For those of you who have been following this, a major design change has occurred due to the fact that I've determined that even for native German language speakers, it's difficult to acquire the required tubes. And those who do pay so much that building an enclosure out of 3/4" MDF costs about the same, if not less! So...
This picture shows the two completed subwoofers side by side. I like this design in that they now also serve as a riser for a 3rd row of seating. The internal volume should end up just a little over 650l. Internally, I plan to use 2" wide strips of 3/4" MDF as bracing. They will be placed every 8 inches, and their edges will all be rounded. Also, they will be glued to each other at the intersections. The top of each woofer will be carpeted like the riser for my 2nd row of seating. I'm not sure how I'll finish the sides as of yet.
Also, if you look at the large version of the picture above, you will notice a diagnal cut in the MDF between the subs, The concept is that the board in the middle has one half glued to one sub, and the other one is glued to the other. The slanted cut is so that one will rest atop the other, and the diagonal cut will "lock" them together. this should prevent the enclosures from "walking", provided I don't run them out of phase with each other.
For my port, I decided to go with a 6.25" port, as I can source a PVC tube that size at local hardware stores. Also, the smaller diameter puts my first port resonance at more than double the maximum expected frequency of 120Hz.. Both ends of the ports will be flared with 1 1/2" flares. According to "Flare It", I will experience chuffing at 10Hz with a 0db FS signal. However, I expect that that point, all the other noise during such a scene will make the chuffing inaudible. Chuffing begins at just above -2db FS.
For the excursion, I do plan to use some sort of filtering. I will have to experiment, however, to determine how much and what sort of filtering I will use. My AV Receiver's LFE output is flat into single digits, with the -3db point at 3Hz. I will have to measure the output of the iNuke with an O-scope to see where it's rolloff begins. Ideally it will be high enough that I won't need a highpass due to my low tuning. But if not, I'll experiment with the iNuke's filters to see where I get best results. I do understand that the filters can't be set lower than 20Hz. However, I have read that by combining a highpass with a shelf filter, one can achieve a highpass with a lower cutoff.
For amplification, I will be using the iNuke 3000. I plan to run the speakers, Stereo Integrity HT18 D4s with the coils in series, so 8 ohms per channel. That should give me 400wpc, which is enough to get me to reference volume (300W required according to WinISD) If that doesn't work out, I'll try them in parallel, and see if the iNuke can deliver the required current. If all else fails, I'll bridge the iNuke and buy a second.
So, does anybody notice any glaring oversights, or does it look like I'm good to begin construction?