Chapter 2: Amplification And Audio; Audio Input - Meyer Sound MILO Operating Instructions Manual

CHAPTER 2: AMPLIFICATION AND AUDIO

More than just a self-powered loudspeaker, MILO 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's
amplifier and audio systems.

AUDIO INPUT

The MILO loudspeaker presents a 10 kOhm balanced input
impedance to a three-pin XLR connector with the following
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 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 reversed.
Any number of MILO loudspeakers – even one – in
the array with reversed polarity will result in severe
degradation in frequency response and coverage.
TIP: If abnormal noises such as hiss and
popping are produced by the loudspeaker,
disconnect the audio cable from the loudspeaker.
If the noise stops, then 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 loudspeaker
(Figure 2.1). A single source can drive multiple MILO
loudspeakers with a paralleled input loop, creating an
unbuffered hard-wired loop connection.
Figure 2.1: MILO's rear panel audio input connectors
When driving multiple MILO 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 loudspeaker is 10 kOhms: if n represents
the number of MILO loudspeakers in an array, paralleling
the inputs of n MILO loudspeakers 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 loudspeakers produces an input impedance 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 loudspeakers in parallel (loop
out) with other self-powered Meyer Sound loudspeakers, for
example M3D's, M3D-Subs, M2Ds, or 650-Ps.
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