它是什么？

A visual representation of different dynamics.

它在哪里找到？

DIY and bring it with you.

我该如何使用它？

Move an arrow or other visual indicator to show students where they should be on the dynamic scale. If possible, correlate it to language about volume that they already know (e.g., a class might use a number or color system to indicate quiet voices, speaking for a large group, etc).