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
Video 1. Hertz Experiment on Electromagnetic Waves by Ludic Science (2015) Source. Simplified recreation with cheap modern equipment. Uses as transmitter power source both:
and the signal is observed on the receiver with a neon lampVideo 2. Hertz and Radio waves Explained by PhysicsHigh (2016) Source. Simple schematics showing the basics of the experiments. No choice of components rationale.
Ciro Santilli