17
CHAPTER 5
Using the LD-3’s filters helps to easily integrate and op-
timize your M Series array with 700-HP subwoofers. The
use of high-pass filters (HPF) augment array headroom by
removing lower frequencies near the array loudspeaker’s
lower operating range, while low-pass filters (LPF) can
remove unwanted mid-low frequencies reproduced by the
array or stack of subwoofers. The use of these filters re-
duces the area of overlap and minimizes the interaction and
possible cancellations between subsystems, usually result-
ing in highly desirable behavior, such as very flat frequency
response.
As shown in Tables 5.1 through 5.3, the LD-3’s filtering
capabilities can go a long way toward fine-tuning your
system, when using the 700-HP subwoofer with M Series
loudspeakers. All data in these tables are based on designs
in a close-proximity, coplanar orientation, at a 2:1 ratio of
loudspeakers to subwoofers. Out of all possible combina-
tions, these yield the flattest frequency response.
Table 5.1. MILO Models and 700-HP
HPF
LPF
ø Reverse Switch
Result
Off
Off
Engaged
Boost in the 100 Hz
region
160
Off
Engaged
Very flat response
80
80
Off
Very flat response
160
80
Off
Flat response
Table 5.2. M3D and 700-HP
HPF
LPF
ø Reverse Switch
Result
Off
Off
Engaged
Flat response
Off
55
Engaged
Flat response
80
55
Off
Very flat response,
+6 dB sub gain
recommended
160
80
Off
Very flat response,
+6 dB sub gain
recommended
Table 5.3. M2D and 700-HP
HPF
LPF
ø Reverse Switch
Result
Off
55
Off
Flat response,
-6 dB sub gain
recommended*
80
80
Engaged
Very flat response,
-6 dB sub gain
recommended*
* Unlike the matched sensitivity of the M2D and M2D-Sub, the 700-HP is +6 dB more sensitive
than the M2D/M2D-Sub.
NOTE:
The use of external filters — like the
ones in the LD-3 — should be used very
carefully to minimize phase shifts that can cause
cancellations.
NOTE:
When driving the system using the
LD-3 with the filters engaged, a change of
polarity on the Sub Output might be needed due to
the phase shift caused by the filters at overlapping
frequencies. Placing the subwoofers more than 4
feet apart may require reversing the polarities once
again to compensate for the delay propagation. If
they are separated by a greater distance — or delay
must be used between them — a measurement sys-
tem such as the SIM audio analyzer should be used
to determine the correct delay and polarity.
700-HP USED IN COMBINATION WITH THE
650-P SUBWOOFER
With its different low-frequency drivers, amplification and
cabinet tuning, output capabilities and extended low-end
headroom, the 700-HP is not the same subwoofer as Meyer
Sound’s 650-P. However, the phase response of both mod-
els is identical, making it possible to deploy 700-HP/650-P
combinations.
For this situation, three 650-P subwoofers should be used
for every two 700-HP subwoofers to avoid over-working
the 650-Ps while fully utilizing the 700-HP’s output power.
Although both models will, in general, limit in approximately
the same way, their exact limiting behavior will vary with the
frequency content of the signal fed to the subwoofers.
NOTE:
There is no polarity switch on the
700-HP and it is wired pin 2 “hot” (positive
acoustic pressure when a positive pulse is applied
to pin 2). When 700-HP subwoofers are used with
650-P subwoofers, their polarities must be kept the
same (set the switch on the rear of the 650-P to
Pin 2+).
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 Meyer Sound loudspeakers and 700-
HP subwoofers should be fed from the DSP in order to keep
their delay time the same. Otherwise, you may experience
phase shift differences between the loudspeakers and the
subwoofers. 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 the DSP is using increases.
