A
MPLIFIER SELECTION FOR USE WITH
RS15
Page
19/58
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In cases where you don't know the gain of your amplifier (or want to check it) please follow this
procedure:
1) Unplug any loudspeakers from the amplifier outputs
2) With a signal generator, feed a sine wave at 1000Hz at a known voltage (say 0.5V) to
the input of the amplifier under test
3) Measure the voltage at the output of the amplifier
4) Calculate the gain using the formula Gain = 20 * LOG
10
(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 low gain amplifiers: +26dB is recommended, 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 TDcontroller or GEO S12
TDController, to operate at optimum level. Remember that 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:
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Stereo: two fully independent channels deliver identical power into identical loads
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NEXO recommends Stereo Mode for all amplifier channels feeding RS15’s.
•
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 RS15 amplification.
Warning on amplifiers signal processing features
Some high-end amplifiers may include signal processing functions similar to those found in the NX242
TDcontroller or in GEO S12 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 NX242.
