Jessie, there is another solution that you might consider, that might be viewed as compromise for one-side as might not be view is compromised from other side. If to allowed ourselves to close eyes to midbass timing-integration and if the geography or your room would allow then I think it would be rational, also to think about corner-loaded sub-45Hz.

When you build horns you will be able for use your installation in a way how used my Macondo, upperbass horn crossing all the way down. Then, when the midbass will be done you will lift up the crossover in your upper bass horn. In this scenario the lower you go in your midbass horn the more interesting result you will have.  So, the corner-loaded midbass will half more timing problems will have more cavity colorations but it will also allow you with a relatively it simple expenses to go for 35Hz-40Hz region. I have to tell, that it is not so clean to me what I would choose if I were doing the project myself.

In this decision, it will be something that you might not considering yet - you do not know how the specifics of your room will handle ether your straight  45Hz or the hypothetical 30Hz corner-loaded horn. Read my article about the “Embedded Micro-Positioning”. It might be extremely brutal. You might have a perfectly performing 45Hz straight horn that you will hang above your installation, but the horn will output nothing, literally nothing. The irony will be that considering the geometry of this 45Hz you will not be able to move it, as moving it even 6 feet away will have practically no effect.

So, here is the best investment in your upper bass horn that I might propose you can do:  in 10 days, during your Assumption of the Blessed Virgin Mary holiday, put your wife in front a specter analyzer and explain to her what to look for. Attach 40-200Hz bandpassed little sealed speaker to a tall 10-15 feet pole and a run across your room like a wounded in ass gazelle, while your wife is looking at the spectral analyzer is in results of your movement. You might do it yourself as well, if you use computer-based RTA then you might output the results to a large side TV. Do not forget make the same experiment for the different microphone positioning.  This way it will not give you exact picture how “it” will sound in your room, but it will secure you from making large strategic mistakes or perhaps help you to discover a more winning topology in your given case.

No matter what you will be doing, if you have your room as your ally then it will be much better than to have your room as your foe….

A tractrix and a exponential horn was compared in a AES paper sometime 1950-1970, I dont remember when exactly.

The two round and straight  horns where made with the same theoretical cut off frequency, something like 100Hz, they had the same mouth and throat diameter, hence the exponential horn was somewhat longer.

The measurements was made under open sky on a roof top.

The results in the low frequencies towards the cutt off  was clearly in favor of the exponential horn, it had a rather smooth and civilized roll off, while the tractrix was rather uneven and ragged, the usefull range was extended maybe a octave lower.

Tractrix is nice, but it is only a reasonable connection between one space angel and a small area and 180 degrees and another larger area, the theoretical basis is based on geometry and some charming but faulty asumptions on wave propagation.

A much more sound shape is the oblate spheroid horn invented by Earl Geddes.

It is actually possible to get comercial horns with something I think is an near oblate spheroid shape and a nice 180 degree termination at German ebay under the name ”Jabo”

The price is really reasonable.

The manufacturer ironically calls them ”Kugelwellenhorner” witch is German lingo for Tractrix horn.

Regarding the shape of dazzies horn: I can only see a decorative reson to make it round, I dont believe that round is better than rectangular in this range, in fact a rectangular shape will make a much better coupling to the room boundaries possible and extend the useful range 1-2 octaves lower, depending if dazzie can place it against a floor (or ceiling) and a wall.

Romy the Cat wrote:

"...Let pretend that some kind of company take the Jessie’s idea under the wing and begin to commercialize it..." "...I really think that someone who is willing to be in the business should look at the Jessie’s idea of frame-motherboard and take it further..."

Paul S wrote :

"...Jessie, you know I am not a horn guy. I played with horns for 5 years, and I have heard plenty of them, and so far none have worked for me, musically.  But I have remained mindful of horns' potential, and I keep coming back to that, for various reasons..." 

Paul, first thanks again for the input, and second, watch out...One of my objectives in pursuing this project is to get you back into horns!

"...Perhaps you could figure the circumference of your big horn at given lengths and thereby turn the form(s)/mold(s) in sections..."

Ok I lied when I said "no the large horns will not be turned"... I am able to turn big chunks, and at one point was thinking (once again) exactly as you suggest (are you a Taurus or what?)... The original construction process I had in mind was in fact to turn one 1/8th segment of the large end (see CAD images in previous posts)... Regardless of the final material used for the actual horn, I still may end up "turning" the mold from plaster.

See below a large chunk of the tool I turned/molded (keep wanting to spell it like in French "mou...") for the Upper-Bass horn :

Above : The clients visiting my workshop checking on progress... On
the table is part of the tool I use to make the Upper-Bass horns... It is
turned and molded... From here I make a 2-piece "female" copy, into
which I load the plaster and hemp for the actual horn.



Above : Same but end view (the photo is sort of pixelated, making the horn
look rough... In reality it is not... I however really do look this rough)


Above : Same but showing interior (on the right is the internal forming
tool, which serves only once, so its constructino is rather thin by comparison;
just enough to do the job one time.)

BTW, these are my disposable "horn-making-clothes"... In all future photos
you are likely to see me wearing these same clothes, until I throw them out...
The plaster does not come out in the wash.

