The fundamental frequencies of speech are generally from 100-250 Hz.
Vowel sound contain a great deal of energy and are generally from 400-2KHZ.
Consonants overlap at the bottom from 1.5 KHz to 4 KHz.

Boosting the fundamental frequencies will add more bass to the voice, but too much will add a "Muddy quality"
Boosting the vowel range will add both a sense of power and energy.
Boosting the consonants will not generally bring much more energy, but are important to intelligibility and being understood.

Many choose to roll the ends of the spectrum a bit to avoid the bassy muddy boom from the voice and the high end hiss.

Hope this helps.....but sound is very personal. Your physical voice and mic placement are also huge factors.