There could be (and likely is) undreamed of performance lurking within your system, just waiting to be tapped! What's that you say, better sound than I have now? Most likely, yes. While some of you have been fastidious in your approach to speaker placement, the plain truth is that most of us do not know how (or do not take the time) to properly position our loudspeakers. I hope to help alleviate this situation with the information that follows.
To preface, let me say that an article on "correct" speaker placement may be impossible to write. That is because every situation (and, to a certain extent, every speaker) requires a different approach to optimization. Further, one's personal preference may suggest a departure from the norm. Fortunately, there are some helpful guidelines that we can use to aid us in our quest for the perfect sound.
The home environment presents a multitude of problems/considerations in choosing a location for our speakers. Room layout, furniture, esthetics, accessibility by children and pets, and, not to mention our sometimes contrary domestic cohabitant(s)! The ubiquitous Wife Appeal Factor (WAF) is often an important gauge in making a decision. To keep things simple, we will concentrate upon the ideal, and assume you have unlimited freedom. Please alter the suggestions to conform to your situation.
To better understand the terminology and the reasoning behind the recommendations, let us first explore a few basics of acoustic theory (an oversimplification here, just a few distilled points for purpose of illustration).
The listening room affects the sound of a speaker due to standing waves (at frequencies dependant on room dimensions) and by the reflections created within. Some frequencies will be reinforced, others suppressed, thus altering the character of the sound. If we were to listen to our speakers outdoors (or inside an anechoic chamber), much of the coloration we’ve been used to hearing would disappear. This is a major reason loudspeaker designers test their creations in such an environment, not wanting their design decisions or publishes specifications to be influenced by the colorations of any given room. The real world, however, requires that our speakers co-occupy our living quarters, therefore we must deal with the room as a significant contributing factor.
In any listening environment, what we hear is a result of a mixture of both the direct and reflected sounds. Direct sound travels straight to our ears from the speakers. Reflected sounds are many, bouncing off most any hard surface and reaching our ears after the direct sound. In general, the direct sound from the speakers is primarily responsible for the image, while the reflected sounds contribute most to the tonality of the speaker (richness, leanness, etc) and an overall sense of ambience. Any boundary surface (back wall, sidewall, floor) can cause a reflection, and all need to be considered during placement. The trick is to place the speaker (and/or treat the room) in a location that will take advantage of the desirable diffused reflections while diminishing the unwanted hard reflections.
On to specifics.
Distance to the Listener:
For proper imaging to take place, sound from each speaker must arrive at the listening position at precisely the same moment. This requires that the speakers be exactly the same distance away from the main seating position. We're talking about precision here. A difference of less than 1/4" will be easily audible in better systems to careful listeners.
Far and away, the very best way to ensure accuracy is to use a laser distance measurer. This tool is ideal for the task and will give you extremely precise readings. You'll find the laser measurer is also an invaluable aid in setting toe-in.
Set up a “target” at the listening position with the goal of locating it precisely at ear level. We use a blank piece of cardboard taped to a microphone stand placed slightly behind the listening chair. Alternately, this could be a blank sheet of paper taped to a point on the listening chair. This step establishes a reference point to use for all your measurements when using a laser.
From a reference point on each speaker (I like to use a spot near the tweeter), use the laser to measure the distance to the target from each speaker with your goal being no more than 1/4” difference in distance. Making this measurement will also get you started on toe-in alignment.
Lacking a laser measurer, a tape measure may be used though it can be challenging to achieve accurate readings. Similarly, a string can be employed and can be a helpful adjunct to your tape measure.
Tape a string to the listening chair's midpoint, trying for a spot as close to ear level as possible. Now, unroll enough string to reach a speaker, then pull the string taught at a reference point on the speaker. Grasp that point on the string with your thumb and forefinger, then walk to the other speaker and compare. Adjust positioning until each speaker is at precisely the same distance.
Distance to Sidewall and Back Wall:
There are two acoustic characteristics we're dealing with here: bass and soundstage. It's well known that the closer a speaker is to a boundary (wall, floor, ceiling) the more bass reinforcement. Changing the location in relation to these surfaces will dramatically affect both the quality and quantity of the bass. Note: moving the listening position can have as much effect on bass as moving the speaker. The speakers excite room modes that create low frequency standing waves. Because of their long wavelengths, these waves are present regardless of where the speakers are located. Moving the listening position, however, determines whether that point is in relation to areas of additive or subtractive bass pressure. If you have the option, try moving the listening chair a foot or two in each direction to find the optimal position.
With regard to soundstaging, you'll find that depth is dramatically influenced by rear wall proximity. Increasing the distance from the speaker to the wall behind will increase soundstage depth. However, pulling the speaker too far out may degrade focus. In most cases, room layout dictates the maximum distance the speakers will be allowed to intrude into the listening space, but experiment to as a great degree as possible.
