Module 39

Updated: 08/04/2005

Microphones

Part II
  

Handheld Microphones

Handheld mics are often dynamic mics because they are good at handling momentary sound overloads. Although they may be called "handheld," the term is a bit of a misnomer, because this type of mic is often mounted on a microphone stand.

Because these mics are often used at close distances, some special considerations should be mentioned. First, it's best if the mic is tilted at about a 30-degree angle (as shown here) and not held perpendicular to the mouth.

Speaking or singing directly into a mic often creates unwanted sibilance (an exaggeration and distortion of high-frequency "S" sounds), pops from plosive sounds (words with initial "p's," and "b's"), and an undesirable proximity effect (an exaggeration of low frequencies, to be discussed in more detail later).

Most handheld mics are designed for use at a distance of about 20-40cm (8 to 16 inches), but this distance may have to be reduced in high-noise situations. Pop filters, which are designed to reduce the pops from plosive sounds, are built into many handheld mics.

When a mic is used at close range, it's also wise to slip a windscreen over the end of the mic to further reduce the effect of plosive speech sounds. In addition to reducing the effect of plosives, windscreens can eliminate a major on-location sound problem: the effect of wind moving across the grille of typical microphones. Even a soft breeze can create a turbulence that can drown out a voice.

The windscreens shown above are typically used over the end of hand-held dynamic mics when they are used outside.

The elaborate windscreen housing shown above on the right is used with highly directional mics in the field. Often, this type of mic is attached to a "fish pole" and pointed toward the talent, just out of camera range. 
  

Positioning Handheld Mics

When a handheld mic is shared between two people, audio level differences can be avoided by holding the mic closer to the person with the weaker voice. Inexperienced interviewers have a tendency to hold the mic closer to themselves. The resulting problem is compounded when the announcer has a strong, confident voice, and the person being interviewed is somewhat timidly replying to questions.

Personal Microphones

Personal mics are either hung from a cord around the neck (a lavaliere or lav mic) or clipped to clothing (a clip-on mic).

This type of mic can be either a condenser or dynamic mic. As we saw in the last module condenser-type personal mics can be made quite small and unobtrusive—an important consideration whenever there is a need to conceal a microphone.

When attaching a personal mic, it should not be placed near jewelry or decorative pins. When the talent moves, the mic can brush against the jewelry creating distracting noise. Beads, which have a tendency to move around quite a bit, have ruined many audio pickups.

Personal mics are designed to pick up sounds from about 35cm (14 inches) away. If a personal clip-on mic is attached to a coat lapel or to one side of a dress, you will need to anticipate which direction the talent's head will turn when speaking. If a person turns away from the mic, the distance from mouth-to-mic is increased to 50cm (almost 2 feet), plus, the person's voice is being projected away from the mic.

Hiding Personal Mics Under Clothing

Often, these mics are hidden under clothes. However, great care must be taken in securing the mic, because annoying contact noise can be generated when the talent moves and the clothing rubs against the mic. Noise can even result from rubbing against the first 10 cm (inches) or so of the mic cord.

To keep this from happening, all three elements — mic, clothes, and the topmost part of the mic cable — need to be immobilized in some way. This is often done by sandwiching the mic between two sticky layers of cloth, camera tape, or gaffer's tape, and securing the tape to both the clothing and the mic.

If sheer or easily damaged clothing is involved, it may be necessary to attach the lavaliere to the talent's skin. In this case a medical surgical tape should be used.

A strain relief should also be considered in case the talent steps on their mic cord, or it becomes caught in some object as they move. A strain relief is any provision that stops the mic from being pulled away when the cable encounters tension. Otherwise, the secured mic can be abruptly pulled out of place, which, if the mic happens to be taped tightly to the skin, might result in the utterance of some non-broadcast terms!

There are various approaches to devising a strain relief. You can have the talent loosely loop the mic cord to a leather belt or a belt loop. You can coil the cord into a couple of loops and then attach that to clothing below the mic, or if one of the talent's hands are free, you can just have them hold on to the mic cord as they walk.

Mic cords are generally not long enough to reach a camera or the studio audio connection box—and that's just as well. Generally, after you attach a lav or personal mic to talent, they need to be free to walk around until they are ready to go on camera.

