subvocal reading and comprehension

I am an average reader who can absorb large amounts of info if required but generally I read every word and recently realized (rather acknowledged--as one becomes suddenly aware of one's nose in the mirror) that I seem to hear the words I am reading. While recently reading a rather large volume for research, a comment was made by the author about comprehension. He noted that slower readers hear subvocally what they read, as if a voice were speaking in their head. I confess that sometimes if I am really enjoying a book--I switch to a voice that I have enjoyed in the past vocally. For example, Patrick Stewart or Lorne Greene. I also read some things that are 'dry' in blocks of words sometimes with voice-- usually without--reading only enough to understand but not for enjoyment.
Is this a standard of reading that I should consider changing so as to improve comprehension? I do not seem to have have trouble comprehending reading in thought form but if this is why I sometimes must go over some passages more than once to reassure myself that I have understood what I have just read--and also sometimes to see if I can glean more from the passage--or just enjoyed it--perhaps there are more efficient ways of reading that I have not explored.