| Cinema Cynergy January 2001
Speaker Placement
Where do I put all those speakers?
The dilemma with home theater speaker placement is that we
can discuss the ideal positioning of speakers in a "typical" room all day long,
but most of us must also use these rooms for purposes other than home theater. Thus,
placement without regard to other factors is usually not possible. Considerations such as
the location of furniture, aesthetics, and the acoustics of the room are important factors
in determining the final positioning of speakers. Compounding the problem is the fact that
home-theater systems typically require six speakers or more (including a subwoofer), which
can take up quite a bit of space that you may not necessarily have to spare.
Living in a perfect world: ideal speaker placement
Let us first discuss the ideal placement of speakers in a
home-theater system assuming that we have an empty room to work with. This will allow the
speakers to be positioned anywhere that we wish. The most basic tenet of the placement of
home-theater speakers is that they must all be symmetrically placed in relation to the
seating position (except for the single subwoofer). By this, we mean that each speaker
must be placed equidistant from the seating position and at equal and opposite angles to
any speaker that it may be paired with.
To achieve this equivalence in distance to the listener,
the center channel must be set back slightly from the left and right fronts. It should
also be positioned either directly above or below the television monitor, with both
situated exactly the same distance from the left and right front speakers. The tweeters
for the three front speakers should all be positioned at the same height and the left and
right fronts should each be the same distance from the side and front walls. Most main
speakers also require room to "breathe" and as such should not be placed
directly against walls, the sides of the television, or placed inside cabinets etc.
The surround speakers can be placed either behind or to the
sides of the seating position, and preferably slightly above ear level. If the speakers
are placed behind the listener and on a wall, the seats should be moved away from the wall
so that the speakers are not too close to the listener. If the surround speakers are
placed immediately to the sides of the seating position, they should be angled so that
they do not fire directly into the ears of the listeners from either side.
Ideal speaker placement for a home-theater system showing both
rear wall and side wall positioning of surround speakers.
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The only exception to these rules is for the subwoofer.
Because there is usually only one subwoofer in a home-theater system, there is no choice
but to place it in a position that is not symmetric with the other speakers. Subwoofer
placement is dictated more by room interactions that affect frequency response, not
imaging issues, which are the main concern with the other speakers.
If the speakers for a home-theater system were placed in a
room with consideration only for acoustics and no other factors, their placement might
look something like what's in the diagram on the right.
Living in a world full of compromise: real world speaker
placement
The first compromise that usually has to be made when
positioning speakers for a home-theater system is that they cannot all be situated the
same distance from the seating position. However, this can be remedied with the use of the
delay settings that are present on all receivers and processors. With these settings,
differences in the distances to the listening position from the mains, center, and
surrounds can be compensated for. However, it is best to try and keep the distances from
each speaker to the listening position as equal as possible.
If the center speaker is placed atop the television monitor
as it most often is, it will probably be slightly above the vertical plane of the left and
right speakers. Tilting the speaker downwards will help compensate for this difference in
height as will tilting it up if it is situated below the mains. Also, place the center
speaker as close to the front edge of the television as possible to avoid having sound
reflect off of the television’s cabinet. Finally, orient the center speaker the way
it was intended (i.e. do not flip it on its side), or it will not image properly.
As previously mentioned, the front speakers (including the
center channel) must be placed symmetrically around the television monitor, otherwise the
sound will not image correctly across the front of the room. This is the most crucial rule
of surround-sound speaker placement as most of the action and imaging occurs in the three
front speakers. Placing the mains the same distance from the side and rear walls is not as
critical as making sure that all three front speakers are placed symmetrically around the
television. The left and right fronts can also be "toed-in" if required to
achieve better imaging. Note that fine-tuning and calibration of home-theater systems will
be covered in more depth in a future column.
The positioning of the surround speakers is usually the
most problematic due to the architectural limitations of most rooms. The two most common
difficulties are that the seating position is too close to the rear wall if the speakers
are to be placed there, or the lack of appropriate side walls for placement to the sides
of the listener. Typically, surround speakers should be mounted slightly above ear level,
but otherwise their placement can be very flexible.
There are basically two very different designs of surround
speakers utilized by most manufacturers: dipolar or bipolar speakers which radiate sound
in two directions, and direct-radiating designs which radiate sound in only one direction.
Dipolar and bipolar surrounds are designed so that they will not radiate sound directly at
the listener and are most often placed on the side walls. However, they can still be
placed on the rear wall to good effect. Direct-radiating surround speakers should
generally be pointed towards the listener, but should not be aimed directly at the
listeners from the sides or the rear. Direct-radiating surrounds usually give the best
results when angled slightly into the room or directed gently towards the listening
position.
There is also a balance that needs to be struck between
good surround envelopment that requires a diffuse soundfield and the more pinpoint imaging
required to locate stereo surround effects. For example, if you prefer a very enveloping
rear soundfield, you might consider aiming the speakers towards the rear wall or even
pointing them up at the ceiling or other such object to provide more reflected than direct
sound. For more precise imaging, the surround speakers could be placed behind and to the
sides of the seating position and then angled towards the listener. Because of all these
considerations, judicious experimentation is called for when determining the placement of
surround speakers.
Very low bass is non-directional, so the subwoofer can be
placed wherever it performs best. However, the more output that a sub has and the higher
the frequencies that it reproduces, the more localizable that it will become. Something to
keep in mind is that placing a subwoofer close to room boundaries (walls and corners) will
reinforce the output, but may make it sound boomy and less accurate. Moving a subwoofer
away from room boundaries will make the bass tighter and more articulate, but will reduce
its output. Depending on how the subwoofer interacts with the room due to its positioning
and orientation, certain frequencies may also be enhanced while others are diminished. A
sub will usually sound okay just about anywhere you put it, but some experimentation will
help you find the best location where it is not too localizable and still has solid bass
that is not boomy.
Final Thoughts
Positioning each of the speakers in a home-theater system
requires that you follow a few simple rules and perform a whole lot of experimentation.
Use the concepts illustrated in the discussion of ideal placement as a starting point and
do not be afraid to try different positions for your speakers (especially the surrounds
and subwoofer) to get the sound that best suits your tastes. A little work on your part to
optimize the placement of your speakers will result in enhancing the enjoyment that you
get from your home-theater investment.
...Roger Kanno
roger@hometheatersound.com |
