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ChAPTER 2: ThE mm-4CEU CONTROL ELECTRONICS UNIT
The MM-4CEU is a required component for every MM-4
installation. It performs a number of important signal-
processing functions to ensure that the MM-4 meets its
published specifications and is protected against damaging
overload conditions.
The MM-4CEU mounts in a standard 19-inch relay rack and
occupies a single rack space (1.75 inches). Each MM-4CEU
provides two channels of signal processing, both capable
of driving several amplifier channels and monitoring two
separate amplifier channels for protection (four amplifier
channels total per MM-4CEU). Each channel of the
MM-4CEU features an independent signal level attenuator
and low cut switch.
NOTE:
See Chapter 3, "Choosing a Power
Amplifier," for important details about
choosing and configuring an amplifier for use with
the MM-4CEU.
fREqUENCy AND PhASE RESPONSE
CORRECTION
The MM-4CEU incorporates multiple-pole frequency
response equalization circuitry that is tailored specifically
to the MM-4 loudspeaker's acoustical characteristics. This
circuitry assures that the MM-4's response remains within
±4 dB from 160 Hz to 16 kHz (free field). Integral phase
response correction circuits maintain a system phase
response of ±45° from 700 Hz to 17 kHz.
The MM-4CEU also provides an independent front-
panel low-cut switch for each signal channel. This switch
introduces a high-pass function that can be used to
compensate for low-frequency boost due to half-space
loading in flush-mounted configurations. It can also
augment the MM-4 loudspeaker's headroom when used
with a subwoofer for music reproduction.
NOTE:
See the section "Equalization" in
Chapter 3, "Choosing a Power Amplifier," for
more information on using the low-cut switch on the
MM-4CEU.
DRIVER PROTECTION
The MM-4CEU features Meyer Sound's SpeakerSense
driver protection circuitry. Through a connection back from
the power amplifier output, the MM-4CEU's SpeakerSense
function monitors the continuous and peak power being
applied to the MM-4 drivers. Meyer Sound's MultiSense
function then allows each MM-4CEU channel to monitor
two amplifier outputs, assuring that the protection circuits
are activated by the signal branch with the highest gain.
This allows the MM-4CEU to protect the MM-4 in the
following ways:
When the continuous power exceeds the MM-4's safe
limits, the MM-4CEU introduces an RMS limiter that
clamps the audio signal to protect the MM-4 driver from
damage due to overheating.
When the peak power exceeds the MM-4's safe limits,
the MM-4CEU introduces a fast-acting peak limiter to
clamp the signal level and protect the MM-4 driver from
excessive excursion.
The functions of the SpeakerSense circuitry are indicated
on the MM-4CEU front panel by the following LEDs on each
channel:
Peak Limit — During peak limiting, the Peak Limit LED
glows yellow.
RMS Limit — During RMS limiting, the RMS Limit LED
glows yellow.
Sense — When sensing, the MM-4CEU may display
one of two LED colors:
-
When the signal is sensed back through the
SpeakerSense connection, the LED glows green.
-
When the gain of the amplifier is below 10 dB or
above 30 dB, the LED flashes red, indicating that
the protection will not work properly.
When a channel returns to normal, limiting ceases. The
LED for that channel is inactive, indicating MM-4CEU is not
currently limiting.
CHAPTER 2
5
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