I built a 85 liter Shiva with a 4" port. I must have ordered the wrong port from Parts Express or they sent me the wrong one. The one I received is 11.5" totall length and flared on both ends. The numbers i came up with indicate the port length should be 13.87" to tune to 20-22 hz. Does this sound right? I tried the 11.5" port but it seems to be a bit boomy. Should i get the longer port? I tried to plug the port but it really effects the output. It somewhat tighter though. What length 4" port should i be using?