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15
CHAPTER 3: AMPLIFICATION AND AUDIO
The Acheron drivers are powered by a two-channel propri-
etary Meyer Sound amplifier with MOSFET output stages. The
audio signal is processed with an electronic crossover, cor-
rection filters for phase and frequency response, and driver
protection circuitry. Each channel has peak and rms limiters
that prevent driver over-excursion and regulate the tempera-
ture of the voice coil.
The Acheron rear panel has an audio Input and Loop output
connector, Limit LEDs, and an optional RMS module for
connecting to the RMS remote monitoring system (see
Chapter 6, “The RMS Remote Monitoring System”).
AUDIO CONNECTORS
The Acheron and Acheron LF include female XLR Input and
male XLR Loop output connectors.
Input Connector
The female XLR Input connector accepts a balanced audio
signal with an input impedance of 10 kOhm. The connector
uses the following wiring:
■ Pin 1 — 220 kOhm to chassis and earth ground (ESD
clamped)
■ Pin 2 — Signal (+)
■ Pin 3 — Signal (–)
■ Case — Earth (AC) ground and chassis
Pins 2 and 3 carry the input as a differential signal. Pin 1 is
connected to earth through a 220 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 standard, balanced XLR
audio cables with all three pins 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, and AC
power.
Loop Output Connector
The male XLR Loop output connector allows Acheron and
Acheron LF loudspeakers to be looped from a single audio
source. For applications that require multiple Acherons and
Acheron LFs, connect the Loop output of the first unit to the
Input of the second, and so forth.
NOTE: The order in which loudspeakers are
connected when looping audio signals is unim-
portant. The Loop connector is wired in parallel to the
Input connector and transmits the unbuffered source
signal even when the Acheron is powered off.
To avoid distortion when looping multiple Acherons, 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 peak SPL
over the entire operating bandwidth of the loudspeakers.
Most professional audio equipment can transmit these
source levels.
To calculate the load impedance for the looped loudspeak-
ers, divide 10 kOhms (the input impedance for a single
Acheron) by the number of looped loudspeakers. For exam-
ple, the load impedance for 10 Acheron loudspeakers 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 Acheron loudspeakers with other self-pow-
ered Meyer Sound loudspeakers and subwoofers.
Acheron Audio Connectors, Input and Loop Output