Question

I was told that to increase the amplitude of a speaker, I need to make one more efficient. How do I do that?

Answer 1

Max power is transferred from one circuit to another when the output impedance of one is equal to the input impedance of the other.

Answer 2

Assuming the speaker is a moving coil type, increasing the flux density in the gap between the voice coil and the pole-piece will increase the efficiency of the speaker. It is not usually practical to do this to an existing speaker.