Notes for when running on the Raspberry Pi with the Rasbian Buster OS.
When using Java 11 OpenJDK, you may find the audio from the Text To Speech coming out the HDMI port instead of the selected 3.5mm Audio socket on the side of the Raspberry Pi.
This is caused by Pulse Audio not following the requested settings and routing the audio from the Java apps to a different output, the HDMI like it or not.
The solution is to edit the Java sound.properties file.