Michael, you don't have to say it out loud. Now Master Lin says that a beginner (like me) can say it out loud. As you practice more and deeper you can say it in your heart. He doesn't say subvocalize; eg. in your head.
I like vibrations that are setup in my chest and heart when I say the ohm. When I do it out loud I place my tongue on the roof of my mouth when I inhale. I do the same thing when cycling (moderately) and breathing the universal energy at the same time. I do it along nice safe bike paths and eyes open.
You are perfection.
Iam2 
