Ciro Santilli Heinrich Hertz's main initial experiment used a spark-gap transmitter. It is not something that transmits recorded sounds like voice: it only transmits noisy beeps. And as such was used for
Hertz Experiment on Electromagnetic Waves by Ludic Science (2015)
. Source. Simplified recreation with cheap modern equipment. Uses as transmitter power source both:- a piezo igniter from a barbequeue lighter
- a more powerful home-made transformer
Hertz and Radio waves Explained by PhysicsHigh (2016)
. Source. Simple schematics showing the basics of the experiments. No choice of components rationale.