Bang & Olufsen BeoLab 90, Техническое руководство по звуку

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Frequency [Hz]
Horizontal Angle [°]
Beam Width: Omni
100 1000 10,000
− 150
− 100
− 50
0
50
100
150
− 12
− 10
− 8
− 6
− 4
− 2
0
Figure 5.18: Full frequency range direc-
tivity plot of the Omni Beam. Latency:
Long. Contours in steps of 3 dB, nor-
malised to the on-axis response.
The side effects of the Omni beam
width are similar to those of the Wide
beam width – the only difference is
that they are more noticeable.
Distances to sound sources become
even more similar to the distance the
loudspeakers, left-right imaging
becomes less precise (but more
forgiving of incorrect listener
placement), and the influence of wall
reflections becomes more audible.
tri
tri
tom
tom
tom
hh
voice
bongos
bk
bk
bass
bass
gtr
synth pad at end
sax
snare
"choir"
"choir"
cow
synth fx around 2:20
shake
tri
tri
Figure 5.19: A map of the phantom im-
age location of the voice (shown in red)
in Suzanne Vega’s recording of Tom’s
Diner. Beam Width: Omni. Compare to
Figure
5.3
tri
tri
tom
tom
tom
hh
voice
bongos
bk
bk
bass
bass
gtr
synth pad at end
sax
snare
"choir"
"choir"
cow
synth fx around 2:20
shake
tri
tri
Figure 5.20: A map of the phantom im-
age locations of instruments and voices
in Jennifer Warnes’s recording of Bird on
a Wire. Beam Width: Omni. Compare to
Figure
5.4
In addition, in cases where the
loudspeakers are located near a rear
wall, the timbral effects of reflections
from behind the loudspeakers may also
become more audible.
Experienced readers will notice that,
although in the low frequency bands,
the “omni” setting results in an
omnidirectional directivity, there are
measurable “lobing” effects in the
higher frequency bands. This is
primarily caused by the distances
between the midrange and tweeters
which have been optimised for the
narrow beam width, however, in a
passive listening or background music
situation, this will not detract from the
overall performance of the
loudspeaker.
5.1.4 Comment
Note that the above illustrations
connecting Beam Widths to listener
position are merely that – illustrations.
It should also be said that changing the
Beam Width of the BeoLab 90 has
non-intuitive consequences on the
perceived sound of the loudspeakers.
For example, the overall sensation of
“punch” in the bass may be different
for the three Beam Widths, regardless
of your location in the listening room.
Consequently, it may be that you
prefer the overall sound of a particular
Beam Width, even if you are not sitting
“in the beam”.
5.2 Beam Direction Control
There may be cases where you are
sitting off-axis to the loudspeakers, far
away from the so-called “sweet spot”
in the listening room. Depending on
the placement of your loudspeakers,
this may even include listening
positions that are behind the
loudspeakers. In these situations, it
may be desirable to change the
principal direction of radiation of the
sound from the BeoLab 90’s, rotating
the beam so that it is better directed
towards the listening position. This is
possible using the Beam Direction
Control feature of the BeoLab 90.
When the Beam Width is set to “Wide”,
it is possible to change the direction of
the beam by selecting from five
options:
• Front
• Front Left
• Front Right
• Back Left
• Back Right
These five directions are illustrated in
Figure 1.9 as well as Figures 5.9 , 5.22 ,
and 5.23 .
It should be noted that the Beam
Direction control is only available when
the Beam Width control is set to
“Wide”. This is because the narrow
beam width is only possible due to the
cluster of three tweeters and three
midrange drivers on the front of the
loudspeaker. Also, since the omni
beam width is circular, its rotation
would be redundant.
Figure 5.21: Press the curved line shown
above to change the Beam Width to
Wide with a Left Front direction.
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