“If you can’t hear me, you’re too loud.” This is from the Whisper Principle, or Gentle Parenting, or other similar philosophies which emphasize mutual respectfulness between parents and children. When I had the opportunity to be in a day-care setting, I used the phrase, sotto voice, of course, and as our classroom relationships deepened, soon I only had to say the phrase once before the children settled down.
I love to see- and hear- enthusiastic play! Children and their boundless energy inspire me to relish my world. When it is time to transition to a slower, quieter pace, I let it begin with me. A simple deep breath takes me to a more relaxed state because I am a grown-up with at least a semblance of self-discipline. 
Children’s extrinsic motivation can be a starting point to develop a stronger intrinsic motivation. This is the beginning of self-discipline and a balance of both intrinsic and extrinsic motivation shows maturity.
When it is time to calm down, I calm down. I use calming tones and phrases, and try to bring the power of the group together in order to make a purposeful change from high activity to low activity.