reqlogonew.gif (7329 bytes)

HOME RECORDING 

MARCH 15, 2001 ISSUE

A Beginners Guide to Microphones

BY KEN LANYON

Seeing as I continually get questions on this subject from our members [at www.recordingwebsite.com ], I thought I would write a quick article explaining the different types of microphones and their uses.  Microphones are one of the most important parts of the recording signal chain, and, when applied properly, can provide as much personality as different types of guitars do.  For this reason, it is important to know the different qualities of various mics because each has their own specifications.  Hopefully, after reading this article, you will be able to analyze your microphones own properties and place them on the instruments that will benefit the best.

There are two main types of microphones, these being dynamics, and condensers. Each are used for different applications, depending on what instruments you are micing up.  Engineers will always have their own personal favorites from each type, as will you with enough experience.  One thing you should understand is that between the two classes, different mics can handle different levels of volume.  These levels are called SPLs, or Sound Pressure Levels. Dynamic microphones and condensers differ greatly in this area, as dynamic microphones can handle higher SPL levels than condensers.  In fact, dynamic mics are specifically reactive to high SPLs, even if there is background noise, whereas condensers can usually differentiate between background and foreground noises.  Having said that, let's dive into the functioning and characteristics of these two microphone types.

Dynamic microphones are a popular choice for live sound applications, but are also used in the studio for those instruments having high attack volumes, such as snare drums. The reason for this is that dynamic microphones can handle higher SPL levels than condenser mics, as I already stated. The way they work is that the sound of the instrument enters the microphone, and immediately hits the diaphragm. This causes the diaphragm to move back in forth with the soundwave. The diaphragm is then connected to a coil that is suspended between two magnets. When the coil is vibrated due to the movement of the diaphragm, an electrical current is induced from the coil moving between the positive and negative fields of the magnets. It is this mic-level signal that travels down the wire to be amplified by the preamp, and then the result is the sound of the instrument.

As you can see, dynamic microphones are pretty simplistic in design, and as a result, are cheaper in relative relation to condenser microphones. You can find Shure SM-57 mics for as low as $80 at some dealers. But even the larger dynamics, like the AKG D112, are usually under $400. Some dynamics come with variable high-pass filters, which I will talk about later in the article, but these are usually the more expensive models. Also because of the design, they are more rugged because of the lack of sensitive parts like condensers have. They are built to be more rugged, so that if they are dropped, the diaphragm and electronics aren't damaged. It has been said that the SM-57, while being a fantastically versatile mic, can also double as a hammer in a pinch!

Condenser microphones are the main type used within recording studios. This is because they usually have better frequency responses, increased sensitivity, and are generally of higher quality. The frequency response of a microphone is the range of frequencies that it can pick up as well as any inherent frequency cuts or boosts due to the electronics. For example, an SM-57 can record frequencies from 40-15,000Hz, while having a +5db boost at 6000Hz. It also rolls off on the low end at 200Hz and rolls off the high end at 14KHz. When buying or choosing a microphone, it is important to look at the frequency response of the mic and compare it to the frequencies put out by the instruments you want to use it on. An AKG D112 mic is great for kick drums because its frequency response is boosted in the low end at around 80-90Hz, but is pretty flat between 400Hz to 2KHz.

Condenser microphones are the main type used within recording studios. This is because they usually have better frequency responses, increased sensitivity, and are generally of higher quality. The frequency response of a microphone is the range of frequencies that it can pick up as well as any inherent frequency cuts or boosts due to the electronics. For example, an SM-57 can record frequencies from 40-15,000Hz, while having a +5db boost at 6000Hz. It also rolls off on the low end at 200Hz and rolls off the high end at 14KHz. When buying or choosing a microphone, it is important to look at the frequency response of the mic and compare it to the frequencies put out by the instruments you want to use it on. An AKG D112 mic is great for kick drums because its frequency response is boosted in the low end at around 80-90Hz, but is pretty flat between 400Hz to 2KHz.

