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Speaker Placement
There could be 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 departure from the
norm. Fortunately, there are some helpful guidelines that
we can use to aid us in our quest for perfect sound.
The home environment presents a multitude of problems/considerations
in choosing a location for our speakers. Room layout, furniture,
aesthetics, accessibility by children and pets and, not
to mention our sometimes contrary domestic cohabitant(s)!
The ubiquitous Wife Appeal Factor (WAF) has become a most 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.
The Room room affects the sound of a speaker by the reflections
it causes. 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 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 speaker diaphragms.
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 are primarily responsible
for the image, while the reflected sounds contribute most
to the tonality of the speaker (richness, leanness etc).
Any boundary surface (back wall, side wall, 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 of advantage of the desirable
reflections while diminishing the unwanted 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. Difference
of less than ¼" will be audible in better systems to careful
listeners.
Using a tape measure for this procedure can be
cumbersome, so I like to use a string. It's easy and very accurate. Simply tape
a string to the midpoint of the listening chair, trying for
a spot as close to ear level as possible. Now, unroll enough
string to reach one of the speakers, then pull the string
taught to a reference point on the speaker, I like to use
the tweeter. Grasp that point on the string with your thumb
and forefinger, then walk to the other speaker to see how it
compares. Simply adjust the distance until each speaker is
exactly the same distance.
Just to make things more confusing
for you, I will add that there are times you may want the
speakers to be at slightly different distances from the
listener. This is mainly true when trying to compensate for
a level imbalance cause by room acoustics or placement
limitations. I always begin with the two speakers precisely
the same distance, and change that only if absolutely
mandatory.
Distance to side wall 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 affect on bass as moving the speaker. The
speakers excite room modes which 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 with 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 regards 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 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 pattern 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 then 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 side
wall, 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 (cardiod 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 insure 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 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 base line (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 voice and a strong center focus is really
important to me. You may concentrate of 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 manufacturers 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.
Listening Height. 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.
Summation
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Experimentation is the key to optimum results. Trial
and error will tell you a great deal about how the speaker
reacts in your environment and help you to better balance
strengths and weaknesses of each position you try.
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The goal in determining the position in the room is
to excite as few of the standing waves as possible.
A number of sources have suggested formulas to find
rough placement. Here a couple I’ve seen. Where
x is the distance from the side wall to the center of
the speaker and y is the distance from the back wall
to the center of the woofer. 1) x =
(0.277) x (room width), y = (0.450) x (room width). If
this puts the speakers too far out into the listening
room use x = (0.277) x room width, y = (0.353) x room
width. 2) x = (0.276) x (room width),
y = (0.618) x (ceiling height).
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Once you have found a rough position, place two
pieces of masking tape on the floor, one
marking distance to back wall, another
noting positing from the side wall. Mark the tape in one-inch increments. This
will allow you to move each speaker exactly the same
amount, without having to re-measure each time.
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Exact distances are critical! Always use a tape measure,
half an inch can make all the difference in the world.
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Bear in mind that the best location
for creating a spacious soundstage, may not be the ideal
location for bass. We are searching for a balance, a
compromise of parameters that comes closest to our personal
definition of ideal.
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When setting up new speakers, don’t rush through
the process. Take your time and slowly find the ideal
location over a few weeks of listening. Pressing to
find the right position can be very frustrating. Also
note that the sound of the speakers will change during
break-in. Play the speakers for at least 100 hours
before fine tuning placement.
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If you’ve already placed your speakers, but did
not put much effort into the process, spend some time
tweaking your speaker set-up. I think you’ll be
very pleased with the results.
Additional resources:
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