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CHAPTER 3: AMPLIFICATION AND AUDIO
More than just a self-powered loudspeaker, MILO 120 uses
sophisticated amplification and protection circuitry and
an advanced limiting system to produce consistent and
predictable results in any system design. This chapter will
help you understand and harness the power of MILO 120's
amplifier and audio systems.
AUDIO INPUT
The MILO 120 loudspeaker presents a 10 kOhm balanced
input impedance to a three-pin XLR connector with the fol-
lowing connectors:
■ Pin 1 — 220 kOhm to chassis and earth ground (ESD
and RF clamped)
■ Pin 2 — Signal ( + )
■ Pin 3 — Signal ( - )
■ Case — Earth (AC) ground and chassis
CAUTION:
Shorting an input connector pin
to the case can form a ground loop and
cause hum.
Pins 2 and 3 carry the input as a differential signal; pin 2 is
hot relative to pin 3, resulting in a positive pressure wave
when a positive signal is applied to pin 2. Pin 1 is connected
to earth through a 220 kOhm, 1000 pF, 15 V clamp network.
This ingenious circuit provides virtual ground lift at audio
frequencies, while allowing unwanted signals to bleed to
ground. Use standard audio cables with XLR connectors
for balanced signal sources. Make sure that pin 1 (shield) is
always connected on both ends of the cable. Telescoping
grounding schemes are not recommended.
CAUTION:
Ensure that all cabling carrying
signal to MILO/ MILO 120 loudspeakers in an
array is wired correctly: Pin 1 to Pin 1, Pin 2 to Pin 2,
and so forth, to prevent the polarity from being re-
versed. Any number of MILO/MILO 120 loudspeak-
ers (even one) in the array with reversed polarity will
result in severe degradation in frequency response
and coverage.
TIP:
If abnormal noises such as hissing and
popping are produced by the loudspeaker,
disconnect the audio cable from the loudspeaker. If
the noise stops, most likely the problem is not with
the loudspeaker. Check the audio cable, source and
AC power to pinpoint the problem.
Audio signals can be daisy-chained using the loop output
connector on the user panel of the MILO 120 loudspeaker
(Figure 3.1). A single source can drive multiple MILO/MILO
120 loudspeakers with a paralleled input loop, creating an
unbuffered hard-wired loop connection.
Figure 3.1.
MILO 120's rear panel audio input connectors
When driving multiple MILO/MILO 120 loudspeakers in an
array, make certain that the source device can drive the
total load impedance presented by the paralleled input
circuit of the array. The source device must be capable of
producing a minimum of 20 dB volts (10 volts rms into 600
ohms) in order to produce the maximum peak SPL over the
operating bandwidth of the loudspeaker.
To avoid distortion, make sure the source device provides
an adequate drive circuit design for the total paralleled load
impedance presented by the array. The input impedance
for a single MILO/MILO 120 loudspeaker is 10 kOhms: if n
represents the number of MILO/MILO 120 loudspeakers in
an array, paralleling the inputs of n MILO/MILO 120 loud-
speakers will produce a balanced input load of 10 kOhms
divided by n.
NOTE:
Most source devices are safe for
driving loads no smaller than 10 times the
source's output impedance.
For example, cascading an array of 10 units consisting of
MILO/MILO 120 loudspeakers produces an input imped-
ance of 1000 ohms (10 kOhms divided by 10). The source
device should have an output impedance of 100 ohms or
less. This is also true when connecting MILO/MILO 120
loudspeakers in parallel (loop out) with other self-powered
Meyer Sound loudspeakers, for example M3D, M3D-Sub,
700-HP, or 650-P models.
CHAPTER 3
11
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