I know from my own TOEFL test-taking adventures that some people believe their TOEFL speaking score is based on the volume of their voice.
This is a mistake. You should speak at your normal volume. Two reasons:
- The microphone sensitivity automatically adjusts to the volume you use when you say, "I live in Tokyo, I live in Tokyo ." If you speak in a loud voice, the mic is less sensitive, and if you speak in a smaller voice, the mic becomes more sensitive. If both the microphone sensitivity is HIGH and your volume is HIGH, the recording will not be very clear. You can test this for yourself .
- You can not control your intonation well if you are speaking too loudly . Most Japanese people breathe shallowly, so a loud voice sounds like you are barking, not speaking.
Please use English well!
 When I get questions like this, the conversation is usually something like this:
Student: "I heard that I should speak loudly on TOEFL."
Dono: "That's bad advice. Who told you that?"
And it's always one of two Japanese teachers in Tokyo. Use a Japanese instructor for reading and listening, but not for speaking, even if your TOEFL score is low.
 I don't recommend that you keep repeating "I live in Tokyo, I live in Tokyo ..." by the way.
 Test this yourself at home with an IC recorder. Set the mic 録音シーン to 口述モード (LOW sensitivity) and record yourself at a loud voice, then with a small voice. Then try it with 会議モード (HIGH sensitivity). Which of the four sounds better to you?
 Unless you are an opera singer, and even then it's hard to breathe deeply enough to use your diaphragm if you are sitting down.