Microphone Science Project?

M

Magoo

Guest
I'm looking for some info on building a microphone out of scrap materials
as a science project. I've googled it but didn't find anything really good.

Anyone know of a page that describes how to build microphone from scratch?
Or maybe you have some tips of your own?
 
Magoo wrote:
I'm looking for some info on building a microphone out of scrap materials
as a science project. I've googled it but didn't find anything really good.

Anyone know of a page that describes how to build microphone from scratch?
Or maybe you have some tips of your own?
Click to expand...
A dynamic microphone is essentially a tiny speaker.
a speaker has a permanent magnet in an iron core designed to produce a
radial field (outward across a circle) in a circular air gap. The
diaphragm that moves when air vibrations hit it has a small coil
attached to it that sits in the air gap. When the wires move back and
forth across the magnetic field, voltage is produced in the wire. If
current is passes through the wire, the coil produces force on the
diaphragm.

http://www.thespeakerstore.com/glossary/howspeakerswork.htm
http://howstuffworks.lycoszone.com/speaker2.htm
There are also microphones based on other energy conversion
principles:
http://electronics.howstuffworks.com/question309.htm

For a simple home made version of the dynamic mic, it might be easier
to mount a stationary coil and move the magnet in and out of it with
the diaphragm. Not as high fidelity, because the magnet is heavy, but
simpler to build.

http://zone.ni.com/devzone/conceptd.nsf/webmain/4783E9A185B4DDB48625684F006D33C3?OpenDocument

--
John Popelish
 
Take a shoebox lid, affix two razor blades vertically an inch or
so apart, and lay a pencil lead across them. When the box vibrates,
it changes the resistance between the contacts, just like a carbon
mic.

Also, just a piece of foil suspended between the poles of a horseshoe
magnet, with contacts to sense current at right angles to the mag.
field; this is called a "ribbon" mic.

Good Luck!
Rich

Magoo wrote:
I'm looking for some info on building a microphone out of scrap materials
as a science project. I've googled it but didn't find anything really good.

Anyone know of a page that describes how to build microphone from scratch?
Or maybe you have some tips of your own?
Click to expand...
 
Rich Grise <spamdump@nowhere.at.all> wrote in
news:3FCFEA57.64589EE0@nowhere.at.all:

Take a shoebox lid, affix two razor blades vertically an inch or
so apart, and lay a pencil lead across them. When the box vibrates,
it changes the resistance between the contacts, just like a carbon
mic.
Click to expand...
Right. This is what I was looking for. I can't find info on how this
works. I dont mean details on how to do it, I mean explanation of the
principle.

So in your hint above, you run current through the razor blades, and as
the shoe box vibrates, the pencil lead bounces? It's more or less a
mechanical thing and carbon is used only because it's a conductor that
happens to bounce well?

I saw a page that explains how to build a working model of Bell's first
telephone. It had a wire suspended from a diaphram over a copper cup
containing vinegar. As the diaphram vibrated, the wire would contact
the vinegar and current would be passed through the vinegar to the cup.
So that's an entirely mechanical set up.

Also, just a piece of foil suspended between the poles of a horseshoe
magnet, with contacts to sense current at right angles to the mag.
field; this is called a "ribbon" mic.
Click to expand...
If I understand things, this is a little bit different though, right?
This method depends on the small amounts of current generated in the
foil as it moves w/i an magnetic field. Is that right?

Wouldn't you need some way to amplify the signal?


--
Magoo
 
A condenser mic is basically a capacitor right? shouldn't I be able to
build one at home? I have read a few pages on the net talking about buying
a mic and using the capsule -im not too excited about that
someone must have built the first one by hand.
aren't the best capsules built by hand?
 
