Currently, all members can create a temporary voice room by default. To create a temporary voice room, click on the + Create Voice Room button, and then type in a name for the voice room.

After everyone leaves the temporary voice room, it will stay active for about 10 seconds, and then it will be removed.

Admins can restrict who is able to create temporary voice rooms. Under Settings > People > Roles, edit a role and disable the Start Voice Rooms permission to prevent members with that role from creating rooms. See Roles and Permissions in Heartbeat for details.