Your comments sound right. I would suggest a further theory as well.
As you recall ice expands as it gets colder and contracts as it warms
which is reverse of most things.
The extreme first cold causes the ice to build fast over a body of
water that is actually still above freezing as an average. As it
builds fast many crashes can be heard. The next day when the sun
warms the ice sheet in these cold temps the bottom of the sheet
contracts first causing the pings or star wars like sounds. There
are also crashes that occur during this time as well.
The crashes I suspect are the shifts and cracks starting at the top
of the ice sheet or through the entire sheet and they go well above
2,500 cycles. The more interesting pings are the contraction cracks
originating from only the bottom side of the sheet and are mainly
below 600 cycles.
I suspect the more extreme the temperature of the ice to the water
the more the activity will be as the sun warms the sheet the next
day. This would explain why it is best only on one day and why it
isn't great every year.
A very small, short ping download
http://home.comcast.net/~richpeet/ice.mp3
Rich
The conditions you
> describe Rich are very consistent with the day I
> encountered them. Larger, deep lake, clear day,
> clear ice, steady radiation and by early
> afternoon some surface cracks forming. Separate
> from these surface cracks were spatially
> dispersed, harmonic "pings" that ricocheted and
> tended to cluster around intervals about 5-20
> minutes apart. My wild guess is the unusual
> sonic qualities come from floating surface layer
> of ice reacting very much like a speaker membrane
> or drumhead to concussions either from direct ice
> strikes or fairly large fractures in deeper
> layers of ice. ...
> Milwaukee. Rob D.
>
> = = ==
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> --
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