Hi Ralf,
It's not me that's building a capsule, it's michaeljtbrooks.
However, I can make some comments:
"2- the backplate cannot be stiff enough. That is one reason
for partial cancelation of higher frequencies. This is because
if it is not it will probably cancel out frequencies by slightly
moving by soundpressure in the opposit direction of the
membrahne."
I'm not convinced. The backplate would need to be very flexible to
react in such a way. Most of the backplates are made of a piece of
metal (often brass) that is millions of times heavier and more
rigid than the diaphragm.
"3- the backplate had to be fairly thick so that you can make
some sackholes in it for damping ?reasons "
Indeed, blind holes (as well as through-holes) are necessary for
providing damping of the diaphragm
Le 12/04/2022 ¨¤ 12:38, Ralf Falk a
¨¦crit?:
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Hey, Jerry Lee,
my namens Ralf and this is the first reply ?in
this forum. I¡® m writing from Germany so please ? ? excuse my
bad language.
About 10 years ago I made a very similar
experiment wich I stopped as I got me a lath to work with. I
found out the same things that you posted here and came to the
following conclusions:
1- It is important to get the membrahn streched
the same degree to all sides?
2- the backplate cannot be stiff enough. That is
one reason for partial cancelation of higher frequencies. This
is because if it is not it will probably cancel out frequencies
by slightly moving by soundpressure in the opposit direction of
the membrahne.
3- the backplate had to be fairly thick so that
you can make some sackholes in it for damping ?reasons?
4- to get rid of most of the parasitic
capacitance, you simply should take of the copper of your
backplate piece in the airia where the frame that holds your
membrahn will be positioned?
I hope that this will bring you in a good
direction.
Good luck?
I'm pretty suspicious of the
membrane resistance which is a few ohms per cm2 as the
culprit. So any suggestions for more conductive
aluminiumised Mylar would be greatly appreciated!
Whatever few ohms there don't matter compared to the
Gigaohm input resistance of the Alice circuit.
Look elsewhere. Surely 20 micron thickness does not help
with sensitivity, but all the parasitic capacitances are
probably the main culprit.
