Meyer Sound 100, 80, LF LIMITING, Limiting LEDs

CHAPTER 3: AMPLIFICATION AND AUDIO

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

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