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Do-it-yourself
Speaker Placement
You wouldn't dream of watching a feature length film without sound. And the sound set-up to maximize
the auditory experience will give you the most enjoyment. The best speakers can sound terrible if
improperly placed. Conversely, you can make a notable difference in the performance of modest speakers
by proper speaker placement at minimal expense other than time. It will require some intensive listening
and some tinkering, but you're sure to find the result worthwhile.
You could use some electronic test equipment such as a spectrum
analyzer to do the analysis; however, using your ears as your analyzer
will give you excellent "do-it-yourself" acoustic skills that are inexpensive yet very rewarding.
You could also add acoustic treatment to your room, and we'll deal with these later, but first we need to
optimize the speaker positions in your room. I can't emphasize this enough that this is the single most
important task you can accomplish to improve your system’s performance.
Setting up your front speakers
I'll start with stereo speakers, first for solitary music listening, but next as the basis for enjoyable
movie watching. Many will argue that a home theatre set-up is not suitable for music listening. We'll not
address that argument here, but simply say that most of us have a single multi-functional room for our
entertainment centre where we both listen to music and watch movies. We'll address this multi-functional use.
You should first familiarize yourself with the front speakers you are going to use.
Look at the manufacturer's frequency response charts. These are
anechoic measurements which will change as soon as you put your speaker in a room with walls and a ceiling;
however, the response charts will indicate what the speaker’s limitations and capabilities are. The room's
reflective characteristics will change the bass response significantly. Bass response will increase should
you place a full range speaker against a wall or in a corner. But a bookshelf speaker's response can roll
off dramatically below 125Hz; so, deep bass problems are less an issue when positioning them. Using a wall or
corner may even be beneficial. The manufacturer may recommend the position for proper phase alignment which
for some might be directly aligned with the tweeter, or for other speakers, it could be a point between the
woofer and tweeter. When positioning your speakers and listening position, your ear level should be in a
relatively horizontal plain (perpendicular to the face of the speaker) with this proper phase alignment position.
Ideally, a listening room can be designed and built with dimensions that are favourable
to the task of minimizing sound distortion. In reality, many of us have to work with an existing room. I'll
assume a common rectangular room shape for this exercise, asking you to note that an L- shaped room will
behave slightly differently, and require some other considerations. First you should determine on which wall
your speakers will optimally be placed. If your room is square, it doesn't matter. If your room is
rectangular, the room dimensions will affect whether a short or a long wall is best, but there is no neat
formula for this. The answer isn't simple without the use of an analyzer, but with some manual effort you
can make a tremendous difference in the optimum choice. The speaker distance from the front and sidewalls will
also dictate the listening position. There are a number of interactive factors; so, be patient and prepared to
move some furniture. Hopefully, other family members will be supportive!
Figure 1 illustrates a measured approach to quickly placing stereo speakers in an approximate position which
should be close to an optimum position. From here, the procedure outlined below will tweak the positioning
for enhanced performance.
To determine which wall to use, place one speaker on each wall. Position the speakers at
listening position ear height where your left or right stereo speaker would typically be placed. Use figure 1
above if unsure. Play a mono signal from your CD player to one speaker at a time paying particular
attention to the bass. Alternatively, the AVIA Guide to Home Theater DVD has numerous audio test tones to help
you here. Keep yourself centered between the sidewalls, and move forward and back six inches at a time. Your
distance from the speaker will play a part in the frequency response. You should also move the speaker forward
and back, and side to side, six inches at a time in this process. You're looking for for which speaker has the
flattest bass response. Not more bass, but even, flat bass. Listen for smooth and connected bass from the
mid-band down to lowest frequencies. Once you're satisfied you've found the proper wall, you've also found the
proper speaker and listening position as well. Mark it for reference with masking tape on the floor.
Now you can match up a front pair of speakers on the best wall. Note that you should place each speaker equidistant
from the sidewalls and the distance each speaker is placed from the front wall should be equal (but different
from the distance to the side wall). Should they not be symetrically placed, each speaker will have a different
frequency response and the depth-of- field of the soundstage will collapse and the imaging will be off-centre.
Here's why.
In a 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. Many reflected sounds bounce off reflective surfaces
and reach our ears after the direct sound. These direct and reflected sounds interact, sometimes reinforcing one
another, sometimes canceling each other depending on their relative phase relationships at the time of
interaction. The time delay, and thus the frequency of interaction, is dependent on the speaker distance from
the walls. If the left and right speakers are different distances from the walls, the cancellations will occur at different
frequencies confusing our hearing.
A variation on this first positioning method will fine tune the distance from the sidewall. Measure the distance
from a speaker to the listener. Mark a point that is half of this distance directly behind the listener. So if
the speakers are 8 feet from the listener, mark a point 4 feet behind the listener. Aim the speaker at this point
at all times while finding the distance the speaker should be from the side wall. Move the speakers apart slightly.
