You are right, I can see how some examples could help.
Here is one search for people with issues: https://www.youtube.com/results?search_query=vocal+techniques+to+help+with+speaking+problems
This one is particularly helpful with a weak voice: https://www.youtube.com/watch?v=eBN0lCTMfLw
For singers and actors, just do a YouTube search for Vocal techniques for singers and there are a ton.
There is a tool I use that is very effective for singers and actors and will help others who are just struggling to speak. It's called a Voice Straw. It's perfect for rock or other hard hitting singers. If you're a voice artist and need to scream for video games, it will save your throat.
(Not an affiliate link)