In order to get a big and powerful singing voice, the singer needs to incorporate many singing techniques together.
Furthermore, this can only be done by practicing regularly with the correct vocal exercises.
Now to open up further for bigger singing sound, the singer has to open the area near the base of the tongue. This can be down by imagining the beginning of a yawn. This imaging opens up the singing pathway, keeps the tongue in the correct position and lifts the soft palate making your mouth shaped like a megaphone. A megaphone produces a bigger sound doesn’t it?
With this mouth structure, the back of the throat will naturally open up making the critical link between the vocal tone colors of the upper and lower resonances possible. While you are singing, the inner structure of your mouth is constantly working, moving to fine tune the oral cavity until the feel and sound of any sustained note just right.
The correct position of the mouth should thus be a slight oval like the picture above, with the corners of the mouth drawn in and the jaw down. It is critical that your lips are relaxed. If your lips are not relaxed, tension will accumulate...