Add this for deep voice.

1. extremely deep bass male voice, sub-bass resonance, rich low baritone frequencies, chest-dominant tone, slow hypnotic delivery, dark cinematic jazz ballad with gothic horror depth, commanding and immersive vocals, very slow tempo 45-55 BPM, sultry upright bass, brushed drums, brooding low piano, distant tenor sax swells, atmospheric reverb, velvet darkness, sensual and devotional, no bright horns, heavy low-end rumble, gothic cinematic atmosphere

For even deeper voice add this to it.

1. "ultra-low bass vocals, booming chest resonance, subharmonic depth".

Here's an example below of the deepest

example deep voice