Most speakers need to be a minimum of a foot or two away from the side and back walls to reduce early reflections (early reflections reach the listener out of step with the direct sounds, causing image degradation). Distance to reflective surfaces, speaker radiation patterns, and toe-in all contribute to the amount and intensity of early reflections. Minimizing these reflections is key to maximizing soundstage and focus. Beyond the scope of this article, check out Room Acoustics for a more in-depth look at early reflections and how they can be controlled using acoustic products from Acoustic Sciences and RPG.
Differences among speakers can also influence positioning. A planar, for instance (which radiates sound both front and back with null points to the sides - a figure-of-eight pattern), may be less critical of a nearby sidewall, but very critical of the distance to the back wall. Just the reverse is true for many dynamic designs whose propagation pattern is mainly to the front, with some to the sides and little to the rear (cardioid pattern).
You'll find that the side wall distance will affect both soundstaging and tonal balance. In general, proximity to the sidewall will more influence midrange balance while the distance to the back wall will have more impact on bass.
It is most important to ensure that the distance to the back and side walls are unequal. Do not place the speaker, say, 20" from both back and side walls. That said, be sure both speakers are set the same; symmetry is very important. By that we mean if the left speaker is 20" from the back wall and 30" from the side-wall, try to place the right speaker in the same way. This may not be possible in all situations, but do your best to give each speaker a similar acoustic environment.
Distance Between the Speakers:
This will be determined by the distance to your listening position, the particular speaker you own, and, to a great measure, your own personal preference. I generally prefer to start with an equilateral triangle, the apex of which is located at the listening position, and the two speakers forming the baseline (here, speakers placed 6' apart would suggest a listening position 6' away), and experiment to produce the best soundstage. Note: Some manufacturers recommend a specific measure for speaker separation. Use this measurement, if available, and your room permits, but remember that any recommendation is only a starting point. You'll find that increasing the distance between the speakers will widen the soundstage (until at some point the center image falls apart), decreasing the width will narrow the stage and increase center focus. As mentioned previously, this is partly subjective. I listen to a lot of female voices and a strong center focus is really important to me. You may concentrate on orchestral works and prefer a wider stage and be willing to sacrifice some specificity of image for the extra bloom. Select recordings with which you are very familiar. My personal preference is toward simple recordings with good, even spread across the stage, and a strongly focused center image.
As discussed previously, the distance to the side walls affects (mainly midrange) tonal balance. As we move the speakers closer or further apart, the relationship to the side walls change. Further, the proximity of one speaker to the other will influence tonality as well.
Toe-in depends on three factors: the particular speaker you have chosen, the room, and your personal preference. Some speakers sound best with little or no toe-in, others may require a great deal to perform properly. Follow the manufacturer's recommendations or, lacking those, start with no toe-in and begin turning the speaker inward (pointing more toward the listener) until the right amount of center-fill is obtained, without sacrificing soundstage width.
You can use the "string method" described in calibrating the distance to each speaker, but this time measuring to both the inside and outside corners of each speaker. However, far and away the best method for setting toe-in employs a laser pointer. You'll need a "target" for the laser, ideally something positioned at ear level. a pillow propped up in the listening chair or a point on the wall behind the listener can be used as reference points. Simply place the pointer on top of the speaker, making certain it's square to the front of the enclosure, and adjust toe-in until the laser focuses at exactly the same point on your target.
Adjust the position of the target itself to correlate with the speaker manufacturer's recommendation for where the speaker output should intersect. Speakers requiring a large amount of toe-in will intersect at or just behind the listener, that point moves further back when less toe-in is indicated. Some manufacturers are adamant regarding the amount of toe-in, others are less specific in their recommendations. In general, more toe-in increases center focus, but reducing stage width. Less toe-in widens the stage, but center focus will be sacrificed if you go too far. Sometimes it's a balancing act based on the room, the speaker, and the preference of the listener.
Note: Toe-in and distance between the speakers are often interrelated. You may find that it will be necessary to revisit the distance between your speakers after you have experimented with toe-in.
Tilt, (fore and aft) also can be very important in influencing the sound of a speaker. Although most speakers today should be level, some designs recommend specific tilt (generally rearward) for proper imaging. I recommend starting level, and experimenting rearward from there, if necessary. It's very rare that tilting the speaker forward will be of use. Use a carpenters level for accuracy, and remember to check both front-to-back and side-to-side.
Every speaker has been designed with a specific listening height in mind. Generally speaking, your ears should be on axis with a point midway between the tweeter and woofer (two-way) or tweeter and midrange (3 way). Again, consult the manual for specific recommendations.