Hare Krishna Prabhujis and Matajis,

I have been following the Krishna path through ISKCON for the past 8 months and I have sometimes had challenges chanting out loud. I know the recommendation is to chant vocal and I respect that suggestion but my vocal cords get sore very quickly - I have thick cords - and it is easier to continue silently in my mind. Through silently I can hear the vibrations much clearer than through a hoarse throat. I have tried drinking water and such to soothe the throat. Is silent japa still effective as out loud. Surely there must be other devotees who have conditions that prevent vocal chanting.