A powerful voice is vital to speaking in public. Your message is literally projected through your voice, whether big or small. You must speak up to be heard and, importantly, to be understood. I must admit that some really good speeches come from people with soft voices. But this can only work if you're in a quieter environment. In most cases a big, booming, and resonant voice is key to getting your audience's attention and keeping it.
Various techniques can help to improve your volume which in turn gives you a commanding voice. Be sure to embody strong posture. Your voice will carry farther when your back is straight, shoulders are back, and chest is out. Also, be sure you are using all of your space on the stage. The audience will hear you better when you are closer to them. You can even visualize your voice carrying through the air and reaching all the corners of the room.
You must also learn how to breathe from your diaphragm. Try this to see the difference - put one hand on your chest and the other on your stomach. The hand over your chest will rise if you are breathing from your chest. Your other hand on your belly will rise when you're breathing from your diaphragm. You must understand this difference and practice speaking from your diaphragm to really make the most out of your voice.
Another benefit to diaphragmatic breathing is that we tend to do this naturally when we're relaxed; and breathing deeply is one of the most relaxing things we can do.
Have you ever been around someone that speaks so softly that you can hardly hear them unless you're right next to them? On the other end of the spectrum, have you heard someone singing to a full audience without a microphone? It is astounding that two individuals with the same equipment (lungs, vocal chords etc.) can use it all so differently. Breathing and posture play such a big role in this difference.
As important as all of this information is, I don't believe it really gets to the heart of the matter. The biggest obstacle to speaking loud and clear, in my view, is related to apprehension. A major symptom of anxiety is shortness of breath and constriction in the throat. This completely takes away your capacity to speak.
We may also have a preconceived notion that it's rude or strange to speak loudly. It feels uncomfortable. To overcome this, try to speak louder than what feels comfortable or natural. You must give yourself permission to speak up.
By all means, take advantage of volume increasing exercises. Get accustomed to speaking at an appropriate volume around large groups. Get involved in meetings, organizations etc. Acting, singing, or improvisation classes would certainly help. Either way, if you really struggle with speaking up, an important barrier to overcome is the fear of being loud and in charge during your speech.
We may also have a preconceived notion that it's rude or strange to speak loudly. It feels uncomfortable. To overcome this, try to speak louder than what feels comfortable or natural. You must give yourself permission to speak up.
By all means, take advantage of volume increasing exercises. Get accustomed to speaking at an appropriate volume around large groups. Get involved in meetings, organizations etc. Acting, singing, or improvisation classes would certainly help. Either way, if you really struggle with speaking up, an important barrier to overcome is the fear of being loud and in charge during your speech.