I made one of these back in 1970 or so. It was inside of a coffee can using the lid for the speaker.
This class A power LED driver works good for making a speaker from an audio output transformer and any sheet of steel, even a coffee can with a steel cover.
Strip the transformer and remove the ‘I’ laminations, leaving the ‘E’ laminations. Connect the speaker leads of the ‘E’ in place of the LED. Power up the class A power amp and connect it to a radio earphone output. Then hold the three ‘E’ lamination poles about 1/8 inch or 3 mm away from the steel sheet, like the side of a washing machine. The steel sheet will transduce the audio.
