The following is from Genelec, makers of fine studio monitors
at genelec.com:
PLACING FREE-STANDING CONTROL ROOM MONITORS
THE BAFFLE EFFECT
An enclosed dynamic loudspeaker drive unit has theoretically ideal
working conditions only if its frontal radiation space is either a
full or a half space (i.e. spherical or hemi-spherical radiation).
In practice the radiation angle decreases as the frequency increases
first because of the finite size of the front baffle of the speaker
cabinet and secondly because of the size of the drive unit itself.
For a medium sized speaker cabinet having front baffle dimensions
of 300 x 500 mm the loading of the drive unit will change from full
space characteristics to half space characteristics between
frequencies 200...600 Hz. The level of the sound will increase by
6 dB above this threshold frequency, and the loudspeaker then
predominantly radiates towards the front instead of radiating
omnidirectionally.
If the speaker is placed near a wall, the wall presents an extension
of the baffle of the loudspeaker at low frequencies, and this step
change in the radiated level decreases.
Usually near field monitors are designed to radiate correctly in free
field. The step change described above is compensated for in the
design of the speaker. If this speaker, then, is placed near a boundary,
it's frequency response will be modified, and we experience a bass
boost. The Genelec monitors have versatile room response controls to
take care of these changes.
WALL REFLECTIONS INTERFERE WITH THE DIRECT SOUND
A free standing speaker is usually surrounded by boundaries that
generate reflections(walls, the ceiling and the floor). These boundaries
act as acoustical mirrors to the speaker's radiation, enhancing or
cancelling the direct sound, depending on the phase difference
between the reflection and the direct sound at the listening position.
The problems of boundary refelections diminish as the frequency
increases. This is because the directivity of a conventional loudspeaker
increases with frequency. This is why the boundary reflections mostly
cause problems at low frequencies.
The most common problem at low frequencies is the interference
between the speaker's direct radiation and the reflection from the wall
behind the speaker. At low frequencies this reflection is in phase with
the direct sound. The phase of the reflected sound lags more as the
frequency increases.
Finally, at some frequency the reflection will be delayed so much as to
be in opposite phase relative to the direct sound. Depending on the
relative amplitudes of the direct and reflected sounds, a cancellation
dip (typically 6...20 dB deep) will occur in the frequency response
To overcome this problem we can position the speakers far enough
from the wall to move the first order interference dip below the lower
cut-off frequency of the speaker. To move the dip down to 30 Hz,
the distance needed is 2.8 meters.
Note that when you have a stereo pair, they must have exactly
similar frequency responses to produce exact and accurate stereo
imaging. The boundary reflections change the frequency responses of
the speakers differently if they are at a different distance from the
boundaries. You should take great care to place the loudspeaker pair
to an exact symmetry in the listening room to maintain similar
frequency responses for both speakers. This also implies that the
listening room itself should be symmetrial along the axis between the
speakers to fulfill this requirement. This is usually true for modern
control room designs.
The second method is to push the speaker as close to the wall as
possible to decrease the time delay of this reflection relative to the
direct sound. This moves the interference problem to a higher
frequency, where the speaker's own directivity decreases the
rearward radiation and in this way the amplitude of the reflected
sound attenuates effectively relative to the direct sound. Then, you
should compensate the resulting boost of the bass frequencies by
using the room response controls.
AIM THE MONITORS TOWARDS THE LISTENER
The loudspeaker naturally becomes more directive as the frequency
increases, and the speaker has a certain acoustical axis where the
 response has been optimized. The response of the Genelec speakers
 has been specially optimized for a wide listening area. The monitors
should be directed towards the listener. The frequency response at
the listening position should be measured, and the room response
controls should be adjusted to obtain correct balance of the frequency
response, if needed. You can find this adjustment in the Genelec
speakers. Sometimes it is not possible to place the monitors to the
same height with the listeners ears, although this is desirable. If you
have to place the speakers high, you should aim them towards the
listener. This removes the effects of the increaseing directivity as the
frequency increases.
INTEGRATION TO IMAGES IN TV AND FILM MONITORING
The height of the speakers is particularly important when you are
to the width of your stereo base. For film mixing, it is customary to
setmixing a film or a TV programme. Then, you should also pay attention
the width of the stereo base to equal the width of the picture. For TV
work, however, you set the loudspeakers to approximately the
standard stereo base although the TV picture is much smaller. These
aspects seem to be a topic of continuous debate, and they should be,
because the decisions on the width of the stereo base significantly
affect the sound mix.
BATTLING THE ROOM MODES
An enclosed dynamic speaker behaves like a pressure source, and
placed near the wall will excite standing waves in room. The only
effective way to overcome this problem is to heavily damp the rear
wall of the control room at low frequencies with absorption material.
SUMMARY
High quality nearfield monitoring requires an exactly symmetrical
loudspeaker placement. The monitors should be carefully aimed
towards the listener, and the stereo base width and the height of the
monitors should be set according to the purpose of the mixing task.
End genelec.com text
This is the essense of what you need to set up a stereo system properly,
since most home stereo systems ARE free-standing. This is an excellent
guide!
Bonnie *:>
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