Beam Width Control; Beam Direction Control - Bang & Olufsen BeoLab 90 Technical Sound Manual

Selectable Sound Designs
10-band Parametric Equaliser

1.1.1 Beam Width Control

When a recording engineer makes a
recording in a well-designed studio, he
or she is sitting not only in a
carefully-designed acoustical space,
but a very special area within that
space. In many recording studios,
there is an area behind the mixing
console where there are no reflections
from the sidewalls arriving just after
the direct sound from the
loudspeakers. This is accomplished
either by putting acoustically
absorptive materials on the walls to
soak up the sound so it cannot reflect
(as shown in Figure 1.5), or to angle
the walls so that the reflections are
directed away from the listening
position (as shown in Figure 1.6).
Figure 1.5: One way to reduce the prob-
lem of side wall reflections is to absorb
them at the walls so that there is no re-
flection. This is a solution often used in
recording studios, however, it also re-
sults in an unnatural-sounding "dead"
room.
"Reflection-free Zone"
Figure 1.6: An alternative method to re-
duce the problem of side wall reflections
is to re-direct them away from the lis-
tening position, producing a "reflection-
free zone". This method is often used
in recording studios that are initially de-
signed with the help of an experienced
acoustical consultant.
This is di erent from your living room
which has not be designed primarily as
an acoustical space. It has sidewalls
that reflect the energy from your
loudspeakers and send that sound to
you at the listening position – a
situation that is more like that which is
shown in Figure 1.7.
"Reflection-free Zone"
Figure 1.7: The direct sound (in red)
from the loudspeakers is influenced by
the reflections o the side walls (in
grey).
In order to get the same acoustical
behaviour in your living room that the
recording engineer had, we have to
reduce the amount of energy that is
reflected o the side walls. If we do not
want to change the room, one way to
do this is to change the behaviour of
the loudspeaker by focusing the beam
of sound so that it stays directed at the
listening position, but it sends less
sound to the sides, towards the walls.
This is one of the options that BeoLab
90 gives you – to make the beam of
sound directed out the front of the
loudspeaker narrower to reduce the
level of sidewall reflections, so that you
8
"Reflection-free Zone"
get a more accurate representation of
the sound the recording engineer
heard when the recording was made.
Figure 1.8: BeoLab 90 solves the prob-
lem of side wall reflections by reduc-
ing the amount of acoustic energy that
is radiated towards the side walls – so
there is less energy to reflect.
However, if you're sharing your music
with friends or family, depending on
where people are sitting, the beam
may be too narrow to ensure that
everyone has the same experience. In
this case, it may be desirable to make
"Reflection-free Zone"
BeoLab 90's sound beam wider.
Of course, this can be extended to its
extreme where the BeoLab 90's beam
width is extended to radiate sound in
all directions equally. This may be a
good setting for cases where you have
many people moving around the
listening space, as may be the case at
a party, for example.
This option to change the pattern of
the radiation of sound from the BeoLab
90 is called Beam Width Control.

1.1.2 Beam Direction Control

Almost all loudspeakers are designed
to radiate sound forwards – so, in order
to get the best experience from your
loudspeakers, you have to be located
directly in front of them. However,
BeoLab 90 gives you the freedom to
change the direction of the sound
beam directed from the loudspeaker.
You can select one of five directions as
being the "acoustical front" of the
loudspeaker. If you're sitting to the
side of the loudspeaker as is shown in
Figure 1.2 you can choose to rotate the
sound beam so that it is directed more
towards your listening position instead
of in front of the loudspeakers.