It's not difficult to figure out why your first build bit the dust quickly. The loading 'seen' by both drivers in your initial design is an acoustic short circuit - the same as a dipole loudspeaker. The distances between your 'taps' in the waveguide are not large enough to create significant phase differences between the diaphragm motion and the wave arriving at the tap as it passes down the waveguide. As a result, your drivers were probably way into overexcursion, and would eventually have ripped themselves to shreds. Much of what you might have been hearing from the enclosure would have been motor distortion - the woofer's final cry for help before mechanical damage or failure.
Hornresp does not do a good job of simulating the fact that the radiation surfaces in the 'taps' are mechanically coupled. It only simulates two separate radiators out of phase with one another. Otherwise, you would have seen extreme excursions in your diaphragm displacement plot in Hornresp.
The first build had problems from the simple overlooking on my part of whether a block of wood was properly glued up or not. That first fold also wasted a great deal of space. The second fold was almost perfect in it's use of the box area and the fold area. It has been performing every day since last June.
I think you miss the entire design concept.
This is a bandpass speaker. The rear chamber is a tuned resonant chamber vented into a flared port that acts as a vented front chamber. The rear chamber has the bulk of the drivers pressure response. The rear chamber is tuned to the low end of the pass band by means of the narrow vent that you can see in between the two triangular sections. The front chamber has been sized to act as a tuned vent that resonates at about 120 hz.
There is no short circuit what so ever. If your asumption was correct you would have the same problems with any vented enclosure. Because that is what the rear section of the UNHORN is. A vented enclosure. The front section provides some gain at the top end of the boxes response. Changing either section volume will lter the rsponse of the system. Changing the size or length of the coupling vent area will drastically change the response.
It works within 3 hz of the simulation done in Hornresp. And performs within a db or two of the simulated efficienct. I have nothing but confidence in the abilities of Hornresp to model things correctly when you understand fully what you trying to model. And to clarify one more point on how horn resp models multiple woofers. It adds the surface area of the drivers into an equivalent circular piston. It models this larger piston as one driver. THe two colors you see are the front and back of the driver.
As long as the two drivers are within a 1/4 wavelength of the frequency they are to function in, it does not matter that they are separated by a small distance. A quarter wavelength at 30 hz is a bit more than 8 feet. The drivers are less than 3 inches apart. That a quarter wavelength of 512 hz. Not bad!
Again this is not a magic box that solves all the problems. It is a clean sounding subwoofer that lets you hear more of what was in the recording and less of it's own built in thud and boom. You can actually hear the difference in bass note timbers and tones. Something that is not heard to often.
In the first build, the inner driver is absolutely seeing a short circuit. The only way to acoustically load a driver is to make sure the rear of the driver never 'sees' the front side of the driver, or 'sees' the radiation from the front driver with the phase rotated to within 90 degrees of the rear driver - or else some part of the interaction between the front and rear of the driver will be destructive. In your first pictured build, there is less than two inches of baffle between the front and the rear side of the inner driver, which is absolutely a short circuit because there is no acoustic structure in the enclosure 'circuit' between the two sides of the interior driver.
I discussed this with you on DiyAudio - in your original build, you might as well omit the interior driver entirely. Hornresp's excursion predictions are invalid in this case because the exterior and interior drivers are not mechanically coupled - Hornresp simulates all the drivers in the system working as a single piston, not multiple diaphragms.
Second, the design has been up in smoke for 6 months.
Now for a minute consider an open air subwoofer such as the Celestion dual 12 inch design back about 20 years. It had an even greater " acoustical short circuit" and yet it managed to produce great deals of bass. So be a bit more careful in what you consider to be absolute and true when it comes to acoustics.
Yes it was done back in 1987. I had hair back then. LOL
Third I redesigned it and presented the redesign.
The redesigned version is a product of me figuring a better folding scheme. That is 95% of the difficulty when making a horn.
So seeing that you are right.
What about talking from a point of view where you have listened to the box and can comment about the sound?
That would be more fruitful. There are a couple out there pounding away daily. The gentlemen who built them are happy campers.
One more thing.
To say that I'm a discriminating listener is just beginning to explain my listening process. I played in the back row of the orchestra for six years. I know first hand what the instruments sound like. And even though that was 23 years ago I can still tune an instrument, any instrument by ear. I have what I call almost perfect pitch. I know in my head what a note sounds like before it is ever produced. I can tell you sharp, flat, and even shades in between. Ruthless is the right word for how I am when it comes to properly reproduced sound.
What does this matter to you?
Well if I give a speaker the thumbs up it is indeed tonaly accurate. I did not report on the other levels of work I underwent to make this weird box. But I played with the design until it could carry a tune properly.
If you have any interest I review classical music for:
I do organ, harpsichord and baroque music. Obviously organ music pushes subs hard. And I have some of the nastiest low bass notes on recording. Any recording. And yes I have tried them out on the UNHORN2. And yes they were produced to SPL levels that made one guy who I built a SDX15 monkey coffin for shake his head in amazement. These drivers rock. :hsd: