> There are places in shopping malls and factories and such where dodgy
> acoustics cause the infrasound from the A/C ducts to sum. Standing there


Used to live near a shunting yard.
Normally no problems.

In winter about ?4am they used to run up two diesel locos at once (maybe
more?) in an engine shed nearby. Presumably these were on governors set to
idle at the same speed. The multiple engines used to "beat" (possibly
resonating the building they were in) and produce a loud slow
woomp-a-woomp-a-woomp for about 15 minutes. Presumably they were warm after
that ?



        RM

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