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CHAPTER 3: AMPLIFICATION AND AUDIO
16
NOTE: Most source devices are capable of
driving loads no smaller than 10 times their
output impedance.
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.
LIMITING
Acheron loudspeakers employ Meyer Sound’s advanced
TruPower
®
limiting. Conventional limiters assume a constant
loudspeaker impedance and set the limiting threshold by
measuring voltage alone. This method is inaccurate
because loudspeaker impedances change as frequency
content in the source material changes, and as thermal val-
ues for the loudspeaker’s voice coil and magnet vary. Con-
sequently, conventional limiters often begin limiting
prematurely, which reduces system headroom and dynamic
range.
In contrast, TruPower limiting anticipates varying loud-
speaker impedances by measuring both current and voltage
to compute the actual power dissipation in the voice coil.
This improves performance, both before and during limiting,
by allowing the driver to produce the maximum SPL across
its entire frequency range. TruPower limiting also eliminates
power compression at high levels over lengthy periods,
which helps regulate voice coil temperatures, thereby
extending the life of the driver.
NOTE: Since TruPower limiting only reduces
signal levels to keep voice coil temperatures
under a safe margin, signal peaks remain unaffected.
Limiting LEDs
Behavior for the Acheron Limit LEDs is described below:
■ The low- and high-frequency drivers for the Acheron 80
and Acheron 100 are powered by separate amplifier
channels, each with their own limiter. Limiting activity is
indicated with a High Limit LED for the high-frequency
channel, and a Low Limit LED for the low-frequency
channel.
■ The two low-frequency drivers for the Acheron LF are
powered by separate amplifier channels that are routed
to a single limiter. When a safe power level is exceeded
in either channel, limiting is engaged for both channels
and the Low Limit LED lights.
When engaged, the limiters not only protect the drivers but
also prevent signal peaks from causing excessive distortion
in the amplifier channels, thereby preserving headroom and
maintaining smooth frequency responses at high levels.
When levels returns to normal, below the limiter thresholds,
limiting ceases.
The Acheron performs within its acoustical specifications at
normal temperatures when the Limit LEDs are unlit, or if the
LEDs are lit for two seconds or less and then turn off for at
least one second. If the LEDs remain lit for longer than three
seconds, the loudspeaker enters hard limiting where:
■ Increases to the input level have no effect.
■ Distortion increases due to clipping and nonlinear driver
operation.
■ The drivers are subjected to excessive heat and excur-
sion, which will compromise their life span and may
eventually lead to damage over time.
CAUTION: The Limit LEDs indicate when a
safe, optimum level is exceeded. If the
Acheron 80s or Acheron 100s in a system begin to
limit before reaching the required SPL, consider add-
ing Acheron LFs to the system (see Chapter 4, “Inte-
grating Acheron LF Loudspeakers”).
NOTE: Acheron loudspeakers use optical limit-
ers that add no noise and have no effect on the
signal when the limiters are not engaged and the
Limit LEDs are not lit.
Acheron Limit LEDs
!
!