There is no loud audible whine if any. This is where proper filtering comes
in and why 400 was used in the first place; you can make power supplies much
smaller, less to radiate audible noise. If you hear any real audible whine,
you have (a) problem/problems. A huge building that uses a room full of
switchgear will have a very mild hum from 60 HZ. 400 will reduce that
significantly. There had better not be ANY whine of any sort in ANY
aircraft transmissions as it is easily filtered out! What you may be
hearing is the whine of the jet engines. There really is no drawback to
using 400 HZ other than it is not available for common use and perhaps more
expensive to produce. (Julian Burke)
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