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 omni-directional or shotguns and lavaliers versus handheld and boundary mikes? Throughout this column, 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 of 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 mikes, 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 mike variables.
Most microphones fall within one of the two major families: dynamic or capacitor (condenser) microphones. The dynamic microphone has a fixed 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 Figure 1).
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 mikes 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 mike s ability to record high quality audio. Dynamic mikes 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 mike 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 hand held 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.
The 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 Figure 2).
The condenser microphone has a number of attributes that are important for the videographer to consider. The condenser mike 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 mike. 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 mike 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 mike. Fortunately, most microphones that you would use for field production have a battery space built-in. You just have to remember the batteries.
Whether you choose either a dynamic or condenser microphone, you must also decide the best pickup pattern for your production. There are four primary pickup patterns to choose from: omnidirectional, cardioid (or unidirectional), hypercardioid (or shotgun) and bidirectional (see Figure 3).
The omnidirectional microphone picks up sound in every directionfront, back and sides (see Figure 3a). 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 mike.
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 . This pickup pattern is excellent for voice mikes and miking musical instruments.
The hypercardioid microphone picks up only sound from the front and is very directional (see Figure 3c). 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 mike (Figure 3d). You would use a mike with this pickup pattern primarily to record two voices talking into the same microphone. You can also use it as part of the MS Stereo Miking Pattern discussed in last month s Sound Track column.
You can find all of these 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 mike.
Styles of Microphones
After 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 mike on screen. The major types of microphone styles are: handheld, shotgun, lavalier or lapel mike, boundary or PZM (Pressure Zone Microphone) mike and parabolic mike.
The handheld microphone is just that, a microphone that you hold in your hand. This mike is usually flat black or metallic and generally has either an omni-directional 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 mike of choice for TV news reporters, singers, politicians and talk-show hosts.
The shotgun microphone is a long slender mike 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 that manipulates the fishpole keeps the microphone out of the frame about 18" from the talents mouth so that they can pick up a consistent voice level. You can use this mike 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 some place 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 mikes on the main actors. Costume designers and makeup artists are very ingenious in finding places to hide the mikes and power packs. Lavaliere microphones usually have an omni-directional or cardioid pickup pattern and closely mike a single talent. You can also use the omnidirectional lavalier to mike 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 of mike that has really made a name for itself lately. This mike 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 mikes (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 long-distance 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 mike 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.
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 is 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 they say words with hard "P"s and "Bs.
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 mike 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 mike stand or fishpole from being picked up by the microphone. Soft elastic materials like rubber or nylon suspend the mike so that the sounds created by your hands rubbing the fishpole or something hitting the mike stand are not heard. It is extremely important that you use a suspension mount when using a shotgun on a fishpole.
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.