Have you ever heard booms going through the temperature change after
sunset? Might be more likely a time that my night class can explore.
Rob D.
>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.
>>
> > = = ==
>>
>>
>>
>>
>>
>> --
>
>
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
________________________________________________________________________
________________________________________________________________________
|