Condensers work by having two opposed plates that are electrically charged (one positive, one negative) by an external power source. This power source is called phantom power, and can come from either the mixing console, or a microphone preamp, traveling down the microphone cable to the mic. Of the two plates, the top one acts as the diaphragm (the bottom one is fixed) and moves along with the sound waves that hit it. Because these plates are charged, the motion of the diaphragm changes the distance between them, and creates an electrical signal of varying energy, which now represents the original audio soundwave.
Unlike dynamics, condenser microphones more often come with extra options to control the sound, such as variable polar patterns, replaceable capsules, pads, high-pass filters, and shock mounts. Pads are helpful to drop the volume electronically by 20db when the sound source you are miking is distorting the preamp due to its inherent volume. High-pass filters are great for getting rid of low frequency noise when miking things like high-hats and cymbals. It can also be used to reduce proximity effect, which is the increase of bass frequencies due to higher SPLs when the mic is moved closer to the sound source. Many of the more expensive condenser models are tube microphones, which definitely add to the warmth of the mic, and these tend to be the most popular vocal mics. However, because of the higher quality and fragility of condenser diaphragms and tubes, they have to be handled with more care.
Condensers cover a wide range of prices, depending on the quality and size of the diaphragm. Larger diaphragms allow for a wider frequency response and have a relatively higher SPL sensitivity, but as a result, cost more. You can get an AKG C1000 small diaphragm condenser for around $200, or a large diaphragm Neumann U87 for $2000. There are even AKG C12s that go for $12,000, so it is possible to spend a small fortune in getting the right sound. Don't let this discourage you though, because there are many condenser mics below the $1000 mark that sound good and are reliable. Two of my favorites are the Neumann TLM 103 and the Audio Technica AT4050.
Ribbon microphones are also a third type of microphone, but can really be classified as a sub-set of dynamics. They work almost the same as dynamic mics except for the fact that they have a ribbon of metal suspended between the two magnets instead of a coil. This ribbon, which is also the diaphragm, is very thin and fragile, and make them as delicate and expensive as some condensers.  Ribbon mics are a little more difficult to find, and while there are a few that are currently in production, it is the older vintage models that are really worth the money. 
One thing I will warn you about is using phantom power with ribbon mics - phantom power is not required for their operation and should be turned off if possible for the channel it feeds.   Phantom powering places 48 Volts on the pins that send the audio signal out of the microphones.   This is applied in such a way that it doesn't interfere with the microphone's operation providing that you use it correctly and you don't have a shorted microphone cord.  One rule is to apply phantom power after the microphones are plugged in.  If your board has one phantom power switch, activate it after the microphones are plugged in and turn it off before unplugging microphones.  Plugging in a mic when the phantom power is active makes a loud pop that can cause damage.  The ribbon microphone is the most fragile microphone and could be damaged by this.  Shorted microphone cords can place 48 volts across the microphone's output and can damage both ribbon and dynamic microphones.  
Having talked about the main types of microphones, I want to move onto the topic of polar patterns. Polar patterns determine where the sound source can be located in relation to the diaphragm so that the sound can be recorded accurately. There are 4 main pattern types, these being Omni, Cardioid, Hemispherical, and Bipolar. Omni patterns will pick up all sounds around the microphone. Any sound source in front, back or to the sides will be picked up equally in volume relative to their distance from the mic. Cardioid patterns pick up sounds mainly in front of the diaphragm but also picks up a little bit to each side. The pattern looks similar to a kidney just off the tip of the mic. A spin-off of the cardioid is the hypercardioid pattern, which is very similar to the standard cardioid, except that it picks up a smaller area on the sides. Hemispherical patterns only pick up an area of 180 degrees around the mic, and thus don't pick up sound from the rear. Bipolar microphones pick up sounds that are to the front and rear of the mic, but tend to shun the sounds coming from the sides. Keep in mind that any mic will pick up a sound if it is loud enough regardless of where it is located, but when it is outside of the polar pattern range, the resulting sound will exhibit what is called off-axis coloration. This is an alteration in the frequency response as the source leaves the range of the polar pattern. This means that the sound is not as accurate, and may tend to sound muddier. All mics come with a polar pattern diagram, which outlines the varying degrees of off-axis coloration.

COMMON PICKUP PATTERNS

All of these patterns are useful to decide what you are recording. Vocalists singing live like to use omni microphones because they tend to move around a lot. The microphone may be directly in front of their mouth one minute, and then be to either side the next, but regardless, their voice is always picked up well. Cardioids are good for miking up background vocalists, where there is a vocalist in front and to both sides. A hypercardioid would be good for this application also, but would be able to deflect other vocalists or instruments further out in the studio. A bipolar mic can be used in stereo miking applications to pick up the side signals while a cardioid picks up the sounds to the front. It is also a good pattern to use when you want to record two instruments or vocalists facing each other. So as you can see, choosing the right polar pattern for your instruments is as important as choosing the right mic for your instruments based on its frequency response.
Finally, I want to wrap up this article by giving you examples of common microphones that I have seen and read about being used on various instruments. Hopefully this will give you an idea of where to start miking your next recordings. Until next time...
Kick Drum AKG D112 (dynamic), AKG D12 (dynamic), Sennheiser MD421 (dynamic),
Snare Drum (top and bottom)

 Shure SM-57 (dynamic), Sennheiser MD421(dynamic), AKG 414 (condenser)

High Hat

Shure SM-57, Shure SM-81, Neumann KM-184

Toms

Sennheiser 609s (dynamic), MD421, SM-57

Overheads (cymbals) Shure KSM-32 (condenser), Shure KSM-44 (condenser), Neumann TLM 103 (condenser), Neumann U87 (condenser), Neumann U89, KM-184 (condenser), AKG 414
Room Mics

AKG-414, AT-4050, AT-4033, U-87, U-89, TLM-103, KM-184,

Guitars

SM-57, MD421, AKG 414, Sennheiser MD441 (dynamic)

Bass

AKG D112, AKG D12, Shure Beta 52 (dynamic), MD421,

Vocals

AKG-C1000, AKG-C3000, AKG-414, AT-4050, AT-4033, U-87, TLM-103, Rode N1, Rode N2,

Piano

U-87, TLM-103, KSM-32/44, AKG-414

Acoustic Guitar

AKG-C1000, AKG-C3000, AKG-414, AT-4050, AT-4033, U-87, TLM-103,

Copyright 2001, by Ken Lanyon, ALL RIGHTS RESERVED

Illustrations Copyright 2001, by Robert Dennis, ALL RIGHTS RESERVED

Published in Recording Engineer's Quarterly and Alexander magazines with permission

USE OF THIS ARTICLE SUBJECT TO USER AGREEMENT

RETURN TO MARCH, 2001 ARTICLE INDEX

RETURN TO REQ HOME PAGE