There are several ways to control the volume of the bones. Here are two of them.

STATIC VOLUME CHANGE
The closer you hold to the center of the bones the quieter they become. Most of us cannot change this position without stopping play for a moment to re-position the bones.

DYNAMIC VOLUME CHANGE
With practice you can let the rolling bone slip outwards allowing the bone to slid up and down on the lower half of the stationary bone as it strikes. This gives you control of the volume while you are playing.

You can also mute the bones with a bandaid or small rubberband (like the kind that come around brocolli) where the bones come together. Your significant other will be forever grateful.