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CHAPTER 3: AMPLIFICATION AND AUDIO
Pins 2 and 3 carry the input as a differential signal. Pin 1 is
connected to earth through a 1 kOhm, 1000 pF, 15 V
clamped network. This circuitry provides virtual ground lift
for audio frequencies while allowing unwanted signals to
bleed to ground. Make sure to use balanced XLR audio
cables with pins 1–3 connected on both ends. Telescopic
grounding is not recommended and shorting an input
connector pin to the case may cause a ground loop,
resulting in hum.
TIP:
If unwanted noise or hiss is produced by the
loudspeaker, disconnect its input cable. If the
noise stops, there is most likely nothing wrong with the
loudspeaker. To locate the source of the noise, check
the audio cable, source audio, AC power, and electri-
cal ground.
Audio Loop Output (XLR 3-Pin or 5-Pin Male)
The XLR 3-pin or 5-pin male Loop output connector allows
multiple loudspeakers to be looped from a single audio
source. The Loop output connector uses the same wiring
scheme as the Input connector (see "Audio Input (XLR 3-Pin
or 5-Pin Female)" on page 17). For applications that require
multiple 1100-LFCs, connect the Loop output of the first
loudspeaker to the Input of the second loudspeaker, and so
forth.
NOTE:
The Loop output connector is wired in
parallel to the Input connector and transmits
the unbuffered source signal even when the loud-
speaker is powered off.
Calculating Load Impedance for Looped Audio
Signals
To avoid distortion when looping multiple loudspeakers,
make sure the source device can drive the total load
impedance of the looped loudspeakers. In addition, the
source device must be capable of delivering approximately
20 dBV (10 V rms into 600 ohms) to yield the maximum SPL
over the operating bandwidth of the loudspeakers.
To calculate the load impedance for the looped
loudspeakers, divide 10 kOhms (the input impedance for a
single loudspeaker) by the number of looped loudspeakers.
For example, the load impedance for ten 1100-LFCs is
1000 ohms (10 kOhms / 10). To drive this number of looped
loudspeakers, the source device should have an output
impedance of 100 ohms or less. This same rule applies when
looping 1100-LFCs with other Meyer Sound self-powered
loudspeakers.
18
NOTE:
Most source devices are capable of
driving loads no less than 10 times their output
impedance.
TIP:
Audio outputs from Meyer Sound's
Galileo GALAXY Network Platform have an out-
put impedance of 50 ohms. Each output can drive up
to 20 Meyer Sound (10 kOhm) loudspeakers without
distortion.
CAUTION:
Make sure that all cabling for
looped loudspeakers is wired correctly (Pin 1
to Pin 1, Pin 2 to Pin 2, and so forth) to prevent the
polarity from being reversed. If one or more loud-
speakers in a system have reversed polarity, fre-
quency response and coverage will be significantly
degraded.
CABLE RINGS
Two cable rings are provided on the rear of the 1100-LFC
cabinet (Figure 12). Power and audio cables should be tied
off to the rings to reduce strain on the cables and prevent
damage to them during installation. The cable rings should
not be used for any other purpose.
Figure 12: Cables Tied Off to Cable Ring
CAUTION:
The 1100-LFC cable rings should
only be used to reduce strain on cables. The
cable rings should not be used for any other purpose.
TRUPOWER LIMITING
The 1100-LFC employs Meyer Sound's advanced
®
TruPower
limiting. Conventional limiters assume a constant
driver impedance and set the limiting threshold by
measuring voltage alone. This method is inaccurate
because driver impedances change as frequency content in
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