Mic Types

Has the selection of microphones offered by your favorite electronics store ever overwhelmed you? Have you stared in awe at the vast array of silver or black, big or small, expensive or cheap micro­phones available to you?

Have you won­dered about HiZ versus LowZ, dynamic versus condenser, cardioid versus omni­directional or shotguns and lavaliers versus handheld and boundary mics? Throughout this article, we will take a look at impedance, the two major ways microphones work, microphone pickup patterns and microphone styles. So sit back, relax and proceed through this quick look into the sometimes confusing world of microphone choice.

HiZ and LowZ

Before you choose the style of micro­phone you'd like to use, you have to know what impedance of microphone is com­patible with your camcorder. Your system might require a HiZ microphone input. Impedance is the resistance to the flow of electrical current in a circuit or element.  We measure impedance in ohms, a unit of resistance to current flow.  The lower the impedance, the better the microphone or recording device.

Most older consumer camcorders have a high impedance (HiZ) microphone jack meant to be used with high impedance microphones.  These microphones range in impedance from 600 – 1400 ohms.  HiZ microphones are very sensitive and require very little amplification, which is why less sophisticated consumer equipment is designed for them.  They are, however, susceptible to hum and electronic noise and can be used only with a very short microphone cable.

Low impedance microphones, with an impedance level or 100 – 600 ohms, have become the norm in video production.  Even much of today’s consumer equipment now has low impedance inputs to allow you to use professional microphones.  Using these professional microphones with low impedance gives you two advantages: (1) they are not as affected by electronic hums and noises that can be caused by fluorescent lighting or electric motors and (2) you can use long cables without worrying about outside interference.

If you buy a microphone and plug its cable into your camcorder and nothing happens, it may be due to an impedance mismatch. If your camcorder requires a HiZ microphone and all you have are professional mics, don't despair. You can purchase an inexpensive LowZ to HiZ transformer. Plug your microphone cable into the transformer and the transformer into your camcorder. You should now be able to use any professional microphone with your system. Now that we've gotten impedance choice out of the way, we can move on to the other mic variables.

Inner Workings

Most microphones fall within one of the two major families: dynamic or capacitor (con­denser) microphones. The dynamic micro­phone has a fixedMT01 magnet, a diaphragm that moves when sound hits it, and a coil attached to the diaphragm. When the dia­phragm moves, the coil moves, making changes in the magnetic field. These changes generate voltage through the microphone cable to the recorder, amplifier or speakers (see right).

The dynamic microphone has a number of attributes that you need to take into account when deciding on the type of microphone you need. This type of micro­phone is extremely durable. Dynamic mics can tolerate wide temperature ranges and humidity as well as take a great deal of abuse. I have seen them dropped, banged around, used in the dead of winter, in the high heat of a tropical rain forest and even (believe it or not) used as a hammer (not recommended), all without affecting the mic's ability to record high quality audio. Dynamic mics are also fairly inexpensive. Good quality dynamic microphones like the Shure SM58 costs around $200. Lower quality dynamics run as low as $77. Even the extremely good dynamics rarely cost more than $350.

Another attribute of the dynamic mic is its ability to provide a warm, rounded sound for vocals and yet take the abuse of recording high impact sounds such as drums and screaming voices. Many lead singers in rock bands use the handheld dynamic because of its ruggedness and its ability to pick up a wide range of sounds from screams to whispers. However, the dynamic microphone has a less accurate sound reproduction than the condenser.

A final advantage of the dynamic is that it requires no outside power. Plug it into your recorder or sound system and go. No batteries or power supplies needed. In video work, the dynamic microphone is ideal for on-camera interviews, record­ing very loud sound sources and crawling around the toughest terrain.

MT02The capacitor or condenser micro­phone uses variations in voltage within a capacitor. The capacitor, which is capable of holding an electrical charge, is made up of two parallel plates, one fixed and one moving, separated by a small space. When sound waves hit the movable plate, it vibrates and causes a change in the amount of voltage held by the capacitor. This change in voltage is sent down the wires to be recorded or amplified through speakers (see left).

The condenser microphone has a number of attributes that are important for the videographer to consider. The condenser mic is not so rugged as the dynamic, and the more expensive models are downright delicate. They range in price from around $100 for a basic condenser to well over $5,000 for a high-end studio mic. Although the condenser is usually more expensive, its frequency response and true sound ren­dering make it ideal for the videographer seeking the best fidelity.

You will have to consider one other attribute when purchasing a condenser microphone: its need for an additional power source. A battery, or AC power source can provide this additional "phan­tom" power. If you have a mixing board with phantom power built into the inputs, it will supply power to any mic you plug in. You can purchase a condenser microphone and begin using it right away. However, if you plan to plug a phantom-powered microphone into your camcorder, you'll need to purchase a phantom power unit to supply juice for your mic. Fortunately, most microphones that you would use for field production have a battery space built in. You just have to remember the batteries.

Pickup Patterns

Whether you choose either a dynamic or condenser microphone, you must also decide the best pickup pattern for your production. There areMT03 four primary pickup patterns to choose from: omnidirectional, cardioid (or unidirectional), hypercardioid (or shotgun) and bidirectional (see left).

