Meyer Sound Compact VariO UPJ-1P, Operating Instructions Manual

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CHAPTER 4
Engaging the Lo-Cut filter
Using the LD-1A, LD-2 or LD-3 Lo-Cut filter (160 Hz posi-
tion on the LD-3) with a system comprising UPJ-1P loud-
speaker and subwoofers in close proximity and co-planar
will produce a very flat frequency response with a minimal
area of overlap. The UPJ-1P loudspeakers in the system
receive their signal following a high-pass filter, while the
subwoofers apply their normal internal crossover frequen-
cies to a full range signal. To achieve this flat response, the
subwoofers need to have their polarity reversed.
TIP:
The flatness of the response is, in any
case, dependent on proximity to boundary
surfaces.
While the change of polarity with respect to a daisy-chained
configuration is needed due to the phase shift caused by
the high-pass filter at overlapping frequencies, placing sub-
woofers more than 4 feet apart from UPJ-1P loudspeakers
may require reversing the polarities once again to compen-
sate for the delay propagation.
NOTE: When driving UPJ-1P loudspeak-
ers from the Mid-Hi output of the LD-1A or
LD-2 line driver — with the Lo-Cut filter engaged,
and 650-P or USW-1P subwoofers in their full-range
configuration — their polarities should be reversed if
they are co-planar or near each other. The simplest
way to achieve this is engaging the “reverse polar-
ity" switch in the sub output of the line driver.
If your UPJ-1P loudspeakers and 650-P or USW-1P
subwoofers are separated by a greater distance - or
delay must be used between them - a measurement
system such as SIM should be used to determine
the correct delay and polarity.
DIGITAL SIGNAL PROCESSORS
Full-range signals may be applied to Meyer Sound’s self-
powered loudspeakers because they have built-in active
crossover circuits; external crossovers and digital signal
processors (DSP) are optional and should be used very
carefully as phase shifts can cause destructive cancella-
tions.
If DSP is used, both UPJ-1P loudspeakers and subwoofers
should be fed from the DSP in order to keep their delay time
the same. Otherwise you may experience phase shift differ-
ences between the UPJ-1P loudspeakers and the subwoof-
ers. In addition, you should verify the delay time between
channels: Some DSPs may develop channel-to-channel
delay errors when the DSP is near maximum throughput,
which becomes more likely as the number of filters in use in
the DSP is using increases.
In no case should a filter higher than 2nd order be used.
The additional phase shift introduced deteriorates the im-
pulse response and higher roll-off does not improve cross-
over interaction. In fact, it is highly recommended that the
crossover/filter is set to emulate the low-cut LD-1A/LD-2
and LD-3 (160 Hz position) characteristics themselves, as
shown in Table 4.1.
Table 4.1: LD-1/LD-2/LD-3 Lo-Cut Filter Parameters
Type Order Pole Frequency Q
High Pass 2
nd
(-12dB/oct) 162 Hz 0.82*
*If the DSP does not have variable Q for high-pass filters, the filter should be
set to “Butterworth” (Q
≈
.7).
If the loudspeakers are going to be driven directly from DSP,
verify that the outputs of the processor have the driving ca-
pabilities to drive the total load presented by the loudspeak-
ers connected to it.
NOTE:
When precise array design, subwoof-
er integration, DSP and delay systems, and
compensation for acoustical conditions all come
into play, measurement and correction tools are a
must. Meyer Sound’s SIM measurement system
and the CP-10 parametric equalizer are both highly
recommended.