This document provides an overview of microphones and how they work. It discusses that a microphone is a transducer that converts sound waves into an electrical audio signal. It does this through a diaphragm that vibrates from sound waves, moving a coil of wire over a magnet to create a current. There are different types of microphones like dynamic and condenser microphones that are suited for different purposes, with dynamics commonly used for vocals and condensers for studio recording due to their sensitivity. Key specifications like frequency response and polar pattern are discussed to understand what sounds microphones will pick up and from what directions.

1. Hi. My name is Jan Zurcher.
I’m a singer-songwriter living in a
small town called Friday Harbor, San
Juan Island, Washington
This lesson is for Week 1 of the
Introduction to Music Production
Course at Coursera.org. The topic I
have chosen to look at is…

2. Derek K. Miller

3. What exactly is a
microphone? I mean,
I’ve seen one and all
but…
A microphone is
a transducer.

4. What is that??!!!???
A transducer converts
one form of energy
into another.

5. In the case of a microphone, it
converts acoustic energy (sound
waves) into electrical energy.
That’s called an “audio signal”.
How does it do that?

6. Well… sound creates vibrations (or waves) in the air.
A microphone usually has a small thin piece of
metal in it – called a diaphragm.
When the sound wave hits the diaphragm, the
diaphragm picks up the wave action and starts
moving in and out at the same rate as the sound
wave.

7. Attached to the diaphragm is a coil of wire
wrapped around a magnet.
As the diaphragm moves in and out, it
pushes the coil back and forth over the
magnet and an electrical current is created
– that becomes the audio signal
???
Maybe a picture would help…

8. Here we have sound waves

9. This is a very thin piece of metal – that’s the diaphragm…

10. The sound waves move the diaphragm back and forth… which
moves the coil of wire back and forth. This is the coil…

11. And this is the magnet….

12. That motion of the coil of wire across the magnet creates an
electrical current…. these are the wires that carry the
electrical audio signal along the microphone cable.

13. But aren’t there all
kinds of different
microphones?
Yes, there are –
dynamic microphones,
condenser microphones,
ribbon microphones,
crystal microphones…
But, for most of
them, the basic
principles of how
they work are the
same.

14. So, then… Why are there so many
different kinds of microphones?
Wouldn’t there be one best one that
everyone would use?
That’s a good question. But, no.
Different situations call for different
kinds of microphones that are designed
to handle that need…
However, in reality, there are two types
of microphones that are most
commonly used…

15. A dynamic microphone… like this SM58…

16. And, a condenser microphone like this AKG C214

17. Dynamic microphones are the
ones that you often see being
used by singers on a stage…
They are designed to pick up
sounds from certain directions
so that they don’t pick up a lot
of other sounds from the stage
– particularly the monitors in
front of the singer… if they do
that you get that squealing
sound known as “feedback”.

18. Condenser microphones are
used in many different
situations but are generally the
preferred type of microphone
for use in the studio…
This is because they are
designed to be very sensitive
and pick up sounds very
accurately…

19. So, if I wanted to buy a
microphone, what
should I look for?
Well, you would want
to think about what
you were going to do
with it and then look
at its frequency
response and its polar
pattern.

20. What’s frequency response?
It’s a way of describing what frequencies a microphone is designed to
pick up the best. But, let’s go back one step…
Frequency is a word used to describe how “fast” a sound wave is
vibrating. Frequency is measured in Hertz.
One hertz is one pulse per second. That’s pretty slow and people
can’t hear sounds at that frequency.
In theory, the slowest (or lowest) frequency sound that people can
hear is 20 hertz and the highest is 20,000 hertz (or 20 kilohertz).

21. A dynamic microphone – like the SM58 is
designed to respond really well to the
frequencies within the vocal range and not to
respond as well to other frequencies.
The typical range for human singing voices from
bass through soprano is approximately between
80 Hertz and 1050 Hertz.
So you want your vocal microphone to be really
good at picking up those ranges as well as their
overtones or partial frequencies.
So, how do I tell what
frequencies a microphone is
designed to pick up the best?

22. You look at their “frequency response” chart –
like this one for the Shure SM58. This is a
microphone designed for a vocalist to use on
stage.
Notice that the the frequency response starts
around 90 Hertz and drops off significantly at
about 10,000 hertz.

23. Compare that to this frequency response chart from an
AKG C214 large diaphragm condenser microphone.
For this microphone, the microphone response begins at
about 30 Hertz and remains fairly flat until it peaks at
about 12,000 Hertz and is still responding at 20,000 Hertz.
That’s pretty much the entire spectrum that people can
hear.

24. So, given that the condenser
mic picks up the range that a
dynamic mic does and more,
why wouldn’t I just use a
condenser mic for everything? Because a dynamic mic is
directional. It gives a pretty focused
sound and lets you isolate the
sound that is right in front of the
mic because the mic is pointed right
at the source of that sound.

25. Does that have something to do
with that that other thing you
said I should look for when
buying a mic?
What was that again?
The “polar pattern”.
That’s a diagram that
describes the area
around the mic that is
picked up well.

26. Here’s the polar pattern for the Shure SM58 – remember, it’s a dynamic
microphone. This type of pattern is very directional – that is, it is
designed to pick up sounds directly in front of it… from a more or less
single direction.
You can see that the pattern is shaped like a heart… that’s why it is
called a cardioid pattern. This diagram also shows that different
frequencies have a slightly different shape.

27. In contrast, here is the “polar pattern”
for an AKG C214 large diaphragm
condenser microphone.
Notice that this pattern shows that
sound is being picked up quite well from
all directions.

28. Remember, though, some condenser
microphones can be very directional –
just like the SM58 is.
Others come with switches that let you
chose the polar pattern. This gives you
more flexibility in terms of how you use
the mic.
Also notice that, just as with the
dynamic microphone, different
frequencies on this mic, have slightly
different polar patterns.

29. Whew! Thanks, Zak.
That’ a lot of things to think about
but I think I understand a little bit
more about microphones and how
they work.