Breath
The fuel for the voice (more breath, more sound)
Accent
The way of speaking which is used in a local area or country.
Tone
The change in voice to express emotion.
Pitch
how high or low the voice is (little girl or old man)
Volume
loudness or quietness of the voice
Pace
Speed of speech
Register
appropriate speech for the person being spoken to, or for the situation (Queen vs baby)
Clarity
The clearness of the voice
Emphasis
The stress on a word or phrase
Articulation
Clear pronunciation of words
Fluency
Natural, flowing speech
Intonation
Rising and falling of the voice in speech