Subvocalization is a mental whispering that goes on in the head, and it's hard to get rid of completely. You can only read about a hundred and 50 to 200 words a minute out loud quickly. If you're reading at two, 50 or 300, even as your base level, you're not reading every single word. So by learning how to calm the mind, be it through mindfulness techniques like meditation, yoga, tich breathing practices, something that can centre you will greatly benefit your reading.