Speakers convert electrical energy into sound waves.
The electrical energy comes from an amplifier. An amlifier is required to boost the signal from its current source because the orignal current is too weak to render audible sound. Amplifiers use transistors to take a weak signal with a certain frequency and amplitude and puts out a signal with the same frequency but with a larger amplitude, making it a stronger signal. The electrical current generated from the amplifier travels through wires to the terminal strip. The current then travels through the flex wire to the voice coil.