The omnidirectional microphone picks up soundin every direction-front, backand sides (see a). This microphone is good if the sound source comes from a wide variety of directions and is moving from one side to another in front of the mic.

The cardioid or unidirectional micro­phone picks up sound primarily in a heart shape from the front of the microphone, including a little from the sides, but does not pick up from the back (see b). This pickup pattern is excellent for voice mics and miking musical instruments.

The hypercardioid microphone picks up only sound from the front and is very direc­tional (see c). You must point it at the sound source to get a good pickup. This type of pick-up pattern is excellent for isolating sound sources like bird calls, individual actors talking in a drama, or isolating one voice in a sea of voices.

The bidirectional microphone picks up sound from two distinct sides of the mic (d). You would use a mic with this pickup pattern primarily to record two voices talking into the same microphone.

You can find all ofthese pickup patterns in a variety of microphone styles. Some of the more expensive microphones even have switches that enable you to choose multiple patterns from a single mic.

Styles of Microphones

MT04After you make the choice between dynamic and condenser, and select an appropriate pickup pattern, you have to choose what style of microphone to use. This choice is entirely dependent on the type of produc­tion you are doing and whether or not you want to see the mic on screen. The major types of microphone styles are: handheld, shotgun, lavalier or lapel mic, boundary or PZM (Pressure Zone Microphone) mic and parabolic mic (right).

The handheld microphone is just that, a microphone that you hold in your hand. This mic is usually flat black or metallic and generally has either an omnidirectional or cardioid pickup pattern. It is ideal for direct addresses to the camera by your talent. It looks good and the talent can han­dle it quite easily. It is the mic of choice for TV news reporters, singers, politicians and talk-show hosts.

The shotgun microphone is a long slen­der mic that usually has a hypercardioid or even a supercardioid (extremely focused) pickup pattern. You would primarily use this microphone in field production, mounted on a suspension mount at the end of a long fishpole. The boom opera­tor who manipulates the fishpole keeps the microphone out of the frame about 18" from the talent's mouth so that they can pick up a consistent voice level. You can use this mic to record sound effects and other sound sources because it picks up sound only from the direction it is point­ing, cutting most of the sound from its sides and back.

The lavalier or lapel microphone is a very small microphone that the talent can wear on his or her lapel or someplace near his or her mouth. You can hide these microphones in costumes or weave them into an actor's hair. If you ever get bored during a live play or musical, try to find the mics on the main actors. Costume design­ers and makeup artists are very ingenious in finding places to hide the mics and power packs. Lavaliere microphones usu­ally have an omnidirectional or cardioid pickup pattern and closely mic a single talent. You can also use the omnidirec­tional lavalier to mic various acting areas by hiding them in plants, furniture and other set pieces. Just be careful that the tal­ent doesn't touch or bang into their hiding place. You will definitely hear it.

The boundary microphone is a fairly new style ofmic that has really made a name for itself lately. This mic is mounted on a flat surface and usually has an omni-directional pickup pattern. These are great for miking conferences where you have a flat table with people sitting all around. You can use them extensively as stage mics (not placed directly on the stage where footfalls would create heavy interference) to enhance thea­tre sound levels; or use them to record a group of people in a closed environment like a class or seminar.

The parabolic microphone is for long­distance audio pickup. This extremely directional microphone looks like a small handheld satellite dish which reflects all of the sound to a center-mounted micro­phone. This mic is primarily used to record the sound at sporting events or to pick up the sounds of wild animals. Both this microphone and the shotgun microphone are ideal for picking up middle to high fre­quency ranges but are not suitable for high quality, total range sound recording.

Microphone Accessories

As with all equipment, once you find the microphone you want to use, you have to accessorize. A friend of mine who runs a recording studio isMT05 constantly explain­ing the need for the strange looking ring with what looks like panty hose stretched over it. This is an extremely important
microphone accessory called a windscreen or more precisely, a pop filter. He places the mesh surface in front of the microphone so that the talents' breath does not pop the microphone when he or she says words with hard "P"s and "B"s (see Figure 12-5).

Windscreens come in a variety of shapes and surfaces. If you ever see a microphone with a gray or other colored foam ball covering its end, you are seeing one type of windscreen. Another popular wind­screen used with shotgun microphones is a zeppelin or blimp (these names coming from their resemblance to the early 1900s aircraft). These windscreens completely enclose the microphone and are attached directly to the fishpole or mic stand. If you see someone using a big hairy microphone outdoors, he is using a blimp with a wind­jammer cover. This cover is extremely effective when you are shooting in windy conditions.

Shock mounts or suspension mounts are another extremely valuable microphone accessory. Suspension mounts prevent sounds traveling through the mic stand or fishpole from being picked up by the
microphone. Soft elastic materials like rubber or nylon suspend the mic so that the sounds created by your hands rubbing the fishpole or something hitting the mic stand are not heard. It is extremely important that you use a suspension mount when using a shotgun on a fishpole.

Mic Check

When buying microphones and accesso­ries, the kind of equipment you buy will depend on the type of production you do. Look at your needs and compare them with the instruments described above. There is a microphone designed for every type of production. It is up to you to decide what your production require­ments are and the microphone that will best fit your audio needs.