Patina Creme wrote:
A condenser mic is basically a capacitor right? shouldn't I be able to
build one at home? I have read a few pages on the net talking about buying
a mic and using the capsule -im not too excited about that
someone must have built the first one by hand.
aren't the best capsules built by hand?
Click to expand...
You may well be able to build a decent condenser microphone. It is
basically a capacitor with an air dielectric and one plate is a
diaphragm with a bias voltage applied. In most modern ones, the bias
is replaced with a slab of plastic that has an electric field trapped
inside (called an electret) but you could also make one of those.
Here is a site that hay help you with the basics, and give you the key
words to use in Google to look further.
http://users.telenet.be/educypedia/electronics/microphones.htm
--
John Popelish
 
On Sat, 06 Dec 2003 06:21:34 GMT, Patina Creme
<PatinaCreme@Comcast.net> wrote:

A condenser mic is basically a capacitor right? shouldn't I be able to
build one at home? I have read a few pages on the net talking about buying
a mic and using the capsule -im not too excited about that
someone must have built the first one by hand.
aren't the best capsules built by hand?
Click to expand...
Electret mics are normally used instead of pure condenser mics,
which require 200V bias and are typically >US$1000. The little
electret capsules are only a buck of two and run on a few volts,
having built-in FET preamps.

However, it is possible to build your own electret, though I've never
done it myself. The trick of an electret is a plastic film which
forms the membrane and is permanently polarized with high voltage
(200V, etc), sort of like an electrostatic equivalent of a permanent
magnet. You do this by applying 200V across the film while it is
cooking in an oven at just the right temperature, and cooling it
with the voltage applied. Then when you remove the voltage,
the plastic retains the charge because some polar molecules
have rotated while the plastic was warm and soft, and can't rotate
back when it is cool.




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
 
On Fri, 5 Dec 2003 15:29:52 +0000 (UTC), Magoo
<johnheim@nospam.tds.net> wrote:

Rich Grise <spamdump@nowhere.at.all> wrote in
news:3FCFEA57.64589EE0@nowhere.at.all:

Take a shoebox lid, affix two razor blades vertically an inch or
so apart, and lay a pencil lead across them. When the box vibrates,
it changes the resistance between the contacts, just like a carbon
mic.

Right. This is what I was looking for. I can't find info on how this
works. I dont mean details on how to do it, I mean explanation of the
principle.

So in your hint above, you run current through the razor blades, and as
the shoe box vibrates, the pencil lead bounces? It's more or less a
mechanical thing and carbon is used only because it's a conductor that
happens to bounce well?

I saw a page that explains how to build a working model of Bell's first
telephone. It had a wire suspended from a diaphram over a copper cup
containing vinegar. As the diaphram vibrated, the wire would contact
the vinegar and current would be passed through the vinegar to the cup.
So that's an entirely mechanical set up.

Also, just a piece of foil suspended between the poles of a horseshoe
magnet, with contacts to sense current at right angles to the mag.
field; this is called a "ribbon" mic.

If I understand things, this is a little bit different though, right?
This method depends on the small amounts of current generated in the
foil as it moves w/i an magnetic field. Is that right?

Wouldn't you need some way to amplify the signal?
Click to expand...
For many years the standard microphone in telephony was a
carbon button mic. It was essentially a little chamber of
carbon dust between two conductors. When sound vibrated
the dust, the resistance changed in time with the vibrations.
The big advantage was really high output, since the voltage
across the carbon was fairly high. (I'm not sure if they used
the phone line 48V directly, but something like that.)



Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
 
Patina Creme (PatinaCreme@Comcast.net) writes:
A condenser mic is basically a capacitor right? shouldn't I be able to
build one at home? I have read a few pages on the net talking about buying
a mic and using the capsule -im not too excited about that
someone must have built the first one by hand.
aren't the best capsules built by hand?

There was an article in Popular Electronics around 1968 about electret
Click to expand...
microphones, and there was a section on making your own electret microphone.
Obviously, it was for the sake of understanding it, rather than making
one that one would use for regular activity. The one part I do remember
is their suggestion of using the high voltage out of a tv set to charge
the microphone.

