I can probably answer a few of the things you have brought up to Brandon and Josh but not all of them at this point in time given the early state of the project.
I suppose the most common thing people know about horns is that they produce a higher SPL for a given radiator excursion by placing additional acoustic load on the drivers radiator or radiators in this case as there are two.
This load is presented as a higher pressure and there has been mention of throat distortion and velocity limits in the throat.
Here is the old thumb rule for calculating this;http://books.google.com/books?id=b_w...age&q=&f=false
This throat distortion is caused by the fact that the velocity of sound changes with temperature, with a VERY intense sound, the pressure side of the wave travels slightly faster than the vacuum side.. This happens because the local temperature is slightly higher on the pressure side and slightly cooler on the vacuum side.
After traveling some number of wavelengths, one finds a pure sine wave can precess into a triangle wave as the pressure side advances on the vacuum part.
In what seems like a past life now, I worked on acoustic levitation system which were flown in the shuttle and here this was a real problem.
These systems used a 22KHz signal to levitate or position a sample without contact inside a high temperature furnace in ZeroG. Levitation of a Styrofoam begins around 155dB while stone can be levitated around 165dB and lead around 168dB.
Fwiw, at 170dB, one can ignite a cigarette with acoustic friction (air rushing in and out of the tobacco).
Anyway, here a few tidbits which I found on line if curious.
I was filmed once demonstrating acoustic levitation in a movie called Mystery of the Sphinx back then but couldn't find the clip on line.http://adsabs.harvard.edu/abs/1988MTA....19.2619Rhttp://www.google.com/patents/about?...=0&as_maxy_is=http://www.sciencemag.org/content/vo...5455/cover.dtl
The bottom line, normal throat distortion is not an issue with bass horns normally as the difference between the highest and lowest frequency is small and the sound pressure level is not high like the >>155dB used in levitation.
20 plus years ago I had developed Servomotor driven subwoofers called Servodrive, while working at the same company (they let me start a small speaker division at Intersonics).
They provided a data point as well because there was NO high power motor related Xmax or nonlinearity like a VC driver. At rated power, the BT-7 horn system produced less than 1-2% THD. Bottom line, bass horn distortion is nearly all driver related / caused. If you saw Garth Brooks, Michael Jackson, U-2 or Deaf Leopard etc in the 80's, you heard these cabinets on tour.
So far as drivers, we are sending the 12 inch driver we use at first, there are other drivers that will work but in part this depends on physical fit and parameters.
I was thinking we would offer ours and as we confirm others have those on a list of ones that work also. Ours is an all out push on a lab 12, a driver I specified for another DIY horn I designed for pro sound some years ago.
It has a 3 inch VC and 15mm Xmax and has a very strong radiator happy with a high compression horn loading.
The Velocity in the throat is also not high enough to cause choking like ports a vented box can exhibit as well, to understand why, you need to picture a horn in action.
Horns in the most compact form are a quarter wavelength long, a quarter wave resonator or horn has a closed end and an open end.
For this condition, the closed end is a velocity minimum the open end a velocity maximum. The air motion at the driver end is approximately the driver excursion times the compression ratio (difference in radiator area to throat area)
Thankfully, the large end of the horn is also where the velocity is highest so choking is not an issue.
Is there a maximum output?
Of course, that is a frequency dependent thing and not determined by measurement yet.
Also, on the measurement, we normally measure at 10 meters when we have large enclosures, for the measurement that shown, this was at one meter because the amplifier in the measurement cart was most unhappy driving a low Z load at low frequencies.
This could be gotten around by using a different amplifier, hooking the drivers in series or using two channels, none of which were an option standing in the parking lot at the time. There will be more data taken but yesterday there wasn't time to re-wire the box.
So, what you see was 1W nominal into 2Ohms (1.4V) and 1 meter distance.
What I can say now is that at 100W input, the predicted excursion is less than 5mm at the largest point, if that tracks properly, Xmax is first reached around 1KW around 16Hz..
Perhaps a better way to view that is where (what SPL in half space) do you reach Xmax with what your used to, relative to adding say 26 or 30dB to the measured level, reflecting an input of 400-1000W and keeping in mind you will have some room gain and corner loading extension indoors.
Ivan and the guys will be beating on it at the shop (a actually a very large room) later and will know more about it's practical upper limits soon.
Yes it is big, so are the wavelengths involved, the two are related.
On the other hand, placed against the wall like how RMK had used his spud's some months ago, behind the screen, they aren't that big and should be able to cause the desired genuine panic response to the uninitiated.
As Ivan mentioned, I don't think we will supply plans, the issue is partly that these are high pressure cabinets that depend of being very ridged with no air leaks.
We are supplying Baltic Birch fully precision CNC'd with dado's for all joints and pilot holes drilled to minimize the chance to get inferior results.
I am keen to get feedback from Brandon and Josh as they build the first two kits, they gave a lot of good inputs on it in he design phase so it will be cool to see what they think when they have the smell of fresh Baltic birch in their living rooms haha.
I grew up building Heath kits and Knight kits (allied radio) and at least for me, I like the idea of people doing things a lot.
Anyway, back to work for me.
Hope this helps fill in some blanks.