They are not opposites in nature, any speaker is a microphone too - perhaps "acoustically transducic" although its a horrible phrase sums up the idea better.
The difference between a microphone and speaker is what they are optimized for - a condenser mike is a small electrostatic loudspeaker, a dynamic mike is a small dome tweeter...
The difference between a microphone and speaker is what they are optimized for - a condenser mike is a small electrostatic loudspeaker, a dynamic mike is a small dome tweeter...