openbox system sounds volume

[jagdpanther]

I am using Openbox and pulsaudio. I control volume levels with pavucontrol.
In the pavucontrol app I usually control individual app volume in the Playback tab or directly in the application that is generating the audio. This all works.

However, how do I control the volume so system sounds? (The volume control in the Output Devices tab of pavucontrol does work but it changes the volume for all applications.) There does not seem to be any sort of system sounds entry in pavucontrol Playback tab.

What I really want to do: cut the volume of the "drip" sound when I make a mistake in an xterm window.

Any ideas?