The desired sound source for a lavalier microphone is a speaking (or occasionally singing) voice.
Undesired sources include other speaking voices, clothing or movement noise, ambient sound, and loudspeakers.
Balanced low-impedance output is preferred as usual. Adequate sensitivity can be achieved by both dynamic and condenser types, due to the relatively close placement of the microphone.
However, a condenser is generally preferred. The physical design is optimized for body-worn use. This may be done by means of a clip, a pin, or a neck cord. Small size is very desirable.
For a condenser, the necessary electronics are often housed in a separate small pack, also capable of being worn or placed in a pocket. Some condensers incorporate the electronics directly into the microphone connector.
Provision must also be made for attaching or routing the cable to allow mobility for the user.
Placement of lavalier microphones should be as close to the mouth as is practical, usually just below the neckline on a lapel, a tie, or a lanyard, or at the neckline in the case of robes or other vestments.
Omnidirectional types may be oriented in any convenient way, but a unidirectional type must be aimed in the direction of the mouth.
Avoid placing the microphone underneath layers of clothing or in a location where clothing or other objects may touch or rub against it. This is especially critical with unidirectional types.
Locate and attach the cable to minimize pull on the microphone and to allow walking without stepping or tripping on it. A wireless lavalier system eliminates this problem and provides complete freedom of movement.
Again, use only high-quality cables and connectors, and provide phantom power if required.
A condenser lavalier microphone will give excellent performance in a very small package, though a dynamic may be used if phantom power is not available or if the size is not critical.