Vocals, particularly female, work very well here. Listen to the vocal; it should be well defined between the
speakers. As you move the speakers apart the vocal will become less defined, and ultimately will sound like it is
coming from two separate speakers rather than a point in between. When this occurs you have moved the speakers
too far apart and should move them in slightly.
Toe-in (the amount of angle the speaker is turned toward the listener) depends on three factors: the loudspeaker
characteristics, the room and your personal preference. Some speakers require little toe-in while others may
require substantial adjustment to sound best. 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 proper
amount of centre-fill is obtained, without sacrificing soundstage width. In general, the closer the speakers
are together the less they should be angled in.
Centre Channel
The objective of speaker positioning is like they say about real estate "location, location, location".
We're talking about sound here. A clear and consistent soundstage across the front supported by ambience
to the side and back. That's why we're starting with the front of the listening room, getting the soundstage
set with the left and right front speakers, and then positioning the centre speaker which carries much of the sound in a movie,
especially dialogue. A common problem encountered with the centre speaker is that it is often set too loud and may be too far forward.
Although the newer receivers can correct for this to a degree, it's best to let the natural placement of the speakers allow for less
electronic processing. If set on a shelf or above a CRT TV place the
front of the speaker in line with the edge of the shelf or TV. This
will minimize any distortion of the sound which might otherwise be
shaped by the furniture.
Once more -- location is the key. A good recording coupled with a good sound playback system will allow you to
clearly identify various sound sources in front of you consistently across the soundstage from one side of the room
to the other.
If a major task of the centre speaker is to place dialogue in the middle of the screen
(make it sound like it
is coming from the actor's mouth) then, when using a large 50" or 65" screen, why not use 2 centre speakers,
for example, above and below the screen? The problem with this 2 speaker scenerio is that there is a significant
risk that an interfering wave pattern will occur between speakers that will muddy the sound. If possible, it is best
to have just one centre channel speaker well placed.
Try to place the speaker as close to ear level as possible, centred preferably just above or below the viewing screen
as close to the screen as possible without causing visual interference or electro-magnetic interference with the TV.
Most centre speakers are shielded to prevent this interference. If you must place the speaker near the floor or
ceiling, use some noise absorbent material to absorb reflections from the speaker.
Many centre channel speakers do not have full range capability (missing deep bass response). When using this
type of speaker, place the speaker the same distance away from the listener as the main front speakers. However, if
using a full range speaker whose bass will be emphasized if placed too close to a wall, locate it the same distance
from the wall as the main speakers.
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Surround speakers play different roles depending on
the material and its channel processing. For
example, Dolby Pro-logic carries the same monophonic
information in each of the 2 surround speakers. The
ambience created is a front-to-back sound flow
rather than side-to-side. A muted ambience and depth
is created. Dolby Digital adds the capability
of side-to-side motion with discrete sound from each
speaker. Because movie watching is commonly a
social event, with listeners often positioned
outside the "sweet spot", a diffuse sound
pattern from the surround speakers is typically
created, with less emphasis on localization such as
might be expected when listening to music.
Your typical use will determine your choice to
sacrifice pinpoint localization for the preferred
diffusion of movie surround or to lean more to
precise localization for music listening.
With a 5.1 channel system, speaker location is typically 1 or 2 feet behind
the seating area and about 2 feet above the ear
level. With a narrow room, the speakers can be
mounted on the side walls, whereas a wider room may
require floor or ceiling mounted stands.
With 6.1 or 7.1 channel systems, the main
surrounds are place in a similar manner to a 5.1
system. The additional back centre speakers are typically mounted on the back wall or on floor or
ceiling mounted stands if the back wall is too far
away from the listening area. As with the side
surrounds, these speakers should be above ear
height. A good guide to placement is at an angle
from the listening position (center speaker at 0
degrees) of 135 to 150 degrees.
Subwoofer
Subwoofer placement is often guided by 2 issues:
1. The visual acceptance of such a large speaker,
although many are now being designed to appear like
a well-styled piece of furniture.
2. The fact that bass sounds less than about 80Hz are less likely to be
identified as coming from a particular location
(omni-directional) and
corner placement tends to emphasize the bass.
Because of reflections coming off walls tending
to either peak or null at cross points, a corner
placement may sound great from one seating position
while quite weak in another. Moving the
subwoofer slightly in one direction or another may
help to maximize smooth and even bass effect from all
seating positions. Likewise, if the bass is
too strong or "boomy" for your taste, you may wish to pull it
farther away from the corner or a wall, where there
may be a tendancy to overemphasize a particular
range of frequencies. Which corner
or where in the room the subwoofer is placed isn't
as critical as it is for other speaker types due to
the non-localization of lower frequencies.
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