Lavalier Microphone Mounting Techniques

Lavalier microphones are attached differently depending on the nature of their use. For instance, in theater applications where the microphone is used to amplify an actor or a singer's voice, lavs are typically concealed in their hair. This eliminates the possibility of scratching against their clothing while they move, which would result in the amplification of the scratching sounds as well. It also adds to the suspension of disbelief, since the characters themselves would not be wearing microphones, especially if the plot is set in a time before lavalier microphones existed. Occasionally, specially-designed skin-color headsets known as "headworn microphones" are used in stage applications when actors spend a good deal of their performance singing and moving around quickly (such as in stage musicals and in lecture or presentation scenarios). A headworn microphone is essentially a lavalier on a stiff wire mount which loops over the talent's ear.

In television and documentary applications, the lavalier will typically be clipped to the subject's clothing, such as a tie, jacket or collar. In narrative motion picture usage, lavs are almost always hidden under clothing to conceal the fact that the person is mic'ed. The Boom microphone typically sounds 'better', more natural than a lavalier mic and is always a soundman's first choice, however oftentimes for exterior location shooting, it may be more practical to use a lavalier. One such situation would be during a wide shot that forces the boom operator to keep a distance with his microphone from the speaking talent that isn't close enough to achieve a good signal to noise ratio. In that instance a lav mic hidden on the talent due to its proximity can achieve good signal to noise ratio for recording of speech. When lavalier microphones need to be concealed under clothing, the possibility of material scratching against the microphone is a certain risk. To minimize this, sound recordists might wrap the head of the microphones in moleskin or place it inside a hollow centered column-shaped sponge and place it under a placard, behind a button, or within the knot of a tie. The transmitter pack which the microphone is attached to may also need to be hidden under a person's clothing. Transmitter pouches are held on with elastic straps and hold the transmitter in various places, hidden wherever the clothing provides a non revealing space, i.e. high around the waist in the space created at the spine just above the belt line, inside the thigh under a skirt or dress, about the ankles under a pant leg, or even on the inside of a boot.

Lavalier Microphone Mounting Techniques Source :
http://en.wikipedia.org/wiki/Lavalier_microphone