When I didn't answer, she made herself clear and did not keep her voice down.

For a change, he also kept his own voice down.

The old man kept his voice high enough for the other children to hear.

She kept her voice at the same level as his.

She said she'd thank him to keep his voice down.

He had to work to keep his voice under control.

You'll also want to keep your voice low and level.

He kept his voice low so the others wouldn't hear.

Only say what absolutely has to be said and then keep your voice down.

It was all I could do to keep my voice down.