Sorry I can’t write German but can read and speak it perfectly.
I wanted to share some videos of my testing with the free NextGen Windows Program I developed in combination with the smallest Bluetooth speaker I could find. With NextGen you can use ESU sound files and run them on your laptop or pc and control a loco as if a loksound decoder was built in. Because normally the sound will come from the pc or laptop, Bluetooth is the way to bring it to the loco. The best way to show the sound synchronization is with a steam loco. The Bluetooth speaker is hidden under the sheet in the wagon.
The cheapest loksound there is