and while i'm out of lurk mode...
i posted this question to the phonography list, but got no response, so
i thought i'd try here. any thoughts about this?
i've been fiddling with building a simple hydrophone for awhile now.
i'd made several attempts with hollow cavities filled with vaseline,
poster tack, oil, or nothing. i'd read that a hydrophone ought to be
filled with oil, something about it having a similar density to water
and therefore letting the soundwaves travel through the cavity to the
piezo inside. working with oil is messy, however, and it's very
difficult to reliably seal the cavity without any air bubbles inside. i
managed one though, but i also had an identical one which i'd sealed
with an empty cavity. i compared them, and both work great, and sound
remarkably similar, if not identical. so what i wonder is: why do i
think the cavity needs to be full of oil? what does that provide that
my empty one does not have? anyone have any insight?
best,
patrick
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