I just found this at PE. If I added one of these to box, would act as though it had a larger volume and thus reach lower before rolling off? I can't imagine something so simple would work...but if it did
The Scan Speak Vent is an air flow resistant, "aperiodic" damping device very useful in sealed box applications. It works by reducing the maximum impedance at the box resonance by at least 50%. This results in clearer, better defined bass, with more amplifier power and control into the lower frequencies. It also allows the use of a driver in a smaller than optimum sealed enclosure. The vent should be mounted to the cabinet back wall in a 4-5/16" (110mm) diameter hole. About 60% of the cabinet volume should be filled with damping material, being careful to leave an open path from woofer rear to the vent device. For enclosure volumes up to 1.75 cu. ft., one vent is required. http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=13501064&St=3695&St2=70038773&St3=60766601&DS_ID=3&Product_ID=7832&DID=7 
