After being a professional acting coach for most of my career, I know something about the importance of a vocal warm up for actors. But for anyone who has to speak for a living, or for part of their job - a vocal warm up is essential.
Just like an athlete that warms up before competition, or a musician that warms up before performing, then the professional speaker is no different. The voice is such an expressive and important part of your job that it deserves the respect of a proper warm up.
Consider these techniques for warming up before public speaking:
A simple way to get your voice ready for a speaking engagement is simple humming. Warming up the resonators with humming helps you to bring a lovely resonant sound to your voice without too much effort. You can hum into different parts of your face, starting from your nose with your mouth open. Then onto your lips. Next, the space between your nose and top lip, you can feel it working if there is a buzzy vibrating feeling. Using a high tone while humming, you will hear your head resonator in the top of your skull. Humming is a simple way to get a lot of value out of a simple exercise.
Yawning is also great for the voice - as long as you don't over extend the jaw while doing so. By gently yawning, you can stretch important muscles in the neck and throat and release any tension from the voice.
Massaging the jaw area is another good way to warm up the voice, because tension in the jaw greatly reduces the capacity for articulation, the ability to make consonant sounds clearly.
Breath is the power behind your speech, so be learning some simple breathing exercises, you can improve your strength of projection and tone. Practising breathing in for 6 seconds, holding your breath for 2 and then breathing out for 7. This will not only relax you, but work the diaphragm muscles as you increase the length of time that you breathe in, hold your breath and breathe out for. Try adding one to each of the IN/HOLD/OUT and trying again. If you are speaking without a microphone in your presentation or public speaking event, then you will need strong projection that comes from practising breathing from the diaphragm.
You can warm up your articulation with exercises such as: