That is what I was essentially saying that it does not have to be read out loud it could be in private as well. Many saints prayed it privately.
If you are just praying the rosary for devotional purposes, you can pray it the way you want, and God will hear the prayers.
But if you want a plenary indulgence for saying it, you need to meet the conditions specified by the Vatican in the Enchiridion of Indulgences. The Church sets the rules for indulgences and you need to comply with them. You don’t just make up your own rules.
What “many saints did” is irrelevant to the specific conditions set forth by the Vatican in the current Enchiridion, which only dates back to 1968 so any saints before that would not have even been operating under the current conditions set forth for indulgences.
This thread is asking specifically about rosary INDULGENCE, not about just saying the rosary as a private devotion, so you are incorrect in saying it’s okay to just pray it privately and/or silently, as that’s not what the Vatican said in its Enchiridion of Indulgences.
The Enchiridion of Indulgences specifically states this regarding plenary indulgence for the rosary:
A plenary indulgence is granted if the Rosary is recited in a church, a public oratory, a family group, a religious Community, or pious Association; a partial indulgence is granted in other circumstances.
The Enchiridion of Indulgences specifies that you must “recite” the rosary to get the indulgence, which means out loud. They include specific exceptions for those who cannot speak, so it’s pretty clear. We’ve had this discussion before on CAF.
You can say the rosary in private for the indulgence if you have a “family group, religious community, or pious Association” to say it with; otherwise you need to go to a “church or oratory”.
These are the rules as set forth by the Vatican. You also need to pray at least five decades “continuously”.
For further discussion of the provision, here is a helpful EWTN article
http://www.ewtn.com/library/liturgy/zlitur509.htm