This is possible if their mic cable is only plugged into the necessary extension cable shortly before they are to go on camera. In fact, with the help of a floor director, more than one person can plug into the same extension cable at different times. Assuming the audio person has checked and made a record of the audio levels for each person, this can simplify the audio process.

Forced Perception

Finally, when some hidden personal mics are used, the proximity of the mic to the person's head can result in unnatural sound—and kind of sterile sound that's not what you would expect in a typical room. If you like technical terms, this is called forced perception.

Sometimes it helps to attach the mic at a lower point on the talent to allow it to pick up a bit of reverberation from the room. If several people are using RF mics in the same room, a better solution is to use all mics as close as possible to the talent, but, in addition, use a boom mic to record a bit of live "room tone." This room tone can then be mixed into all of the audio pickups at a very low level.

Headset Mics

The headset mic was developed to serve the needs of sports commentators. Normally, a mic with a built in pop-filter is used. (Note photo on the left below.) The padded double earphones carry two separate signals: the program audio and the director's cues. Having the mic built into the headset assures a constant mic-to-mouth distance—even when the announcer moves from place to place. Performers at concerts often use a much smaller and less conspicuous version of this (photo on the right, below).

Proximity Effects

Question: Why is it that even with your eyes closed you can tell if a person speaking to you is 20 centimeters or 5 meters (6 inches or 16 feet) away?

The first thought might be that the voice of a person 20cm away would be louder than if the person were 5 meters away. That's part of the answer; but if you think about it, there's more to it than that. You might want to say that the voice of a person that's close to you "just sounds different" than a person who is farther away.

This "just sounds different" element becomes highly significant when you try to start editing scenes together. Getting the audio in scenes to flow together without noticeable (and annoying) changes, takes an understanding of how sound is altered with distance.

Sound traveling over a distance loses low frequencies (bass) and, to a lesser extent, the higher frequencies (treble). Conversely, microphones used at a close distance normally create what is called a proximity effect—exaggerated low-frequency response. Some mics have "low cut" filters to reduce unnatural low frequencies when the mics are used at close distances.

When directional microphones are used at different distances, the sound perspective or audio presence (the balance of audio frequencies and other acoustical characteristics) will change with each change in microphone distance. In addition, different types of microphones and different room conditions have different audio characteristics that can complicate the audio editing process.

It's possible to correct for these things to some degree during the audio postproduction sweetening phase where various audio embellishments are added. During this phase such things as graphic equalizers are used to try to match the audio between successive scenes.  However, an exact match may be impossible. It's far easier just to keep in mind (and avoid) the proximity effect problems that will be introduced whenever you use microphones at different distances. These differences will vary, depending on the microphone and the acoustics of the location.

Mic Connectors

To ensure reliability, mic and general audio connectors must always be kept clean, dry, and well aligned, without bent pins or loose pin connectors.

The two connectors on the left of this photo are female and male Canon or XLR connectors. These three-pin connectors are used in professional audio applications.

To the right of the Canon connectors are the mono and stereo (with the floating center connector) miniature connectors. Finally, on the right of these is the RCA-type connector, which is common to most home entertainment equipment.

Most consumer and prosumer camcorders have miniature stereo connectors. Since professional microphones have male XLR connectors, an adapter is needed.

The simplest solution is an in-line adapter at either end of the microphone cable.

A more versatile approach is the connector box shown on the left, which has XLR plugs and volume controls for multiple mics. This adapter box can be attached permanently to the bottom of a camcorder.

When used on location, audio connectors must be kept dry. However, mic cables can be strung across wet grass or even through water without ill effects—assuming the rubber covering has not been damaged. If you must work in rain or snow in the field, moisture can be sealed out of audio connectors by wrapping them with plastic electrical tape.

It should be emphasized that this applies to mic cables only. If power cords are used in the field for the camera, lights, or recorder, these cables and connectors must always be kept dry to avoid a dangerous electrical shock hazard.
  

Positioning Mic Cables

Running mic cables parallel to power cords often creates hum and interference problems. The solution is often as simple as moving a mic cable a meter away from any power cord.   

Fluorescent lights can also induce an annoying buzz in audio. Computers and certain types of medical equipment, especially if they are near audio cables or equipment, can also create undesirable noise.  By carefully listening to your audio pickup with a set of high-quality, padded earphones, you can generally catch these problems before it's too late.

Mic cables can often be a problem, so in the next module we'll discuss wireless microphones.