This electret was made of a 75mm diameter mix of D'Addario dark rosin (27 grams),
carnuaba wax (38.2 grams) and beeswax (1.4 grams). I chose this rosin simply
because it was what was available, though I was aware that lighter is better
and water white rosin (which was not available) is best. The box says it is
triple-filtered and contains non-crystallizing American gum rosin, natural beeswax
and castor bean oil.
The top electrode
was 50mm so the effective area should be around that. This electret was
made using the technique outlined on the main
electret page.
Note: This electret was made, wrapped and put on the shelf on July 31, 2006.
It won't be unwrapped until a month from there so check back later to see
if it worked.
Making the Electret
Available at music stores. Used for putting on violin bow strings
and other places.
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The beeswax, purchased locally.
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The three ingredients before melting.
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I turned on the stove to MED at 4:30pm. Wax temperature quickly rose to 160C
so I turned the stove off again. By 4:45pm the wax was at 100C so I heated up
the top electrode using a heat gun and put it in place. I turned on the
high voltage power supply and
set it for 6kV. Initially the oscilloscope showed some low amplitude spiking
though there were no arcs and no sounds. After about 1 minute the spiking was
gone. While the electret was still cooling, the voltage kept going up slowly
so I kept turning it back down to 6kV. It looked solid by 5:00pm but I didn't
turn off the power supply until 5:22pm. The bottom of the aluminium bowl was
a little warm. I couldn't easily dettach the top electrode so I left it attached
and wrapped up the electret.
