Formal:
* Sonorous: This implies a deep, resonant, and pleasing quality to the voice.
* Resounding: This emphasizes the loudness and clarity of the voice.
* Powerful: This describes the voice as strong and commanding.
* Authoritative: This suggests that the voice carries a sense of authority and confidence.
Informal:
* Loudmouth: This term is often used negatively, implying that the person is overly talkative and doesn't care about others' feelings.
* Bawler: This suggests a loud, harsh, and possibly unpleasant voice.
* Rumbler: This is a more playful term, emphasizing the deep, resonant quality of the voice.
* Big voice: This is a simple and straightforward description.
More specific:
* Baritone: This refers to a specific type of deep, resonant voice often found in men.
* Mezzo-soprano: This refers to a specific type of deep, rich voice often found in women.
Ultimately, the best word to use depends on the specific context and the tone you want to convey.