The Most Important Voiceover Tool - YOUR VOICE.
Everyone wants to know about equipment, equipment, equipment. And we’ll cover all that fun. Before we do that, there’s something equally, if not more important – TECHNIQUE. The way you use your voice, mouth, and the rest of your body. Your equipment will reflect your technique, and there is equipment that’s better or worse for different techniques.

Let’s begin with the single most important tool – your voice. You can’t speak without vocal cords, and no one ever talks about vocal cords! By understanding how your voice works, you’ll develop some insight in how to best develop it as a voice actor.
In humans, vocal cords, also known as vocal folds, or voice reeds, are folds of tissue in the throat that create sounds through vocalization. That means, when you pass air over them and move your mouth to control the sounds. They’re open when you’re breathing, and vibrating when you’re speaking or singing.
Groups of harmonics, with are basically a bunch of sound waves at slightly different frequencies combined together in a voice sandwich, known as formants, play a role in the vowel sounds produced by the human voice. Vocal formants arise from resonances in the vocal column, and are what make your voice sound human. Harmonics, formants, and resonances are kinda hard to fake, being one of the primary challenges to developing synthetic speech. The vocal column is about 7 inches long, on the average, with its lower end at the vocal folds and its upper end at the lips. Like a reed, or like lips at the mouthpiece of a wind instrument, the vocal folds function acoustically as a closed end, so that the vocal column is really a closed-tube – like a musical instrument – with resonant frequencies of about 500 to about 3,500 hertz, plus a little harmonics a little lower or higher on the scale. When a voice is produced, all harmonics are present in the spectrum, but those near the resonant frequencies of the vocal column are the loudest. Your resonant frequency is essentially your normal or natural or unforced voice. You can change that frequency by changing part of your instrument, like pushing more or less pressure down on your throat or chest, and that will change your frequency, or your voice! Very helpful for doing characters or multiple voices.
Most people have several ranges including:
SUPER DEEP
LESS DEEP
NORMAL
HIGHER
HIGHEST
Did you know your voice changes TWICE during your lifetime? Once at puberty, and once when you start sliding down the wrong side of that hill. See this very interesting Ted Ed video about it here. Play with your voice! Have some fun with it! Explore the many different things you can do with it. I think you'll be quite surprised.