Lavalier mics are used to record an individual’s lines of dialog. Placing a lavalier mic should be done with care to avoid creating unwanted noise and to capture a clean recording of the talent.
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Lavalier microphones, or ‘lav mics’ for short, are invaluable for recording dialog from the talent, but they require some care and attention when being set up or the recordings will be marred by ‘microphone rustle’ caused by clothes or hair rubbing the mic. Plan to take a few minutes positioning and checking a mic before shooting; problems caused by rushing this can be difficult or impossible to fix in post.
It is best to attempt to hide the microphone in the outermost layer of clothing, and usually the best overall position is somewhere in the center of the sternum. If a microphone is buried under too many layers, particularly under heavy jackets, the sound will become too muffled to be coherent. This does limit options, but with a little care it is usually not too hard to find a suitable place. A good rule of thumb is to place the microphone about the same distance away from the subject's mouth as the width between the tip of your thumb and tip of your pinky finger when outstretched.
Approximating mounting distance of a Lavalier microphone Image: Light Sail VR
There are two types of microphone rustle. The first is noise from material touching and rubbing against the microphone directly, and the second is the sound of material making noise nearby and being picked up by the mic. To avoid the first problem it is best to attach a microphone to clothing rather than skin so the mic moves with the material rather than the material moving over the mic.
Sometimes, however, this can’t be avoided, such as when a character is wearing a thin t-shirt and the mic would be seen through the shirt. In this case, attempting to attach to the skin would be recommended. Alternatively, in this example, have your character wear an undershirt and mount to that). It may be possible to attach the microphone to a thin shirt by hiding the mic behind a pocket in a pocketed t-shirt or camouflaged by a screen printed logo or design.
Other common issues mounting lavalier mics include men with hairy chests and women with low cut tops. Chest hair can cause a rubbing noise that mics can pick up. If this is a problem try to have the talent wear an undershirt to act as a barrier to the hair. For women with low-cut tops, if they are wearing a bra, try hiding the mic in the middle with it peeking out of the top. Make sure the mic isn’t completely covered. It may be possible to tape the mic to the bra.
Wherever possible the sound mixer should be monitored for these problems during shooting, as clothes can shift.
Mounting a lavalier inside a button down shirt Image: Light Sail VR
Microphones vary in shapes, sizes and colors. Strong double sided tape can be a very effective solution for mounting a mic. There are also lightweight microphone mounting solutions such as URSA Mini-Mounts and RM Mounts, and there are specialized mounts for hiding microphones in ties or behind buttons. Which is best will depend on the brand and type of microphone being used.
When mounting a microphone, remember to consider where the lav cable will run. Sometimes an ideal position for the mic might not work because the wardrobe is tight fitting or the color of your wire can be seen through the wardrobe. If this is the case, try running it around the side of their body, down seams and so on to minimize the chance of it being seen by the camera.
Monitor the recording
Even with all these suggestions, nothing is 100% fool proof. Experiment with placement and techniques as there are many variables, including clothing style and material, and even body shape. Check with headphones before and during shooting, trust your ears, and don’t be afraid to change approaches if rustling or other unwanted noises become apparent.