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CHAPTER 4
Engaging the Lo-Cut lter
Using the LD-1A, LD-2 or LD-3 Lo-Cut lter (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 at frequency response with a minimal
area of overlap. The UPJ-1P loudspeakers in the system
receive their signal following a high-pass lter, while the
subwoofers apply their normal internal crossover frequen-
cies to a full range signal. To achieve this at response, the
subwoofers need to have their polarity reversed.
TIP: The atness of the response is, in any
case, dependent on proximity to boundary
surfaces.
While the change of polarity with respect to a daisy-chained
conguration is needed due to the phase shift caused by
the high-pass lter 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 lter engaged,
and 650-P or USW-1P subwoofers in their full-range
conguration — 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 lters in use in
the DSP is using increases.
In no case should a lter 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/lter 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 2nd (-12dB/oct) 162 Hz 0.82*
*If the DSP does not have variable Q for high-pass lters, the lter 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.