This is, for the time being, my second category of voice in horror/the horror in voice.
The spectral acousmatic voice is a voice that is nowhere. It has no perceivable source of this world, but it forms a haunting presence. I expect this will be quite a large category as it is used as voice is commonly used a stand in for entities that require presence but not body - ghosts, the dead, spirits etc.
The Woman In Black (1989)
A wonderful film - acousmatic screams, voices and laughter are in their traditional horror roles as hauntings and spirits. The phenomenological doubt of audition and memory is a leverage for horror too. The fog distorts sounds, did you hear a scream or did you hear something like a scream?
Candyman is slightly odd in that it could be argued that the source has a location, but then Candyman is not necessarily a physical person - more a haunting hallucination, a spectral demon perhaps. Nonetheless the voice of Candyman is totally outside the frame, it is a deep narration voice - and deeply unsettling. It is either an internalised horror of the characters fears or a sonorous presence from another world (the afterlife?) - in this sense I would argue both instances are acousmatic. The horror in this scene dissipates quite remarkably when Anthony Todd's visible, moving mouth is tied and synched up to his omnipresent call, just before the nightmare ends.