Trupower Limiting - Meyer Sound LINA Operating Instructions Manual

CHAPTER 3: AMPLIFICATION AND AUDIO CONNECTORS
Pins 2 and 3 carry the input as a differential signal. Pin 1 is
connected to earth through a 1 k
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 the loudspeaker produces unwanted noise
or hiss, disconnect its input cable. If the noise
stops, there is most likely nothing wrong with the loud-
speaker. To locate the source of the noise, check the
source audio, AC power, and electrical 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 19). For applications that require
multiple LINAs, connect the Loop output of the first loud-
speaker 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 imped-
ance of the looped loudspeakers. In addition, the source
device must be capable of delivering approximately 20 dBV
Ω ) to yield the maximum SPL over the
(10 V rms into 600
operating bandwidth of the loudspeakers.
To calculate the load impedance for the looped loudspeakers,
divide 10 k Ω (the input impedance for a single loudspeaker) by
the number of looped loudspeakers. For example, the load
impedance for 10 LINAs is 1000
number of looped loudspeakers, the source device should
have an output impedance of 100
applies when looping LINAs with other Meyer Sound self-
powered loudspeakers.
NOTE: Most source devices are capable of
driving loads no less than 10 times their output
impedance.
20
Ω , 1000 pF, 15 V clamped
Ω (10 k Ω / 10). To drive this
Ω or less. This same rule
TIP: Audio outputs from Meyer Sound's loud-
speaker GALAXY Network Platform have an out-
put impedance of 50 ohms. Each output can drive up
to 20 Meyer Sound (10 k
tortion.
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.

TRUPOWER LIMITING

LINA employs Meyer Sound's advanced TruPower
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 the source material changes
and as thermal values for the loudspeaker's voice coil and
magnet vary. Consequently, conventional limiters often
begin limiting prematurely, which reduces system headroom
and dynamic range.
In contrast, TruPower limiting anticipates varying driver
impedances by measuring both current and voltage to com-
pute the actual power dissipation in the voice coil. This
approach improves performance, both before and during
limiting, by allowing the driver to produce the maximum SPL
across its entire frequency range, while also retaining signal
peaks. TruPower limiting also eliminates power compres-
sion at high levels over lengthy periods, which helps regu-
late voice coil temperatures, thereby extending the life of the
driver.
Ω ) loudspeakers without dis-
®
limiting.