This means the Spirit is in control of your tongue and your spirit is in control of the volume.
Almost. We always have the choice to stop and start our tongues. The Holy Spirit propels the words, but we make choices to form them. And the more I pray in tongues, the more the pace seems like talking with expressions, pauses, ups and downs. And more of a sense of tandem Spirit:spirit activity.
I find almost a sense of obedience in knowing what words to form -- listening/being in tune, responding with word formation.
He who believes in Me, as the Scripture said, From his innermost being will flow rivers of living water.
-John 7:38
It is not really about the words. Language is just a social form of expression. It is the language that offends people, but God deals with the heart of what we are asking and saying. He knows all the languages, and doesn't need to hear how we phrase our thoughts. People do.
Assuming that God leads us to pray for situations we don't know the whole story behind (and don't need to know), then our yieldedness and willingness to pray allows Him to pray through us to activate responses (ask, seek, knock, find).
There were times God led me to pray in accents of different regions, and I later found news stories on injustices and wars in these regions.
YOU CANNOT deliver a "Message in a tongue" to the church "just because you feel like it"
This seems to be at the heart of what Paul is saying. Tongues/other languages were useful to deliver the gospel in the languages of the visitors present for the census. When there are not many speakers of other languages, the congregation does not need other languages spoken. If God chose to deliver a prophecy in tongues, which I have seen before, then someone must be ready to give a translation. Maybe people got carried away after it happened the first time, and tried to replicate the experience.
I have to admit that I have been in Charismatic meetings where I have felt someone was about to prophesy, and also knew the gist of what they were going to say. The Holy Spirit gave me a split-second understanding, as though He might be training me for something where I would need to know.
At those times I felt compelled to pray in tongues, and did so to myself -- knowing it would not benefit anyone much to hear the tongues first. I sensed the tone, pace, determination behind the message and it seemed very much like translators work -- the speaker propelling the translator.
I'm not looking for commentary on this-- just wanted to explain some experiences in response to the OP.