Interference between two monitors placed side-by-side can cause images on
the monitors to vibrate. The reason is that, when placed side-by-side,
monitors can magnetically interfere with each other, causing the image on
one or both monitors to appear to vibrate slightly. This interference
problem is most often seen when an RGB color monitor is placed next to a
large-screen monochrome monitor. The amount of interference can also vary
depending on the user's environment.
Moving the monitors further apart, especially the rear ends, usually
reduces the vibration effect.
Technical Reason For Picture Vibratrating
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The cause of this shimmering effect lies in the vertical refresh rate, the
number of times a monitor repaints the screen each second. When this rate
differs significantly between monitors, the interference described above
can occur. There is often a large difference between RGB and monochrome
monitors. Thus, the vibration effect most often occurs with this
combination. Because other factors are involved, it is possible for two
monitors with the same refresh rate to exhibit this effect, although this
is less frequent.
Shielding monitors so as to prevent this type of interference would add a
great deal to the cost of each monitor. Further, by shielding a monitor
you can prevent the monitor from interfering with other monitors, but other
monitors could still interfere with it. Apple is investigating a number of
technologies to prevent this interference in the future and plans to
incorporate them as they become feasible.