I replaced the stock speaker in my Behringer Bx600 (I know, I know..) with a Madison Warrior 12'' driver. While I had it down I played around with WinISD to see if I could improve upon the porting. I could not find the optimum port dimensions for the measurements of the cabinet so I guesstimated. I covered the shelf port on the bottom with aluminum angle and coated the inside of the amp with automotive undercoating/sound deadener (stinky!) I used (2) 2'' PVC juntion box reducers for the ports. Along with the speaker upgrade I feel these ports have made a vast improvement over the old shelf port. The cabinet is punchier and more defined. Instead of the amp farting out with a B string, the house now rattles like crazy. After all this it is still a cheapo amp, but it does sound a heck of alot better.