Last updated: 1/28/99

There are several basic types of microphones:

• Dynamic Mics (moving coil mics)
• Ribbon Mics (pressure gradient mics)
• Condenser or Capacitor Mics
• Printed Ribbon or Regulated Phase Mics
• Ceramic
• Crystal (these last two, you don't need to worry much about)
  

We'll discuss each one of these in detail.

• Dynamic Mics

These are sometimes called moving coil or pressure mics.

How they work:

• Sound hits a moving diaphragm attached to a moving coil between magnetic fields.
• Vibration produces electrical wave which carries the imprint of the sound.
• Small, inexpensive, excellent frequence response (highs and lows).
• These mics are sturdy but heavy.
• They are fairly insensitive to wind, but very good with loud sounds..
• They may also exaggerate plosives in some people.
• These mics are not grat with higher frequencies and softer sounds.

The size the diaphragm in a microphone determines the range of frequencies the mic can pick up. The same thing is true of the diaphragm in the human ear - the ear drum. The shortest wavelength that a young human ear can hear defines the size of the diaphragm in a quality pressure mic.

• Ribbon Mics.

These are also sometimes called pressure gradient mics because of the way they are constructed.

How they work:

• A light, delicate ribbon is placed between poles of a magnet.
• That ribbon is a magnetic conductor.
• Sound waves vibrate against the ribbon.
• Electrical waves are formed by the difference in pressure between the front and the back of the ribbon (thus the "pressure gradient" label).
• This mic was very widely used in the 30's and 40's.
• It is less widely used now.
• They make your voice sound very good. (That's why they were used by Johnny Carson, and one still sits on David Letterman's desk.)
• However, these mics are very heavy and very fragile. They are usually used only in studios.
• They are so fragile that a very loud sound can snap the ribbon!

Condenso Mics:

How they work:

• These mics use an electrical element called a CAPACITOR which is an electrical device with a diaphragm and a backplate.
• The capacitor is actually a storage place for the electrons which produce the signal.
• There is a dead air space between those backplate and the diaphragm.
• The alteration of that dead air space due to pressure produces the electromagnetic signal. (The system works much like a whoopie cushion.)
• These mics are the most compliant (sensitive).
• They are small and light.
• They are cheap and rugged.

Early condensor mics had a weak signal and they were expensive because they required so much energy. They had to have an auxiliary power supply and an internal amplifier. Now they have an internal power supply.

These are the microphones that are built into tape recorders. They do not work as well with mic cords, because of their need for power. They are high impedance mics. (We'll discuss impedance in a bit.)

• Regulated Phase Mics or Printed Ribbon Mics.

These are a combination of a ribbon mic and dynamic mic. They have the durability of dynamic mics and the compliance of the ribbon mic.

• Crystal and Ceramic mics are not something you have to worry about. They are very old mics and not used much any more.
• Digital Mics
  

These are fairly new on the market and not a lot of information is available about them. What few are out there are REALLY expensive ($3000.00). None of the current mics are recommended for radio broadcasting.

You should know that there may be some problems with mic cables. You will need a digital cable. You can use it for an analog mic, but you may not be able to use your analog cables with a digital mic.

For an excellent web site concerning microphone cables, check out the RADIO WORLD site at http:www.rwonline.com/readingroom/rr-wired_for_spound8.html

As a rule, broadcasters don't usually run out an buy the first brand-new thing out there. They like to stick with proven technology because it doesn't "go south" at a crucial moment. So the top four mics we've mentioned will be around for a while. Digital mics will happen, but it may take a while for wide adoption.

Basic Microphone Characteristics:

All mics have certain characteristics

• frequency response
• polar pattern
• compliance

Range: This refers to the range of highs and lows or the amount of the spectrum the microphone can hear. Good microphones hear all sound equally well at + - 5 dB.

Shape: This refers to the mic frequency response pattern. It is shown on a graph. The graph shows which frequency the mic picks up well and which one it doesn't. Some mics have a "boost" in those frequencies which make the voice sound better.

Some information you need related to frequency response:

Accoustic Phase Cancellation: Equal pressure keeps the diaphragm from moving. (Recall the animation in the video we saw in class.) If the diaphragm is is too large, more than one phase hits it at a time and they cancel each other out and the diaphragm can not move. (Remember one phase will strike one side and the next will strike the other side.)

Because if this, certain diaphragm sizes are better for certain frequencies than others. Remember that wave sizes vary with frequency; the higher the frequency, the smaller the wave size.

• Large diaphragms are better because it catches all of the phase. (You have as many problems if you don't get all of one phase on a diaphragm as you do if you get too much; you must have at least one half of a phase if you want a good response to that sound.)
• Small diaphragms are better for high frequencies because you don't get more than one phase and they don't cancel each other out. But small diaphragms have uneven low-frequency response becaus not enough of the sound wave hits the diaphragm to make a difference.

Polar Patterns or Pick-Up Patterns:

Remember: Polar patterns are THREE-dimensional. They have vertical and horizontal characteristics.

