DPA Microphones have released a number of videos that look at the relationship between microphones and speech, there is a lot of information to help ensure that the voice remains intelligible regardless of environment, the different responses to microphone positions and more.
Please see below videos:
Why are consonants essential to speech intelligibility?
How voice directivity affects speech intelligibility?
Why is microphone position so important?
How do voice frequencies affect speech?
Understanding dynamic range and sound pressure level of the voice.
Webinar: Speech intelligibility with body worn microphone - Audio Specialist Eddy Bogh Brixen
For more facts about speech intelligibility visit the DPA Website here: