Steve - Yea I came across the term LLT and have been looking into that. I've always been in the ported camp but sub 30hz is presenting issues I've never really had to worry about and I'm not trying to build gigantic boxes. Honestly considering a 2'x4'x2' box was a bit to swallow especially since I plan to do dual subs.
diy speaker guy - Post 26 is the exploded view of the cabinets I built and put pictures up of; the 2.5cuft @ 31hz, 3.5x3.5x24 ports x2 + a third inside for the ABC with the chambers split 2/3 and 1/3 with allowance for the sub volume.
I've tried to see what is better than WinISD but most of the info is from 2015 and earlier and you're the first to say it's a POS. I'm not saying you're wrong as I have no grounds to personally say one way or the other but I've used it because from everything I've been able to read it's usually regarded as a good program. Anyway I have generally leaned towards larger boxes and smaller ports but after spending some time with Excel and deriving some formulas I realized there is an 'ideal' box volume for a given port cross sectional area when considering simply the box volume and port volumes. Obviously that will have to be tweaked for the dead volume from the wood. For example at 9hz and 20sq in total port area the least amount of volume will be ~2.75cuft for the box and another 2.75cuft of port volume with the ports being 262.5". Conversely if you wanted shorter ports with the same area say 107" length you need about 6cuft for the box and 1.25cuft for the ports. Option 1 total 5.5cuft, option 2 total 7.25cuft.
I like the info on the flared port as port resonance is something I'm concerned about now.
As for those speakers I recently built I modeled them at the 2.5cuft 31hz and modeled a few more up to 58hz but I forgot to size the ports based on the 58hz velocity and no WinISD can't do ABC; I just approximate it with multiple models since as I understand it it's like having that volume from the tune to 1.9x the tune. Maybe I have no idea what I'm doing but I tend to think I have a decent grasp on what I'm doing considering the amount of time researching and building I've got into this over the past 15 years. I'm not saying I have all the information or what I've worked off of is completely accurate especially since I've never had the equipment to go back and measure what I've built. I do know that nothing I've built has stood out as sounding bad and everyone that has listened to anything I've built has been impressed but I take that with a grain of salt since they don't have a lot of experience. The best indication I've had that I was on the right path with my thinking and construction was having a stereo shop owner who did all the custom cars for CDT Audio be impressed enough with my first car sub which was an ABC box using a $50 Pioneer 12 and $100 300w Profile amp running on speaker level inputs and stock cassette radio that he gave me an aftermarket deck to install just so he could hear it with semi-proper connections. I also got to meet with one of the designers from CDT (that stereo shop owner made that happen) and he too was impressed.
All I'm getting at is I have the skills to build pretty complicated things and the intelligence to design but I'm limited by information and tools which is why I'm here trying to get information and be pointed to better tools. If WinISD is such a POS then what do you suggest to use even if it's just for standard ported and sealed boxes that aren't limited like you said to small boxes wrt wavelengths? Do you have a suggestion for modeling ABC boxes as well since I like building them? Do you have any budget recommendations for a mic and software so I can start fact checking my own builds?
I'm not necessarily targeting a specific frequency or sound level. I'm trying to accomplish a comprehensive movie watching experience. I do have some personal limits such as I'm not willing to go larger than a 2'x4'x2' box times 2 for dual subs. I also have societal limits such as neighbors and for the time being roommates. Even when I was back in my house in Texas for my last job, I couldn't get away with turning up my generic Technics 3 way loudspeakers. I literally had the next door neighboors call the city AND the cops on me. Granted they were just grumpy people but I can't imagine how to get away with 4 18's regularly unless you had either extremely good sound control or you lived on some property with quite some distance to your neighbors and you had full say so of what goes on inside the home.
I am going for dual subs because I've read it helps even out the sound reproduction, I would consider more as well down the road but after I get the rest of my speakers up to standard and a good receiver.
My main goal is clean, accurate sound with some SPL as I have always aimed for in car audio; SQ>SPL. I want to build something that has some extra horsepower so to speak but isn't a funny car sitting in the garage waiting to be used on the weekends.
If you have the time I'd be interested to see a simulation like you mention. With regard to this long road, challenge accepted. Please show me how I have a long road in front of me to do even a simple ported box considering I already understand most of the fundamental relationships between adjusting different factors and the carpentry skills to build quite a bit. I'm all about it man, if you have the knowledge and experience and are willing to share I'm willing to learn, that's the only reason I get on forums like this.
Please let me know though about suggestions for the mic and software and better modeling software as well.