Omni-directional:

• Sometimes called non-directional, pick up sound all the way around a mic.
• The pattern is spherical.
• Usually used in dynamic mics
  

Bi-Directional:

• These have a figure-eight pattern (like two spheres touching at the mic)
• Employed by ribbon microphones
• On the beam in these mics is directly perpendicular to the ribbon in the mic.
  

Cardiod:

• Heart-shaped pattern, similar to an upside-down apple.
• Usually found in dynamic mics
• Remember these mics have ports or holes in the back of the base of the mic. The ports are there to shape the pick-up pattern. They allow phase cancellation for ambient sound at the back of the mic. The ports cancel out sound coming from an unwanted direction. Many times performers or technicians will cover the ports with hands or with tape, and destroy the sound quality of the mic by accident.

A microphone's unidrectionality is facilitated by the ports at the rear and side of a microphone.

• Ports closer to the diaphragm process higher frequencies.
• Ports further from the diaphragm process lower frequencies.
• Some mics are identified by the number and type of ports they have:
• Single D's : A mic having one port
• Dual Entry: A mic having two ports
• Variable D: A mic having multiple adjustable ports

Uni-directional:

• These microphones have sensitivity in a very restricted area, on only one side of the mic.
• Supercardioid
• Hypercardioid
• These microphones have very narrow pick-up patterns and are used for exterior sound gathering for news and film production. They can pick up a speaker and not get the ambient sound of the people or environment around the speaker.
  

Multi-directional:

• These mics can be adjusted to more than one polar pattern.
• System mics: use interchangeable heads or capsules which each have a unique pick-up pattern.
• Stereophonic mics: These mics have two distinct elements. The upper one rotates 180 to 360 degrees and thus allows several different pick-up patterns.
• Middle-side or M-S mic: This one has two capsules in a single casing. The first is designated as a middle position microphone and has a bi-directional pattern. The other capsule rotates to 90 degrees from the middle for the purpose of picking up ambient sound.
• Sound field mic-system: Here 4 capacitor mics are mounted on a single casing and they can be rotated to pick up sound from up to four directions. This gives the main signal plus ambient sound from three directions.
  

The polar response pattern is a graph of the mic's directional sensitivity.

Compliance of the Microphone: Compliance refers to the weight or mass of a diaphragm. Like any other surface, heavier diaphragms don't move as easily or as precisely as lighter ones. Think of it as the difference between a sheet of paper and a small piece of plywood. One is much more flexible and fluid than the other. The lighter one is more compliant and does better with higher frequencies.

Terms which are related to compliance:

Transient Response: refers to the quickness with which a diaphragm (or microphone) responds to sound. This is sometimes called the "attack" of the mic. The quickness of the attack is proportionate to the lightness/compliance of the mic. The more compliant the mic is, the better its' attack or transient response.

Impedance: refers to the resistance of flow of an audio signal in a microphone cable.

• Studio mics usually have low impedance or low resistance or "low Z". That means you can use a long mic chord and have little hum, less static, less electrical interference. Chords of up to 1,000 ft. or more are okay.
• High impedance mics have lots of resistance and are sometime said to be "high Z." They have a strong signal, but one which deteriorates rapidly. They must have short cables (less than 20 feet) and are usually non-professional mics.
  

Other microphone-related terms:

Overload: too loud, over-modulating. A level which is too high and causing audio distortion.

Pop-filter: sometimes called windscreens. These foam socks fit over a microphone and absorb the sounds of air moving across the mic so that it is not picked up and does not create a static-like sound. These are mainly used on moving coil and printed ribbon mics and some capacitor mics, mostly of a directional nature. They do not work well on ribbon microphones because they distort the sound.

Using a microphone....some basics:

So how do you "work" a mic to get the best results? It may vary depending on the type of microphone you use. Of course, you have to be in the pick-up pattern, and here are some distance guidelines:

• For the purpose of THIS CLASS work the mics 10- 12 inches.
• Ribbon microphones need to be worked 12 to 14 inches because of their sensitivity to plosives.
• When mics have pop filters, sometimes you can work them as close as 6 to 8 inches, but I advise against it.

If you have a plosive problem,

• use a pop-filter
• talk "across" a mic rather than directly into in (but maintain appropriate distance)
• move back from mic somewhat
  

The "eleventh commandment" for broadcasters: (definitely NOT as important as the first ten, but important to YOU) You shall NOT blow or tap into your microphone!

• Blowing into a mic can damage the delicate internal parts and break the mic.
• Your breath contains all kinds of things that are just nasty! - Germs! Humidity! Tiny food particles! The same stuff that gives you "morning breath" and makes you run for the toothbrush and mouthwash. Do you really want someone to blow into a mic and then YOU inhale deeply as you use it? (I don't think so...) That same nasty stuff will "glom onto" the sensitive parts of the mic and "yuck it up," eventually compromising its effectiveness or making it unusable. While this is not a very academic or technical explanation, you get the point. DON'T DO IT!
• IT MAKES YOU LOOK IGNORANT and UNPROFESSIONAL! If you blow into or tap on a microphone, you might as well hang a sign around your neck that says, "I don't know what I'm doing!"
  

