Meyer Sound M3D - Manual (Page 13)

Meyer Sound Laboratories Inc M3D™ Line Array • 7
M3D-Sub Interconnections
Each front 4 ohm, 18-inch, low-frequency driver is
powered by one channel of the HP-4/M3D-Sub amplifier;
also, each rear 8 ohm, 15-inch low-frequency driver is
powered by one amplifier channel. Figure 13 shows how
the drivers are connected to the amplifier in the
M3D-Sub.
T HE T RU P OWER ™ L IMITING S YSTEM
Conventional limiters assume that the impedance of a
speaker remains constant and set the limiting threshold
by measuring voltage only. This method is inaccurate,
because the speaker’s impedance changes in response to
the frequency content of the source material and thermal
variations in the speaker’s voice coil and magnet.
Conventional limiters begin limiting prematurely, which
under utilizes system headroom and deprives the
speaker of its full dynamic range.
The TruPower Limiting (TPL) system accounts for varying
speaker impedance by measuring current, in addition to
voltage, to compute the actual power dissipation in the
voice coil. TPL improves performance before and during
limiting by allowing each driver to produce its maximum
SPL across its entire frequency range. TPL extends the
lifetime of the drivers by controlling the temperature of
the voice coil. In addition, TPL eliminates power
compression when the system is operated at high levels
for extended periods.
The true power is monitored for each of the four
amplifier channels. When the safe continuous power level
is exceeded, the TPL limiter controlling that amplifier
channel engages. TPL activity is indicated by the LEDs on
the user panel.
The M3D and M3D Sub perform within their acoustical
specifications and operate at a normal temperature if the
limit LEDs are lit for no longer than two seconds, and off
for at least one second. If either LED remains on for
longer than three seconds, that channel is hard limiting
with the following negative consequences:
■ Increasing the input level will not increase the
volume.
■ The system distorts due to clipping and nonlinear
driver operation.
■ The lifespan of the drivers is reduced because they
are subjected to excessive heat.
M3D TPL Limiters
The left-and-right front low-frequency drivers are
driven by separate amplifier channels but are routed to
one limiter; the LO TPL F LED on the user panel indicates
TPL activity for the front drivers. The two rear low-
frequency drivers are driven by one amplifier channel;
the LO TPL R LED indicates TPL activity for the rear low-
frequency drivers. The two high-frequency drivers are
driven by one amplifier channel; the HI Limit LED, shown
in Figure 14 on page 7, indicates TPL activity for the
high-frequency drivers.
The limiters cease operation when the power level in the
channel returns to normal and do not affect the signal
when the LED is inactive.
Figure 13. M3D-Sub internal wiring harness diagram
Red Black Red Black
Right Front MS-418 N Left Front MS-418 N
Right Rear MS-815 Left Rear MS-815
-
+
+
-
-
+
+
-
Red Black Red Black
-
+
-
+
Fans
User Panel
M3D-Sub
HP Amplifier Chassis
(Top View)
Upper Control Card (Front)
24.033.042.32
Lower Control Card (Rear)
24.033.042.31
Figure 14. M3D Limit LEDs