Daisy-Chained; Adding A Line Driver; Engaging The Lo-Cut Filter - Meyer Sound M SERIES Operating Instructions Manual

CHAPTER 4
In addition, the use of high-pass filters to drive an M2D
system with the M2D-Sub flattens overall frequency
response and slightly increases M2D headroom in the
lowest end of its usable spectrum.
The ideal ratio of M2D to M2D-Sub loudspeakers depends
on the configuration of the system, the application, and the
frequency content of the signal being reproduced. For most
applications, two M2Ds for each M2D-Sub yields good
results in frequency response and headroom.
NOTE: The M2D-Sub limit LEDs indicate
when its safe power level is exceeded. If
the M2D-Sub loudspeakers used in a system begin
to limit before reaching the required SPL at low
frequencies, you may need to add more M2D-Subs
to satisfy the SPL requirements without exposing
the drivers to excessive heat and/or excursion.
The M2D and M2D-Sub loudspeakers can accommodate
three basic connection options.

Daisy-Chained

When M2Ds and M2D-Subs are daisy-chained using the
loop feature on the user panel, the result will have a fairly
flat frequency response. However, at a ratio of two M2D to
each M2D-Sub loudspeaker, the response will have a rise in
the 70 to 160 Hz range where the frequency of the M2D and
M2D-Sub overlap.
CAUTION:
Always ensure that the source
equipment can drive the total load of the
paralleled system.
NOTE: When both and M2D and M2D-Sub
loudspeakers are used in their full-range
configuration (e.g., looped audio or the same audio
feed), their polarities should be kept the same if
they are co-planar or near each other. If they are
separated by a greater distance – 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.

Adding a Line Driver

Driving an M2D/M2D-Sub system with the same signal from
different outputs using a line driver allows adjustments to
the gain and polarity of each sub-system, and could be used
effectively to compensate for the ratio of loudspeakers or
20
acoustical conditions. If the gains are adjusted to the same
level, the combined response is identical to a daisy-chain
configuration with a rise in level on the overlapping range.
Meyer Sound makes available three different line drivers.

Engaging the Lo-Cut Filter

Using the LD-1A, LD-2 or LD-3 Lo-Cut filter (the 160 Hz
HPF position on the LD-3) can produce an M2D/M2D-
Sub system (in close proximity and co-planar) with very
flat frequency response and a minimal area of overlap.
The M2D loudspeakers in the system receive their signal
following a high-pass filter, while the M2D-Subs apply their
normal internal crossover frequencies to a full range signal.
NOTE:
When driving M2Ds from the Mid-
Hi output of the LD-1A, LD-2 or LD-3 line
driver with the Lo-Cut filter engaged and M2D-Sub
loudspeakers in their full-range configuration, their
polarities should be kept the opposite 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 M2D and
M2D-Sub loudspeakers are separated by a greater
distance – 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
M2D-Sub loudspeakers more than 4 feet apart from M2D
loudspeakers may require reversing the polarities once
again to compensate for the delay propagation.
Table 4.1: M2D and M2D-Sub frequency response results with LD-
1A, LD-2 and LD-3 (160 Hz filter)
Lo-Cut ø Reverse Result
Switch
Off Off Flat response (small rise on 70 Hz -160
Hz area)
Engaged Engaged Very flat response