Meyer Sound M1D - Manual (Page 20)

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CHAPTER 4
NOTE: When driving M1D loudspeakers
from the Mid-Hi output of the LD-1A, LD-2 or
LD-3 line driver with the Lo-Cut filter engaged and
M1D-Sub loudspeakers in their Sub-out full-range
configuration, their polarities should be kept the op-
posite if they are co-planar or near each other.
This can be achieved by engaging the polarity
reverse switch on the subwoofer output of the line
driver. If your M1D and M1D-Sub loudspeakers are
separated – or delay must be used between them
– a measurement system such as the SIM audio
analyzer should be used to determine the correct
delay and polarity.
TIP: How flat the response will be 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
M1D-Sub loudspeakers more than 4 feet apart from M1D
loudspeakers may require reversing the polarities once
again to compensate for the delay propagation.
LD-3 OPTIONS
In addition to the 160 Hz high-pass filter on the LD-3 com-
pensating line driver, the LD-3 provides additional filter-
ing capabilities (Table 4.1) to help you further fine-tune an
M1D/M1D-Sub system.
Table 4.1 M1D and M1D-Sub Frequency Response Results with Dif-
ferent Filter Configurations
HPF LPF ø Reverse
Switch Result
Off Off Off Flat response (Small rise in the 80 to
150 Hz range)
80 80 Engaged Flat response, +3 dB sub gain rec-
ommended
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 due to phase shifts that can cause cancellations.
If DSP is used, both M1D and M1D-Sub loudspeakers
should be fed from the DSP in order to keep their delay
time the same. Otherwise you may experience phase shift
differences between the M1D and M1D-Sub loudspeakers.
In addition, you should verify the delay time between chan-
nels: 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 the DSP is us-
ing 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 are set to emulate the low-cut LD-1A/LD-2
and LD-3 (160 Hz position) characteristics themselves, as
shown in Table 4.2.
Table 4.2: LD-1, LD-2 and LD-3 (LD-3 at 160 Hz) “Lo-Cut Filter”
Parameters
Type Order Pole
Frequency Q
High Pass 2nd
(-12dB/oct) 162Hz 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 audio analyzer and the
CP-10 parametric equalizer are both highly recom-
mended.