/room is different. With identical output from each speaker, image focus becomes tighter and the soundstage is better delineated. Once you get used to the sound of a system with DSP correction, it’s hard to back.
Accessories and Cable Dressing
There are many setup techniques and accessory products whose individual audible differences may be very small, but that can increase a system’s performance when combined. Taking your system to the next level of performance with these products and techniques requires patience, listening skill, and a desire to extract the last bit of performance from your system. There’s nothing more satisfying than realizing a significant audible improvement without spending a dime.
All system setup should be based on a foundation of good loudspeaker placement. Once you’ve made this coarse adjustment, you can work on refinements. As your system’s sound improves, you’ll become more attuned to small performance variations.
How the cables behind your equipment rack are routed can affect the sound. Keep AC cords away from signal-carrying cables. If they must meet, position them at right angles to each other rather than running them parallel to each other. AC cables radiate 60Hz hum that could be picked up by signal cables. Cables carrying digital data—the output from a CD transport, a DVD player, or other digital source—should be kept away from both AC cables and analog signal-carrying cables. Cables carrying digital data radiate noise that could get into the analog signal.
When playing analog sources, turn off all digital components. Again, digital signals radiate noise. Some A/V controllers automatically shut down unneeded digital circuits when the controller’s source-selection switch is set to an analog input.
If you have a power amplifier (or integrated amplifier) in your equipment rack, keep it as far as possible from a phono preamplifier (if your system uses one).
Provide adequate ventilation for heat-producing components. Don’t stack a CD player on top of an integrated amplifier, for example. If you must stack components on a single rack shelf separate them with cones or feet. Overheating may degrade performance, and will certainly shorten product life.
Experiment with isolation feet or cones between your components and the equipment rack. Some are more effective than others, so it’s best to try them in your system before purchasing. Most dealers and mail-order suppliers will allow you to trade in feet and cones if they don’t improve your system’s sound.
Keep interconnects and loudspeaker cables as short as possible. All cable degrades the audio signal; the less of it in your system the better.
Ensure a good contact between the loudspeaker cables and binding posts. Use a nut-driver to get a tight fit, being careful not to over-tighten. Periodically clean the binding post contacts and the speaker cable’s spade lugs or banana plugs with a contact cleaner such as Caig DeoxIT. Similarly, clean the RCA jacks on your equipment and the RCA plugs on your interconnects.