Nexo 45N Monitor - Manual (Page 12)

Page 12/26 A MPLIFIER S ELECTION FOR USE WITH 45 N-12
- measure the voltage at the output of the amplifier
- calculate the gain using the formula Gain = 20 * LOG10(Vout/Vin).
Some examples:
Vin / Gain 20dB 26dB 32dB 37dB (1.4V sensitivity / 1350Wrms)
0.1 V 1 V 2 V 4 V 7.1 V
0.5 V 5 V 10 V 20 V 35.4 V
1 V 10 V 20 V 40 V 70.8 V
Remember that constant sensitivity settings will give a different gain value when the amplifier power is
different.
NEXO recommends 26 dB gain amplifiers, as it is at the same time adequately low and quite common
amongst amplifier manufacturers. This gain setting improves signal to noise ratio and allows all
preceding electronic equipment, including the NX242-ES4 TDcontroller, to operate at optimum level.
Using a high gain amplifier will raise the noise floor proportionally.
Operating Mode
Most two channel amplifiers available on the pro-audio market have the following operating modes:
Stereo: two fully independent channels deliver identical power into identical loads
NEXO recommends Stereo Mode for all amplifier channels feeding 45°N-12 monitors.
Bridge-Mono: the second signal channel processes the same input as the first channel, but with
reversed phase. The (single) load is connected between the two positive channel outputs using a
suitable connection. While the total output of the amplifier remains the same, the available output
voltage, the minimum impedance that can be connected and the voltage gain are doubled as compared
with stereo operation. Typically, only channel 1 input is active. Positive and negative output connections
vary depending on amplifier manufacturers.
NEXO does not recommend Bridge Mono Mode unless amplifier power is clearly not sufficient.
IMPORTANT
When in Bridge-Mono mode, check your amplifier user manual for proper connection of
outputs 1(+) and (2+) in relation to input phase.
Parallel-mono: the output terminals of the two channels are configured in parallel using an internal relay.
The (single) load is connected either to the output of channel 1 or to that of channel 2 (as if in stereo).
While the total output of the amplifier remains the same the output voltage level is also the same as in
stereo mode. The minimum impedance that can be connected is reduced by half due to the fact that
current capability is doubled. Typically, only channel 1 input is active.
NEXO does not recommend Parallel-Mono Mode for any PS Series speaker amplification.
Warning on amplifiers signal processing features
Some high-end amplifiers may include signal processing functions similar to those found in the NX242
TDcontroller ("loudspeaker offset integration", "limiter", "compressor," etc.). Moreover, when this
processing is digital, computation latency time can introduce a few milliseconds delay from input to
output. These functions are not adapted to specific system requirements and may interfere with the
complex protection algorithms used in the NEXO TD Controllers.
NEXO do not advise using other protection systems in conjunction with the NEXO TD Controllers and
they should be disabled.
IMPORTANT
For proper system protection, no latency time or non-linear devices should be
introduced between the output of the NEXO TDcontroller and the input of loudspeakers
through use of DSP modules such as internal amplifier signal processing.