Microphone Basics: Type, Frequency Response, and Polar Pattern

Hello everyone,

My name is Gary Furlong.  I am originally from Ireland but I am currently living in Japan in a city called Itoigawa.  I will be covering the topic of Microphone basics.  I will attempt to tell you all what I know through the medium of my blog (which has not been updated in about a year…oh dear).   I hope you find yourself educated and entertained.  I chose this topic as it is one in which I feel I lack a lot of understanding, so it is about time I learned.

This is me by the way, I’m being bitten by a good luck Dragon:

Om nom nom nom Gaijin head!!!

Om nom nom nom Gaijin head!!

So let’s get started.

I would like to do a broad overview on each topic mentioned in the title of this lesson.  They are as follows:

  • Type
  • Frequency response
  • Polar pattern

Music class Let's go

Type

In this section I will focus on the two main types of microphone: Condenser and Dynamic.  I will give a brief overview of each type and suggest some uses for each.  Let us assume that the Dynamic mic is cardioid and the condenser is an omni-directional microphone.  These are common types of each mic and we will go into more detail, explaining the terms cardiode and omni-directional in later sections.

Condenser Mics.

The first thing to note about condenser microphones (sometimes called capacitor microphones) is that they are very sensitive in both build and in how they pick up sound.  This makes them (generally) unsuitable for use on stage, especially for vocals.

The singer will need to hear themselves and will use onstage monitors to do so.  The high sensitivity of the mic means that not only will it pick up the singers voice as it comes from the singer’s mouth, it will also pick up what is coming from the monitor.  This will result in feedback.  See Fig 1

For recording drums or for overhead use in recording choirs in an acoustically treated room for example the extra sensitivity of the condenser mic proves very effective as it produces a very natural sounding recording.

Condenser mics have an on board premap that will need to be powered to function.  This is called Phantom power and it will usually come from whatever external mic pre-amp you are using but external power sources can also be used.  This is another reason why they are not suitable for live performances.

Fig1.

Music class condenser

Condenser mics are recommended for use in the studio.  They preform very well over a wide range of frequencies (which we will discuss in a later section).  In home recording (in a room that has not been treated for sound recording) as most condenser mics are omni-directional, they will pick up noise such as computer fans and hard drive operation noises, any minor movement the singer/player makes such as chair creaking etc.

Suggested uses: recording drums, piano and other instruments that can give out high end frequencies and studio vocals.

Dynamic Microphones.

Dynamic mics are more rugged than condenser mics.  They are also less sensitive.  For this reason they are perfect for stage vocals.  As we see in Fig 2. any extra noise on the stage is not picked up by the dynamic mic and so only the singer’s voice comes from the speaker.

Fig 2.

Music class Dynamic fuck

Dynamic mics do not require phantom power so they are pretty much plug in and play.  However, as mentioned before they are less sensitive and so will not pick up certain frequencies (roughly above 16kHz and below 100Hz ).       The robust build of the dynamic mic allows it to take much more abuse than the condenser.  This makes it the ideal stage mic as some performers are often wont to swing mics, pick up the mic stand and toss it around etc.

In my experience there are certain areas when dynamic mics are preferable to condenser mics for vocal recording.  I am a member of a charity organisation which performs a charity musical every year.  We have 8 weeks to complete rehearsals and begin performances.  To back up the singers I record vocals and add them to karaoke tracks.  Given that we have an extremely short time frame I often find I have to record in less than ideal situations.  Singing, acting, dancing rehearsal and vocal recording all take place at the same time.  I take whoever I am recording to the quietest area I can find and record vocals.  I have found the lower sensitivity of the dynamic mic to really be an advantage.  The singer’s close proximity to the mic makes their voice the dominant sound essentially drowning out any unwanted noise.

Suggested uses: Stage vocals, recording electric guitar from amp, vocal recording in less than ideal conditions.

This has been a very basic introduction to microphone type.  There are other factors to consider and I will discuss them in the next two sections.

Frequency Response

“Frequency response refers to the way a microphone responds to different frequencies.”

Frequency response is a very important factor to consider when purchasing a microphone.   Both condenser and dynamic mics have very different frequency responses.  For example if you wish to record just a vocal you will need a mic that will respond well to the frequency of the human voice and attenuate (reduce) other undesirable sounds.  I mentioned above that I chose a dynamic mic for recording vocals in bad conditions.  This was due to its frequency response (even if I didn’t know it at the time), it exaggerated the performance of the singer while attenuating most of the room noise.  In the past I only had a condenser mic which would take in almost every sound in the room.  This meant I had to very politely ask a large group of twenty something year olds to be quite or go away.