Microphone Positions: These terms refer to where you place YOURSELF in relation to your microphone and with what effect. Do NOT confuse these with pick-up or polar patterns! Every semester a number of students get these confused on the radio exam, so don't YOU be one of them.

On Mic: The announcer is directly in the pick-up pattern and the voice sounds clear and full.

Off Mic: The announcer is outside the pick-up pattern of the mic, and the voice will sound hollow and distant.

Fade On: The announcer moves from an off-mic position to an on-mic position.

Fade Off: The announcer moves from an ON-mic position to an OFF-mic position.

Behind Obstruction: Some sort of obstruction (a notebook, etc) is placed between the microphone and the speaker or sound effect, so it sounds not only distant, but in the next room or behind a door or wall.

Some general rules of "micing":

• Get your microphone as close to the source as possible. Even directional microphones pick up a little sound from most directions, so the closer the better - as long as you're not getting negative effects (plosives, mouth noises, etc)
• Eliminate the Competition: Think about the OTHER sounds in the room where you are recording. Two main sources of unwanted sound are:
• noise : this can be the noisy air conditioner, traffic outside, crowds in the hall.
• ambience : may be the "live nature" of the room you're in, the unwanted echo.
• Do what you can to eliminate the problem and place your mic as close to your subject as possible.

Physical Types of Microphones:

Check your text book for illustrations and further descriptions of these microphone types. Here I will just indicate the obvious ones, and offer some details about some of the others.

Be sure you know each of them...

Handheld mics

Studio mounted mics

Headset microphones:

• These are usually moving-coil microphones with a built-in pop-filter.
• Headsets have phones on one ear which provides the program feed and on the other ear the announcer hears the director's cues.
• Benefits: it frees the announcer's hands and keeps the the announcer's distance from the mic constant.

Lavalier or lapel mics:

• The lavalier mic has a string which hangs the mic around the announcer's neck; these aren't used that much anymore.
• Lapel mics have a clip or a pin. You run the cord under your coat or sweater and attach it above the breast bone, making sure that you will be on mic. That means make sure it's not tilted away from your mouth or in a direction opposite from that in which you will be speaking. Also be sure that the mic is not tilted toward another person on your set, or they could be in your pick-up pattern and then they would sound hollow on their own mic.
• These mics are usually omni-directional because the speaker is talking across the mic rather than into it. In fact, if you speak directly into it, your voice will sound tinny or hissy. You can get them in directional versions, but the omni-directional version is more common.

Shot gun microphones: These are used in the field to get sound bites or sound effects.

• These don't pick up ambient sound because of their high directionality.
• The mic to source distance is MUCH greater and that distance doesn't have an effect on sound quality. (Distance can be 20 times greater)

These mics use a "interference tube" which may be anywhere from 6" to 3 feet in length. The length of the tube affects the mic's ability to deal with wavelengths longer than the length of the tube. Thus they are less effective at lower frequencies.

Parabolic microphones: These look like big dishes, and in reality that's what they are, but they have a microphone in the bottom of the dish.

• They concentrate the sound at the base where the mic is.
• They are most effective in mid and high frequencies.
• Used on the field in sporting events.
  

Wireless mics: These are also called radio mics, FM mics, transmitter mics, cordless mics. They have four components:

• The mic
• transmitter
• antenna
• receiver

The mics (1) send a signal to the battery-powered transmitter (2) which relays the signal to a receiver (3)(4) which may be anywhere from several feet to several yards away, depending onpower. They operate in both the UHF and VHF band and can be mounted on cameras and booms.

Contact mics: these pick up vibrations passing through solid objects

Boundary mics: these are placed near a wall or floor or other reflective surface to shorten the reverb route of the sound in the room. It causes an unnatural or hollow sound as a result of phase shifts in the mic.

Be sure you know the following terms:

mic cables:

• balanced: two conduits and a shield
• unbalanced: one conduit and a conducting shield

mobile mounts:

• boom
• parambulator boom
• tripod or giraffe mobil boom
• fishpole boom

Links:

Check out the reading room at Radio World Online: http://www.rwonline.com Go to the reading room for lots of cool information about microphones, cables, etc.

Another place to check on a regular basis is Vidographer magazine. Each month they have excellent articles about audio and video production. The articles are very basic and very helpful. Find them at http://www.videographer.com .

Sources:

• Adams, Michael and Kimberly Massey. Introduction to Radio - Production and Programming. New York: McGraw Hill, 1995.
• Alten, Stanley. Audio in Media, 4th ed. Belmont, CA: Wadsworth, 1994.
• Burrows, Thomas, Lynn Gross and Donald Wood. Video Production: Disciplines and Techniques, 7th ed.
• Boston: McGraw Hill, 1998.
• Nisbett, Alec. The Use of Microphones, 3rd ed. Boston: Focal Press, 1989.