This is sometimes known as a personal microphone or a 'tie-clip’ mic, although it is rarely
ever clipped to the tie these days.
It is also sometimes known as a 'Lavalier microphone' after the Frenchwoman
Madame Lavalier who was famous for her big boobies. Sorry, the big ruby she
wore round her neck.
The original Lavalier
microphone, in similar fashion, was hung round the neck rather than clipped
The modern miniature microphone is usually of the electret design, which
lends itself to very compact dimensions, and is almost always omnidirectional.
Miniature microphones are used in television and in theater, where there is
a requirement for microphones to be unobtrusive.
Since the diaphragm is small and not in contact with many air molecules, compared
to a conventional mic, the random vibration of the air molecules does not cancel
out as effectively as it does in a microphone with a larger diaphragm.
Miniature microphones therefore have to be used close to the sound source;
otherwise noise will be evident.
The reason why, in TV news, the miniature microphone is often clipped to the
clothing with the diaphragm away from the presenter's mouth is to avoid the
slight risk of popping due to P and B sounds. Since the microphone is omnidirectional,
it doesn't matter which way it points.