How to speak with more resonance?

Find a Good voice coach who will explain resonance - which is how vibraion moves and keeps moving - through cavities of air. [Your mouth [palate], your nose.]

This is when we can use "bone conducted sound" through the sound waves and vibration hitting the hard bone in the palate or nose or "Air conducted sound" which is when we push the air through the palate to make sound. The air conducted sound is usually produced in the arch and to the back of the soft palate which means the sound waves get absorbed into the soft tissue, whereas the bone conducted sound will bounce off the bone and is commonly known as reflected sound.

You really need a qualified coach or speech therapist in Laryngeal Biomechanics to teach you - not yahoo answers.

You need to work on your breathing technique. Please consult a voice coach who works with actors, actresses, telemarketers, teachers etc. Also, you need to try to decrease the amount of background noise as well.