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CHAPTER 3: AMPLIFICATION AND AUDIO
14
To calculate the load impedance for the looped loudspeak-
ers, divide 10 kOhms (the input impedance for a single
JM-1P) by the number of looped loudspeakers. For exam-
ple, the load impedance for 10 JM-1P 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 JM-1P loudspeakers with other self-powered
Meyer Sound loudspeakers and subwoofers.
NOTE: Most source devices are capable of
driving loads no smaller than 10 times their
output impedance.
NOTE: 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 loudspeakers in a
system have reversed polarity, frequency response
and coverage can be significantly degraded.
Limit LEDs
The low- and high-frequency drivers for the JM-1P are pow-
ered by separate amplifier channels, each with their own
limiter. Limiting activity is indicated with the two yellow Limit
LEDs. The top LED indicates limiting for the high-frequency
channel and the bottom LED indicates limiting for the low-
frequency channel. When engaged, a channel’s limiter not
only protects the driver, but also prevents signal peaks from
causing excessive distortion in the amplifier’s channel,
thereby preserving headroom and maintaining smooth fre-
quency responses at high levels. When a channel’s level
returns to normal, below the limiter’s threshold, limiting
ceases.
The JM-1P 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 an LED remains lit for longer than three
seconds, that channel enters hard limiting where:
Increases to the input level have no effect.
Distortion increases due to clipping and nonlinear driver
operation.
The driver is subjected to excessive heat and excursion,
which will compromise its life span and may eventually
lead to damage over time.
CAUTION: The Limit LEDs indicate when a
safe, optimum level is exceeded. If a JM-1P
loudspeaker begins to limit before reaching the
required SPL, consider adding more loudspeakers to
the system.
NOTE: The JM-1P loudspeaker uses optical
limiters that add no noise and have no effect
on the signal when the limiters are not engaged and
the Limit LEDs are not lit.
On/Temp LED
When the JM-1P is powered on, its On/Temp LED turns
green. If the temperature of the heat sink reaches 85° C
(185° F), the On/Temp LED changes from green to red and
the limiter threshold is lowered to a safe level to prevent the
system from overheating. Under high temperature condi-
tions the output level is reduced by approximately 6 dB.
When the heat sink temperature decreases to 80° C
(176° F), the On/Temp LED changes from red back to green
and the limiter threshold returns to normal.
NOTE: When the On/Temp LED is red, this is
an indication that the unit is reaching its maxi-
mum dissipation and a reduction in SPL is recom-
mended.
TIP: When the JM-1P is connected to an RMS
network, the RMS software provides additional
feedback on the loudspeaker’s operating tempera-
ture. For more information, see Chapter 6, “The RMS
Remote Monitoring System.”
Limit LEDs
High-frequency limiter LED
Low-frequency limiter LED
!