Loudspeakers are without doubt the most inadequate component of the audio signal chain.
Everything else, even the microphone, is as close to the capabilities of human hearing as makes hardly any difference at all.
However, amplify the signal and convert it back into sound and you will know without any hesitation whatsoever that you are listening to a loudspeaker, not a natural sound source.
Loudspeakers can be categorized by method of operation and by function:
Method of operation:
In this context we will use 'PA' to mean concert public address rather than announcement systems that are beyond the scope of this text.
Moving coil loudspeakers are the 'ordinary' everyday variety. The drive unit works like an electric motor, but instead of going round and round, pushes in and out.
The electrostatic loudspeaker works by similar means to the way you can charge a balloon with static electricity by rubbing it on some suitable material, then once charged you can stick it to the ceiling. Electrostatic loudspeakers are not common, but they can deliver excellent sound quality.
A direct radiator loudspeaker is, once again, 'ordinary'. That means it doesn't have a horn. A horn loudspeaker has a flared tube attached to the front that improves its efficiency and makes it louder.
The priorities of loudspeakers differ according to their various functions...