Your voice is your direct access to the audience during a talk. Without a voice there would be no presentation. It is therefore crucial to have a good voice behavior, a proper speaking technique.
First of all, talk slowly. As a rule of thumb, your speaking pace should be 10-30% slower than normal everyday speaking pace. The reason is that the audience needs to be able to listen, understand and process the information that you provide. This takes time and as a speaker, you must give them this process time. Put in occasional breaks of 5 seconds or so to let your information sink in.
Speak with volume. A voice does not have to be loud, but it has to be voluminous. Speak ‘from your stomach’ instead of from your chest. It can give you better voice support and make your voice more solid.
If the room is big, the audience is large or your voice is quiet, ask for a microphone. Many prefer a headset microphone as this frees up the hands and makes it possible to navigate the slides and use a laser pointer. Also, holding a microphone by the hand for 1-2 hours can give you pain in the elbow.
A speaker’s voice is more important than the visual slides. If certain people in the audience can hear you, but not see you, they will still get something out of the talk. This is not the case for the opposite situation.science-communicator.com