A White Paper Of The Installation Series Loudspeakers
2) Discussion on phase response when
multiple speaker systems are used
For installation to a hall, theater, church, etc.,
multiple speakers may be stacked in arrays.
In such conditions, there may be a problem in
the overlapped area where more than one
speaker covers. That is, as described in 2-1)
above, there may be a dip in the amplitude
response.
This is because of the phase difference that is
caused by the distance difference between the
speaker position and the listening position.
Therefore, from the view point of the system
design, it is very important to reduce the
overlapped area but actually it is very difficult
to perfectly eliminate it. Under the condition
where two speakers are used as shown in
Figure 6, Table 1 shows the relation between
the "distance difference" and "out-of-phase
frequency". The distance difference shows the
difference between the distances from these
speakers to the testing point. The frequency
shows the point where the phase difference
caused by the distance difference is 90 degrees.
The parameter θ is the angle with the center
axis.
Table 1 indicates the following.
When the overlapped area is within 10 degrees,
the phase difference caused by the distance
difference in the overlapped area is within 90
degrees at 1 kHz or less frequency, regardless
of the distance from the sound source.
When the overlapped area is within 20 degrees,
the phase difference is within 120 degrees at 1
kHz or less frequency. It is thought that, under
this amount of phase difference, interference
can be ignored. Therefore, in this condition, it
is very important to match the phase
characteristics of two speakers in order to get
the amplitude characteristics with no dip (as
with the discussion of phase characteristics
between drivers described earlier).
(Note that, practically, because the directivity
of a speaker changes depending on frequency,
you have to consider frequency, directivity and
distance.)
<Figure 6: Considering the characteristics in the
overlapped area>
<Table 1: The relation between the distance difference and
out-of-phase frequency in the overlapped area>
θ L=6 m L=12 m L=24 m
5 0,174 /
3 3252 Hz
0,174 /
3.249 Hz
0,174 /
3.248 Hz
10 0,347 /
1.627 Hz
0,347 /
1.626 Hz
0,347 /
1.626 Hz
15 0,517 /
1.087 Hz
0,517 /
1.086 Hz
0,518 /
1.085 Hz
20 0,683 /
817 Hz
0,684 /
816 Hz
0,684 /
816 Hz
Phase difference = 90 degrees
2ft
θ
L
dl
Overlap Area
- 5 -
(17 pages)
(11 pages)
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Comments to this Manuals