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This is a fit for something I want to make.

I want to make a mic for tracking wildlife. I want to make it so you can hear the
faintest, furthest away sounds. Anotherwords, I want to crank the gain up to
infinity and beyond and I DON'T want to hear transistor hiss.

I want to use a 6mm mic case and I have 3 volts from batteries to work with. I
want to use an onmi first.

I am not familiar with RF mics. Is this an application best tried as an RF mic?
Also if I have to have the capsule 6 inches away from the PCB, is this going to
be a problem?

If we want to try this as an RF thing, this may be useful; I have a friend around
the corner that owns a big time RF testing facility. I can get him in on this too if
that brings anything helpful to the project. He's one of those crew cut, slide
rule, short sleeve shirt, 60's NASA type guys, who has designed tons of DOD
RF stuff.

So what's the concept of the RF mic and is this the way to go for MAXIMUM
low noise and high gain? What needs doing to make it work?

--- In micbuilders@..., "mstrong82" <mstrong@j...> wrote:

This is a fit for something I want to make.

I want to make a mic for tracking wildlife. I want to make it so

you can hear the

faintest, furthest away sounds. Anotherwords, I want to crank the

gain up to

infinity and beyond and I DON'T want to hear transistor hiss.

I want to use a 6mm mic case and I have 3 volts from batteries to

work with. I

want to use an onmi first.

One problem, IMHO, with the panasonics is the size of the hole in the
front. It is too small and can reverberate under extremely loud sound
pressure levels.

If you can make something with a larger diameter hole it would be great.

Darren

mstrong82 wrote:

This is a fit for something I want to make.

I want to make a mic for tracking wildlife. I want to make it so you can hear the
faintest, furthest away sounds. Anotherwords, I want to crank the gain up to
infinity and beyond and I DON'T want to hear transistor hiss.

Ah, but therein lies the rub. From looking at noise specs
for various size mics, from the experiments of one of our
members, and according to:




it seems that self noise has a large component that is
molecular shot noise from thermally agitated air molecules
impinging on the diaphragm which can only be reduced by
increasing the diaphragm diameter. A fairly simple argument
shows that increasing the diameter has the effect of
averaging that noise down relative to the signal.

A definitive experiment would be to compare the self noise
of a small electret at various air pressures, including a
near vacuum, which wouldn't be all that difficult if anyone
had a bell jar and a hand vacuum pump.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

it seems that self noise has a large component that is
molecular shot noise from thermally agitated air molecules
impinging on the diaphragm which can only be reduced by
increasing the diaphragm diameter.

Or adding more diaphragms. Two mics, twice the signal, noise
goes up by 1.4.

Andrew Burgess wrote:

it seems that self noise has a large component that is
molecular shot noise from thermally agitated air molecules
impinging on the diaphragm which can only be reduced by
increasing the diaphragm diameter.

Or adding more diaphragms. Two mics, twice the signal, noise
goes up by 1.4.

Right. Either approach begins to degrade high frequency
performance due to coincidence considerations. I'm not sure
which is easier to manage.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

--- dnemeth01 <dnemeth01@...> wrote:

One problem, IMHO, with the panasonics is the size of the hole in the
front. It is too small and can reverberate under extremely loud
sound
pressure levels.

If you can make something with a larger diameter hole it would be
great.

Darren

Depending on your definition of "larger," you can cut the fronts of
entirely fairly easily. I suppose it would be possible to drill a
larger hole in some thin aluminum and glue the part back on, but that
might be tricky.

I've got pictures of the modded capsule, and an a/b type of
comparision. at www.2fiddles.com . I've made some recordings with the
modded capsule, and bass response is way down. I haven't actually done
anything with the recordings to see if they will be useful or not.

Bob


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Bob Rogers wrote:

Depending on your definition of "larger," you can cut the fronts of entirely fairly easily. I suppose it would be possible to drill a larger hole in some thin aluminum and glue the part back on, but that might be tricky.

Actually as capsules are made of quite thin aluminum, you can
easily cut hole larger with sharp scalpel (which will not be so
sharp after performing this mod).

Indrek

--
Indrek Rebane | Borthwick-Pignon
Electronics Engineer | Tartu Science Park
Phone: (+372) 7 302 641 | Riia 185, 51014 Tartu
Fax: (+372) 7 383 041 | Estonia
indrek@... | www.bps.co.ee

--- Indrek Rebane <indrek@...> wrote:

Bob Rogers wrote:

Depending on your definition of "larger," you can cut the
fronts of entirely fairly easily. I suppose it would be
possible to drill a larger hole in some thin aluminum and glue
the part back on, but that might be tricky.

Actually as capsules are made of quite thin aluminum, you can
easily cut hole larger with sharp scalpel (which will not be so
sharp after performing this mod).

