The most common microphones used in induction loop systems are 'electret' lecturn, handheld, boundary and lavalier microphones as they have the highest tolerance of magnetic feedback. Best practice (though not always possible) is to place the microphone(s) as close as possible to the speaker.
Dynamic microphones should not be used as they contain moving coil magnets which can be affected by the magnetic field generated by the loop.
A method that is sometimes suggested for overhead placement is a ceiling-mounted boundary microphone. This should be used with caution as (a) microphone too far from the desired sound source, especially in the case of a high ceiling and (b) the ceiling in buildings of modern construction is often an extremely noisy location due to air handling noise, lighting fixtures and building vibration.
Phantom power is provided on all PDA amplifiers so electret microphones with batteries are not necessary.
