The materials used to make the soft speaker have been felt cloth, in a frame, 1mm copper thread, and sewing thread, for the analog part.
The copper I use is quite thick, since my intention was that the amplification was stronger, but the sound has not improved because of the thickness of the copper. If not the opposite.
Once the copper has been sewn to the frame, the elements to connect the soft speaker are a magnet, a battery and an amplifier.
These are the characteristics of the amplifier that I have used, which comes together with a potentiometer and a switch, in order to control the volume of the speake.
Board documentation
As seen in the diagram, the upper speaker wire is connected to one output and the back to the other output, the batteries are connected to the top, and the input is connected to the phone via a cable with mini jack output.