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Re: water resistant, acoustically transparent fabric

Subject: Re: water resistant, acoustically transparent fabric
From: "James Shatto" wwwshadow7
Date: Sun Sep 10, 2017 8:41 pm ((PDT))
You might be over looking the obvious.=A0 It's not uncommon to use unlubric=
ated condoms as rain protection for pro-level mics.=A0 Once you're past the=
 initial XLR you can have more sheltered enclosures without affecting the s=
ound much.=A0 Nylon is great for deflecting wind, while still allowing some=
 air flow, not so great when the air is all water.=A0 Or the wind is extrem=
e.
- James
    On Sunday, September 10, 2017, 8:19:28 PM CDT,  =
[naturerecordists] <> wrote: 

 =A0  
Hi Russ, and all,=A0

Florian here. I'm new to pure audio recording, but enjoy it. I am not new t=
o paying attention to the preservation of ecosystems. I live in NYC.=A0
I choose to post now because I have one broad solution, and one specific so=
lution to this problem which I don't see mentioned.
(TBH, the yahoo groups message format, archives, and delivery schedule, rul=
es, confuses. Apologies if I breach protocol, and thanks to anyone who corr=
ects me.)
(Also, I am NOT a scientist or engineer)
This sounds like a budget project. Which is awesome. I DIY as much as I can=
, too. Unfortunately I'm not sure the ideas I have are cost-sensitive. I've=
 never tried them, but I know for a fact one of them is in ubiquitous use b=
y microphone manufacturers. Even if they are not helpful to you, Russ, whos=
e project is already completed I'm sure,=A0I figure since there have been m=
any responses and no one has brought these up, it may benefit someone inter=
ested in waterproofing, windproofing, and weatherproofing microphones and a=
rrays.=A0
1) Parylene coating
I'll start with the specific one first.=A0
...instead of weatherproofing the enclosure, you could waterPROOF the capsu=
le.=A0
Parylene is, well, here:=A0https://en.wikipedia.org/wiki/Parylene=A0I'm not=
 a doctor.=A0
The great thing about parylene is that very very, verrrrrry thin coatings o=
f it can be made on a substrate. Parylene is commonly used to coat lavalier=
 membranes and sometimes the entire capsule or assembly. This protects agai=
nst sweat, and hydrophones sometimes have a parylene coating too. The stuff=
 once properly applied (not so easy) has excellent mechanical properties fo=
r the application, the quality and quantity of motion of the membrane is ch=
anged, but not much, and if the coating and assembly are done in such a way=
 the element should withstand repeated direct blows from raindrops or even =
jets of water.=A0
If you search "Parylene coating" you'll find like a million businesses whic=
h offer this as a service product, alongside many other forms of gas deposi=
tion and sputtering. For a single microphone, the cost is unlikely to be re=
asonable, but who knows.=A0

2) Hydrophobic mesh
You mention "water resistant" rather than waterproof. So, air (pressure wav=
e) in, water (droplets) out.=A0
I wonder about wrapping in a hydrophobic mesh. Have you heard about these? =
If not you might want to alphabet-google it, and even then you'll get a lis=
t of suppliers who usually only sell to companies rather than individuals w=
ith the exception of this: http://www.ebay.com/itm/like/181254139613?chn=3D=
ps&dispItem=3D1=A0. Not to be confused with "mesoporous hydrophobic" solids=
/materials.=A0
The concepts of droplet contact angle, wettability of a substrate (upon whi=
ch a droplet comes to rest/stops), and pressure, influence their design.=A0
Because H20 has reasonable surface tension, droplets of H20 exhibit varying=
 degrees of wettability of a given substrate they rest on (with or without =
earth gravity). Contact angle is more or less the measurement of the deviat=
ion from a perfect spherical formation of a droplet on a substrate. Rarely =
happens.=A0
anyways, if you create a mesh of thin wires of a material with a large cont=
act angle in respect to H20, like teflon/PTFE, which is superb, when the nu=
mber of wires per given area reaches a certain density, and the size of the=
 areas where the wires are not, the pore size, shrinks to an area which is =
at or beyond the contact angle equilibrium, droplets of water can't get thr=
ough at a given size and pressure. They skitter about and away. Shrink the =
pore size too much and air can't get through either. Shrink them even more =
and you wind up back in the zany world of mesoporous functional materials, =
which actually separate or ab/dsorb large molecules from small molecules on=
 the, like, molecular level, dude.=A0
What you'd want is a pore size and a material which is a goldilocks, just r=
ight, size - so that the occlusion of water is maximized, and the attenuati=
on of acoustic waves in air is minimized and as spectrally linear as possib=
le. (I should also say that this isn't 100% waterproof. Plunge this deep en=
ough underwater and water gets in, or if the water droplets are smaller tha=
n the pores or have ballistic velocities or whatever)
I have not tested and have no knowledge of how good or bad an air interface=
 mesh might be in terms of sonic alteration, though a quick search of a-g p=
atents leads me to believe they are widespread in small diaphragm mics in h=
earing aids and other in-ear applications.=A0
And even if they do alter, that's what EQ is for. Right?
-Florian

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