I have a 410 cab that blew a couple of speakers. I also have a 210 cab that has great tone, but lacks a little in the volume department...partly because it was ported for different speakers than what is in there now, so I don't turn it up too much. So...I have these two Eminence BP102's (10") speakers. What I am going to do is load them into my 410. Using some plywood, I'll block the other two speakers holes and the rectagular tuning port at the bottom (as this port won't work for these speakers anyway). It's not permanent...it can always be reversed when I get the blown speakers replaced). In the plywood (right in the middle of where the speaker holes are covered), I'm going to mount two 3" ports (that are currently 4.5" long). According to WinISD, this 410 is actually a better fit volume-wise than my 210 for my two BP102's. The volume of my 410 cab is 8793.5 cu. in. (accounting for internal bracing and other displacement). The BP102's like 2.26 cubic feet per speaker (or 4.52 cubic feet for both), so this cab at 5.09 cubic feet cab actually gives them more space than my 210. According to WinISD, using two 3" ports, I could tune it to 39Hz with a port length of 2.6 inches. This would keep the SPL up around 94 db with my low E (I only play a 4 string)...and it it is pretty flat all across the spectrum at 94 db. With the ports left at 4.5" long, I can tune it down to 33 Hz (which is unnecessary using a 4 string bass)...plus with it tuned to 33 Hz, the SPL drops to 91 db on the low E...and it really starts taking the plunge in decibels at 50 Hz. Across the rest of the spectrum it only hits a max of 94 db, starting at 100 Hz. My question is, should I try to tune it to 39 Hz? That seems to be the sweet spot for tuning and giving me the max db's. Also, how accurate is WinISD and it's port calculations? I've found it to be a bit off with my last two cab builds (of course, being relatively new to cab building...I'm sure I was a little "off" as well ). Just curious what others feel about WinISD's port calculations. Obviously, I'll start with longer ports and cut them down as I test them. Anyone else have any opinions on porting this 410 (made into a temporary 210)? Remember these are the 8 ohm BP102's, and there will be two of them wired as a 4 ohm cab (and it will have a tweeter). I know it's a large 210 cab, but it's of a temporary nature.