One thing I noticed when using both mics was the sound heard when putting on your headphones to begin recording.  With the dynamic mic there was no noticeable background noise however, with the condenser mic I realised just how noisy the room was.  I heard clocks ticking, the computer running, any slight movement of my chair, the room almost sounded crowded.

If you look to Fig 3 you will see a typical Frequency Responce chart.  This shows the frequencies at which the mic responds well and those frequencies that will be attenuated.

Fig 3.

This is the frequency response chart for the Shure SM27.  It is a large diaphragm condenser mic.  We can tell this mic is designed to take in as much sound as possible.  The X axis shows the frequencies at which this mic will function well.  We can see there is very little attenuation, the only really noticeable point is at around 19kHz where it drops slightly.  Otherwise this mic will perform well at all frequencies from 20 – 20kHz.

Polar Pattern

In Fig 1 and 2 above you will notice in the diagram there is a section marked “Zone of sensitivity”, this can be more accurately labeled as “Polar Pattern”.  Polar Pattern refers to what areas around the microphone are picked up well and what areas are rejected.

In this section I will give a brief overview of the three main types of polar patterns:

  • Omni
  • Figure of eight
  • Cardioid

Omni directional

The first pattern I will talk about is Omni-directional.  This means that the microphone will pick up sound from all directions.  These are often referred to as “pressure mics” as they only measure sound pressure in space (vocals, instruments etc) and not the direction from which it comes.  They provide a very natural sound.  Because of this the room in which you record is very important.  If the acoustics of the room are too sharp and reflective or if they dampen the sound the recording will show it.  Fig 4 shows an omni directional polar pattern.

Fig 4

Figure of eight

Figure of eight microphones record are sensitive to the areas in the front and back of the microphone.  These respond to pressure gradients in these areas and are sometimes called “Velocity mics” due to the way the mic detects the velocity of sound waves.  Fig 5 shows the polar pattern of a figure of eight microphone.

Fig 5

Cardioid

This is the final polar pattern I will talk about.  This pattern is mostly used in directional condenser and dynamic microphones.  It is a popular choice for use on stage as it rejects sound from the back of the mic and focuses mainly on the front where the singer will be screaming into it.  There are variations of the Cardioid pattern such as:

Hypercardioid: Detects a small amount from the back of the mic

Hypocardioid:  Detects a slightly more focused area in front of the mic

Fig 6 shows the cardioid polar pattern.

One interesting fact I discovered while researching this topic was that the two fundamental polar patterns from which all others are derived are Omni and Figure of eight which I discussed above.  The other patterns including cardioid are formed by combining and manipulating varying degrees of the omni and figure of eight patterns.  It is also important to note that polar patterns are 3D as shown by Fig 7.

Fig 6.

Fig 7

 

I hope this post has been enjoyable to read.  Any criticism is welcome, I know it is far from perfect but this experience alone has really helped with my understanding of Microphones (I just discovered the condenser mic I have owned for the past 3 years is cardioid) and I hope it has helped any other beginners out there with questions about microphones.  I look forward to talking to you all soon.

Gary.

Sources:

http://www.soundonsound.com/sos/Jul03/articles/firstmic.asp

http://www.soundonsound.com/sos/mar04/articles/computervocals.htm

http://www.mediacollege.com/audio/microphones/frequency-response.html

https://class.coursera.org/musicproduction-001/lecture/index

http://www.soundonsound.com/sos/mar07/articles/micpatterns.htm

About gazztastic

This blog is another attempt at self motivation to do these four things in a year: (In order of supposed difficulty) 1). Achieve at a 75% or higher in the JLTP 二級 test. 2). Write and record a song every two months 3). Learn all the modes in guitar, learn to play at least 3 classical pieces and learn to sweep pick. 4).......lose 10 kilos Should be doable if I can make myself get up and do them!!!!
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3 Responses to Microphone Basics: Type, Frequency Response, and Polar Pattern

  1. baz says:

    Cool post Gar! Here’s a cool rambly video on geometry, parabolas and cardioids (aka anti-parabolas): https://www.youtube.com/watch?v=v-pyuaThp-c

  2. Johnb458 says:

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