Meyer Sound M1D - Manual (Page 13)

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CHAPTER 2
More than just self-powered loudspeakers, the M1D and
M1D-Sub use sophisticated amplification and protection
circuitry to produce consistent and predictable results in
any system design. This chapter will help you understand
and harness the power of the M1D and M1D-Sub amplifi-
cation and audio systems.
The rear panels of the M1D and M1D-Sub loudspeak-
ers (Figure 2.1) provide two slots for processor modules.
The upper slot contains the Audio Input, while the RMS™
module is located in the lower slot.
Figure 2.1. The rear panel of the M1D and M1D-Sub
AUDIO INPUT
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 con-
nected to earth through 220 kOhm, 1000 pF, 15 V clamp
network. This ingenious circuit provides virtual ground lift
for audio frequencies, while allowing unwanted signals to
bleed to ground. Use standard audio cables with XLR con-
nectors 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 M1D and M1D-Sub loudspeak-
ers 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 loudspeakers
— even one in the array — with reversed polar-
ity will result in severe degradation in frequency
response and coverage.
Audio signals can be daisy-chained using the loop output
connector on the user panel (Figure 2.1). A single source
can drive multiple M1D and M1D-Sub loudspeakers with
a paralleled input loop, creating an unbuffered hard-wired
loop connection.
When driving multiple M1D and/or M1D-Sub 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 audio source 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 from the source, make sure the source
equipment provides an adequate drive circuit design for
the total paralleled load impedance presented by the ar-
ray. The input impedance for a single loudspeaker is 10
kOhms: if n represents the number of M1D and M1D-Sub
loudspeakers in an array, paralleling the inputs of n loud-
speakers will produce a balanced input load of 10 kOhms
divided by n.
NOTE: Most source equipment is safe for
driving loads no smaller than 10 times the
source’s output impedance.
For example, cascading an array of 10 units consisting of
M1D and/or M1D-Sub loudspeakers produces an input
impedance of 1000 ohms (10 kOhms divided by 10). The
source equipment should have an output impedance of
100 ohms or less. This is also true when connecting M1D
and M1D-Sub loudspeakers in parallel (loop out) with
other self-powered Meyer Sound loudspeakers.
! CAUTION: Shorting an input connector pin
to the case can form a ground loop and
cause hum.
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 for the source of the prob-
lem.
CHAPTER 2: AMPLIFICATION AND AUDIO