In article .com,
Peter Bennett wrote:

Yes - actually, a piezoelectric crystal that vibrates at the operating
frequency.

True, actually 90% of the piezoelectric crystal tranducers are Barium
Titanate Crystals and most of these are made by one company. (I forget
the name now, but they OEM to all the Sounder producers) The 28Khz
Transducers are Magnetic Restriction types and not crystals, and the old
WWII SubSignal "Big Whoppers" were also Magnetic Restriction types as
well. It's really hard to get crystals to resonate below 50Khz with the
power levels used by typical sounders below that frequency.

Bruce in alaska
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