Michael
 
Let's see if I can throw a few ideas your way. Already, two posters have
mentioned the carbon rod on two razor blades and the condenser microphone
methods. Actually, almost any taut foil next to a piece of Mylar with another
foil on its backside would make a pretty decent microphone.
How about using a small light source and reflecting it off a foil element
and catching the resulting reflected beam with a photodiode or phototransistor?
Then you get an optical microphone.
Or, stretch a metal wire through a gap in a magnet- like a horseshoe type.
Fasten a diaphragm to the wire and wrap a pickup coil around the magnet. The
coil output will be the sound signal.
Or, get some flexible circuit board stock, very thin stuff, and etch an
extremely fine and convoluted pathway that covers its surface. Now, connect
that to a Wheatstone bridge and you have a strain gauge that will turn the sound
signal into a varying resistance.
Just a couple of rough ideas.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
 
In a nutshell, yes, yes, yes, and yes. :)
(more below)

Magoo wrote:
Rich Grise <spamdump@nowhere.at.all> wrote in
news:3FCFEA57.64589EE0@nowhere.at.all:

Take a shoebox lid, affix two razor blades vertically an inch or
so apart, and lay a pencil lead across them. When the box vibrates,
it changes the resistance between the contacts, just like a carbon
mic.

Right. This is what I was looking for. I can't find info on how this
works. I dont mean details on how to do it, I mean explanation of the
principle.
Click to expand...
The current path through the razor blade, to the graphite lead, to
the other blade, and out, has a certain resistance. And yes, the
resistance changes as the lead bounces.

So in your hint above, you run current through the razor blades, and as
the shoe box vibrates, the pencil lead bounces? It's more or less a
mechanical thing and carbon is used only because it's a conductor that
happens to bounce well?

It's a "poor" conductor, so it presents some resistance while
Click to expand...
just sitting there. The same with the carbon grains in a Bell
phone - it's used because it's a "poor" conductor, so that
the resistance will decrease when the pressure (sound wave)
increases, pressing them together, and the resistance increases
on the rarefaction wave.

I saw a page that explains how to build a working model of Bell's first
telephone. It had a wire suspended from a diaphram over a copper cup
containing vinegar. As the diaphram vibrated, the wire would contact
the vinegar and current would be passed through the vinegar to the cup.
So that's an entirely mechanical set up.
Click to expand...
Yup.
Also, just a piece of foil suspended between the poles of a horseshoe
magnet, with contacts to sense current at right angles to the mag.
field; this is called a "ribbon" mic.

If I understand things, this is a little bit different though, right?
This method depends on the small amounts of current generated in the
foil as it moves w/i an magnetic field. Is that right?

Wouldn't you need some way to amplify the signal?
Click to expand...
Yes - the carbon mic doesn't necessarily need an amp, because
it's just a variable resistance, and can be just put in series
with the speaker (which is the way old telephones work. after
all); the ribbon mic is a tiny little generator, and that signal
definitely needs to be amlpified.
--
Magoo
Click to expand...
Cheers!
Rich
 
Thanks for all of the input. I am going to build myself some microphones,
from the carbon mic to the ribbon. There wouldn't happen to be a book out
there on someones shelf titled "How to build microphones from A to Z"?

this website is great. Thanks John Popelish.

http://users.telenet.be/educypedia/electronics/microphones.htm




Thanks again everyone for the info,
Patina
 
see news:alt.binaries.schematics.electronic
for my artists' conception of a ribbon mic.

Cheers!
Rich

Patina Creme wrote:
Thanks for all of the input. I am going to build myself some microphones,
from the carbon mic to the ribbon. There wouldn't happen to be a book out
there on someones shelf titled "How to build microphones from A to Z"?

this website is great. Thanks John Popelish.

http://users.telenet.be/educypedia/electronics/microphones.htm

Thanks again everyone for the info,
Patina
Click to expand...
 
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