Martinsound MonitorMAX, User Manual, Page: 11 / 14

Calibrating MonitorMAX
The default SPL displayed on MonitorMAX comes set to 50dB on power up. However, this is not the intended
operating level, but only a safe starting point. Once the unit has been set up, a new default SPL can be
programmed by the user. When MonitorMAX has been properly calibrated, the display will indicate the actual
SPL reference as adjusted by the Monitor level control in 1dB increments. Since 85dB SPL is the accepted
working standard for film mixing stages, this reference is normally used as the target to calibrate MonitorMAX.
To achieve the cleanest audio path with the best signal-to-noise ratio, it is recommended to run all signals at
line level (+4dBu nominal) and take as much attenuation at the end of the audio chain (e.g. the speaker
amplifier inputs) as necessary to achieve the desired SPL. When MonitorMAX is set to the default display
range of 40 to 100dB, a Monitor level setting of 85dB SPL reflects 15dB of attenuation to the outputs.
Likewise, a Monitor level setting of 100dB reflects unity gain from inputs to outputs. When calibrated to this
setting, MonitorMAX will provide a wide range of level control with a maximum SPL of 122dB (if the speakers
will handle it) while maintaining a good signal-to-noise balance.
Simply stated, proper calibration is when a +4dBu input signal (ideally wide band pink noise) produces an
85dB reading on an SPL meter at the listening position, when the MonitorMAX level control is set to 85dB.
The best way to accomplish this is to first set the input controls on your power amplifiers to the lowest level
(most attenuation) and set the MonitorMAX level control so the display reads 85.
Note: If using Powered Monitors or amplifiers that do not provide a wide range of input attenuation, it
may be necessary to use the internal trim adjustments on the MonitorMAX “Levels” menu to obtain
the required amount of attenuation. Again, for best results take as much attenuation as possible at
the amplifier inputs.
Select a Monitor Input (1 – 8) and feed a +4dBu pink noise test tone into either side (L or R). A metering
device can be connected to the Meter outputs (1-2) of MonitorMAX to confirm the +4dBu reading. Place an
SPL meter (Radio Shack model or equivalent, C weighted, slow response) in the listening position and adjust
the corresponding amplifier input control until approximately 85 dB is read on the SPL meter. Repeat the
procedure for other speakers.
Note: It may be necessary to use the internal speaker trims on the MonitorMAX “Levels” menu to
obtain precise adjustments for each speaker including Cue and Alt L & R. These trims provide up to
20dB of attenuation in 0.1dB increments.
In addition to the default SPL range of 40 –100dB, 4 other SPL display ranges are included in the “Mon
Interfaces” menu. Changing the range does not effect the electrical signal path, but determines where the
calibration target (85dB) lies in relation to the top of the display range. This will effect the way the unit is
calibrated, in that
more or less attenuation will have to be taken elsewhere (trims or amplifier inputs) to
compensate for more or less attenuation taken in the Monitor Level control. The object is to obtain the best
signal-to-noise ratio while retaining adequate SPL headroom.
If an SPL meter and pink noise source is not available, the unit should be set up by ear. First set the
MonitorMAX Level control to 85dB and then adjust the amplifier input levels to a comfortable working level.
This should be adequate for many applications where the SPL reference is not critical.
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