iPadApps4School.com I featured an app called Too Noisy that shows students how loudly they are speaking. The app measures the volume of the noise in a room and displays a meter indicating whether or not the the room is too noisy. If you don't have an iPad, you can find the same basic features in the following browser-based tools.
Bouncy Balls shows students the volume of the noise in your classroom by displaying a set of colorful bouncing balls. The higher the decibel level goes, the higher and more frequently the balls on the screen bounce. To use Bouncy Balls simply go to the website, click "begin bouncing," and then click the microphone icon to allow the site to access your computer's microphone.
Calmness Counter is similar to Bouncy Balls. The difference is that Calmness Counter displays a dial meter to display the decibel level in your classroom. You can adjust the microphone input sensitivity directly on the Calmness Counter screen.
Applications for Education
Projecting either of these meters for all of your students to see could be a good way to help them understand the appropriate volume for conversations while working on group activities in your classroom.