Indrek

Have you done that? There's not a lot of clearance between the face and
the diaphragm. I don't think I would have much luck doing that sort of
thing, because my hands aren't steady enough.

I'd also have a problem making the new hole a circle, I think. I have a
hard time just trying to draw a circle ;-) I wonder what effect a non
circular hole would have on the sound.

I suppose you would need to be really careful to avoid getting little
bits of metal between the face and the diaphragm too.

Bob


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Bob Rogers wrote:

Actually as capsules are made of quite thin aluminum, you can
easily cut hole larger with sharp scalpel (which will not be
so sharp after performing this mod).

Have you done that? There's not a lot of clearance between the
face and the diaphragm.

Only on dead microphones, have had no need to do such modification
in past.

Indrek

--
Indrek Rebane | Borthwick-Pignon
Electronics Engineer | Tartu Science Park
Phone: (+372) 7 302 641 | Riia 185, 51014 Tartu
Fax: (+372) 7 383 041 | Estonia
indrek@... | www.bps.co.ee

dnemeth01 wrote:

One problem, IMHO, with the panasonics is the size of the hole in the
front. It is too small and can reverberate under extremely loud sound
pressure levels.

If you can make something with a larger diameter hole it would be great.

Someone here, I think perhaps it was Seigfried back when he
was a contributer, calculated the resonance of the Helmholtz
resonater that the cavity and hole comprise and found it to
be well above the audio band. Enlarging the hole could even
possibly lower it.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

dnemeth01 wrote:

One problem, IMHO, with the panasonics is the size of the hole in the
front. It is too small and can reverberate under extremely loud sound
pressure levels.

If you can make something with a larger diameter hole it would be great.

Bob Cain wrote:

Someone here, I think perhaps it was Seigfried back when he
was a contributer, calculated the resonance of the Helmholtz
resonater that the cavity and hole comprise and found it to
be well above the audio band. Enlarging the hole could even
possibly lower it.

Larger hole == higher resonance; smaller hole == lower resonance frequency.
Diffraction effects might have more influence on HF performance -- dunno.

-- Mike

Mike Feldman wrote:

Larger hole == higher resonance; smaller hole == lower resonance
frequency.
Diffraction effects might have more influence on HF performance -- dunno.

Mike, I don't have the equations in front of me but, IIRC,
the resonant frequency is a convex function of port
diameter. i.e. there is a diameter at which it is minimum
and going either larger or smaller makes it higher. Or
perhaps there is a maximum and going either way makes it
lower. Anybody know the equation?


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

when i was using really cheap capsules (abut 10 cents each in india), i used to grind off the front plate, very carefully, and it improved the hf response of the 6 mm capsules i was using. never tried with the smaller panasonics.

most of the more expensive capsules do not have this single whole. the sennhseiser mk 02 s have some kind of raised dimple in front, with four really small holes. the tram if i remember has a tiny piece of metal mesh.

the panasonic way of making the capsule is actually one of the simplest. deep draw the cans, drop all the pieces in in the correct order, and crimp the edge.

somebody should just make a new body constructred out of turned parts for the panasonic insides - one metal ring, one diaphragm, one plastic ring, backplate, fet (?) with gate welded to backplate, and a plastic support. - i would keep the plastic support, because then you need to make only two or three turned metal parts. anybody ready ?

umashankar

dnemeth01 wrote:

One problem, IMHO, with the panasonics is the size of the hole in the
front. It is too small and can reverberate under extremely loud sound
pressure levels.

If you can make something with a larger diameter hole it would be great.

Someone here, I think perhaps it was Seigfried back when he
was a contributer, calculated the resonance of the Helmholtz
resonater that the cavity and hole comprise and found it to
be well above the audio band. Enlarging the hole could even
possibly lower it.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

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Bob Cain wrote:

Anybody know the equation?

Explains it all clearly. Simplifying equation for microphone
construction:

f = (v*R_h)/(2*pi*R_c*sqrt(H_h*H_c)

where:
v - speed of sound
R_h - radius of hole
R_c - radius of cavity
H_h - height of hole
H_c - height of cavity

So larger the diameter, higher the frequency. Having multiple
small holes should be equal to condition of having a large hole
with area equal to sum of the areas of small holes.

Indrek

--
Indrek Rebane | Borthwick-Pignon
Electronics Engineer | Tartu Science Park
Phone: (+372) 7 302 641 | Riia 185, 51014 Tartu
Fax: (+372) 7 383 041 | Estonia
indrek@... | www.bps.co.ee

Indrek Rebane wrote:

Bob Cain wrote:

Anybody know the equation?

Explains it all clearly. Simplifying equation for microphone
construction:

f = (v*R_h)/(2*pi*R_c*sqrt(H_h*H_c)

So it is monotonic in R_h in its simplest form. I stand
corrected.


Thanks,

Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein