When you make a humming sound, using the deepest tone you currently have, with your head dipped down, your chin to your chest, you can notice something revealing. The minute you make that same exact tone, but lift your head up high, with your chin to the sky, that same tone becomes higher.

What this shows, is that tension is the answer to a deep crisp voice. A voice box can become tense for many reasons and the resulting voice can become quite squeaky or high pitched. This has nothing to do with the size of your vocal chords. When you lifted your head in the exercise above, the vocal chords were stretched tighter, causing the sound of the tone to become higher.

Think of your vocal chords like a string on a guitar. If you have ever seen a guitar close up, you will have noticed that there is a heavy thick string at the top and a light thin string at the bottom. People like Barry White could be associated with the top thick string, and average men may be closer to the bottom thin string.

But the thing is, when you loosen even the bottom thin string, it can begin to sound very deep. Despite its thickness, even the thinnest string can sound quite deep and give a low tone if it is loosened sufficiently.

The quickest way to deepen your speaking voice is to release the tension that must exist in your vocal chords, if your voice is thin or squeaky. The vocal chords are a muscle group that can easily be conditioned and trained to relax and reverberate deeply.