OK. After a little bit more refining of the model, I made some sawdust and took some measurements.
I'll cut right to it - how does 27-90 Hz. +/- 3 dB of 90 dB @ 2.83 volts sound?
After working out the impulse response and phase issues discussed earlier, the model was revised a bit more. Once I was happy with it, I made a sketchup diagram of a single-folded tapped horn that matched the model as closely as possible.
It's nothing special, it just allowed me to figure out the dimensions and cut-list. If anyone wants the actual file, PM me an email address.
Then - it was time to make some sawdust. Let's just say that it has been a little while since I built a sub - and it shows. It is certainly not a thing of beauty. Ultimately, in translating the model to MDF, I missed a few measurements slightly, and I also had to allow for an access hatch to install the drivers. I measured what I built, then revised the model to reflect the reality. I also broke in two new MCM 55-2421 drivers and measured the Thiele-Small parameters of the pair, as well as an older one that I had sitting around. All three measured very similarly. I averaged the parameters of the two I used and entered that into Hornresp.
Here is the final input screen:
Here is what I measured (2.83 V, 1 Meter, groundplane)
Here it is compared to the model:
Well, it appears that all the bumps are in all the right places, and are a little bit flatter than the model predicted, though the response is also down a few dB from the predicted SPL (which could be my meter or measurement technique, my mic and meter are not perfectly calibrated).
I also ran an impedance sweep with my Woofer Tester 2:
Looks like the resonances may have attenuated the high Q peaks. The slight shift in frequencies could be due to the straight line measurements I used when I calculated the path length.
Anyhow - in a nutshell, this little exercise completely met my expectations and nearly matched the predictions of the simulation. While the drivers may not be ideal for use in a tapped horn, they certainly perform as predicted.
I've not really had a chance for any sort of subjective listening yet, I barely got the basic measurements done and plotted up today.
Let the armchair quarterbacking begin.