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…

Derek K. Miller

Microphone

Basics

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

A microphone is a transducer.

What is that??!!!???A transducer converts

one form of energy into another.

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?

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.

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…

Here we have sound waves

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

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

And this is the magnet….

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.

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.

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…

A dynamic microphone… like this SM58…

And, a condenser microphone like this AKG C214

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”.

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…

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.

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).

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?

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.

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.

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.

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.

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.

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.

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.

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.