You use an airstone & air pump for a bubble source instead of using the venturi. There are some threads relating to the mod, I can't remember where they are. It's pretty simple; lose the venturi air intake (do this by just cutting the airline to a point below the filter's internal waterline, or take the airline completely off), route the airline down the outside of the chamber gaining access to the chamber using one of the bottom vents, put a wood airstone on the airline inside the base of the chamber, attach the other end of the airline to the pump and there you go. An air valve between the pump and the airstone will give you airflow adjustment. This will help with the noise but the efficiency won't improve much. There's just so much you can do with that short of chamber.