Is there a way I can set the default alarm sound?

little better solution:

1- Say hey Siri REMOVE ALL ALARMS(due to manual will take time).

2-creat one alarm and choose whatever voice you like.

3-Say hey siri ;CHANGE ALARM TO ..ANY TIME; then slide it manually to ON with your finger due to it keeps staying off!!

I believe that, when you set a new alarm, it will default to whatever you used the previous time. At least that's the way it has always worked on my phone.