L-Acoustics V-DOSC, Руководство оператора

Страница: 143 / 158

L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 143 of 158
For example when
δ
d = 0.33 m (i.e.
δ
t = 1 msec), cancellations occur at 500 Hz, 1500 Hz,
2500 Hz, ... producing what is termed comb filtering. The biggest problem with comb filtering is
the fact that these cancellations are not consistent with frequency since the time difference
changes depending on the observer location M.
Figure 102: Comb filtering due to path length differences between sources
As discussed in Section 3.3, the principles of 2 source interference can be used in sound design
when considering multiple V-DOSC arrays since, in effect, the main and offstage V-DOSC arrays
act as 2 coherent sound sources. When a separation of 6-8 metres is maintained between the 2
V-DOSC arrays, this shifts the first octave-wide cancellation seen in Figure 102 (f
o
) down to
approximately 15-25 Hz and this cancellation becomes inaudible since it is shifted below the
operating bandwidth of the V-DOSC low section. The second and third nulls (3f
o
, 5f
o
) tend to be
filled in or masked by room reverberation. Higher frequency cancellations (7f
o
and higher) are
too tightly spaced for the ear to resolve, plus focussing the aiming axes of the two arrays at
different angles helps to minimize the area over which this comb filtering interaction takes place.