"...Of the large horns I have heard, tossing out the plywood ones, only two were concrete (one poured in place, one gunnite), both "exponential", neither worth the effort, IMO, and I'm sure you would agree if you heard them. One was round, one was rectangular (no parallel walls, however).  I do not suppose for even one second that the "exponential" profile was "the cause" of the problems..."

There are many reasons why they may not have been effective, however, I would suspect throat diameter as the most often over-looked criterion.

jd*

be wrote:

Regarding the shape of dazzies horn: I can only see a decorative reson to make it round, I dont believe that round is better than rectangular in this range, in fact a rectangular shape will make a much better coupling to the room boundaries possible and extend the useful range 1-2 octaves lower, depending if dazzie can place it against a floor (or ceiling) and a wall.

Well, I do not think that it would be as much as 2 octaves but rather a .5-.7 octaves at it’s max but still the point is extremely valid. Unfortunately I do not think that there is a final judgment on it. I would also intellectually agree that round might not be better than rectangular in this range but what for our intellectual analyses would be the definition of “better”?

If a round bass horn is crossed at 240Hz with a second order then I would question that rectangular horn is the ultimate shape. The problem is that the differences might (or might not) be only in the very fine details of imaging, that it VERY difficult to judge or to compare. Even if someone would make, let say 100Hz, round and rectangular horns then it would be also very difficult to observe the imaging differences as this range the relationship between the horn and room would be too influential.

So, if I were doing that project I would not care about “decorative reasons” or “imaging rational” it will be no conclusion in there anyhow. I would rather ask myself: how many times in life a person has guts, stupidity, conditions and courage, not to mention the wife’s blessing, to build a round 45Hz horn? I never seen anyone who did it twice but I have seen very many people who did it zero times…

Still, being adult and pragmatic, and taking under consideration that you “be” is very correct - with boundary loading I might consider the following: if I go for segments (let say 5-7-9-11 segments) and then if I decided to ceiling-load my horn then I would NOT need to remake the horn but only to change the bottom profile of one or two segments. I think it would preserve the “decorative objectives” of the roundness but at the same time it would be utilitarian enough to serve the might-be-changing RTA’s objectives.

Jessie, I’m very ignorant in materialology but I have a “common sense” concern. I do not see that you imbedded into your plaster construction any tightening points from a stronger material. I mean: the holes in plaster – how strong you will be able to tight the bolts before the plaster will give up? Did you think what you will be using for the bolts or studs bases?

Rgs, Romy the cat

Erik,

The high pressure zone near the throat does not create distortions; the distortions (the turbulence of the wave’s front) are created right after that zone (according to William Hall, MIT, 1932, though no one said hat he is right). Also, it is very much frequency-related and at relatively low frequencies the waves propagate very linear across the horn. Do not forget that we do not have linear dependences between the horn size and the wave length…

Moreover, Erik, the AES experiment that you described unquestionably was very interesting but let look critically (my favorite mode :-) to what went on there.

You said: “two round and straight  horns where made with the same theoretical cut off frequency, something like 100Hz, they had the same mouth and throat diameter, hence the exponential horn was somewhat longer.”

There is something in this experiments that make it methodologically not kosher for me as they did not equalize the conditions. The exponential horn is longer then conical or Tractrix and if all those horns have the same mouth’s and throat’s diameters then the exponential will have larger volume of the horn bell and consequentially the larger amount of air inside of the horn. The larger amount of air produces more air mass and consequentially creates higher throat reactance. From now, it will only depend from what kind of driver the horn uses. With a driver that has a relatively low diaphragms mass (any compression driver for instance) then the minuscule change in the throat reactance will be sufficient to change the cone’s damping and certainly the sound of the entire horn. So, if we have different horns, with different air volume, use the same drivers and they are wiling to compare them, then the drivers’ resonances shell be also equalized. Here is where another problem hits – as soon you begin to EQ the driver’s resonances then the drivers begin to change sound; to change sound depends what other methods of resonance EQ you have chosen. Therefore you do not observe anymore the sound of identical horns of the different profile but rather you hear two fundamentally different sound producing sources.

I personally, dealing with horns do not use theoretical bases to observe what happen with them and I tend to use purely empirical ways. It is my believe that NO one TRULY knows what the hell it going on with horns and no one has any idea how a driver will sound when it will be horn loaded. Just listening the thing, developing better listening understanding and compiling it into more and more accurate listening evaluation techniques I think is more beneficial then knowing the theory about the horn operation.

Romy the Cat wrote:

I personally, dealing with horns do not use theoretical bases to observe what happen with them and I tend to use purely empirical ways. It is my believe that NO one TRULY knows what the hell it going on with horns and no one has any idea how a driver will sound when it will be horn loaded. Just listening the thing, developing better listening understanding and compiling it into more and more accurate listening evaluation techniques I think is more beneficial then knowing the theory about the horn operation. Rgs, Romy the Cat

Marcus, my opinion about it does not change.

Any systematic methods of simulation of horn driver/horn systems are true only within a scope of very specific coordinate systems that was chosen for predictions or simulations. It is wonderful for patent applications, for writing PhD theses or for participating in intellectual discussion about horns operation, or perhaps for better understanding roles of drivers but unfortunately no one of those people who do it ever was able to associate their research with actual Sound. Sure, the systematic and conceptual methods might prevent some rudimental mistakes but those people never (at least I did not see) were able to make Sound better in term of it human/musical nature.

I am sure it would be a lot of people who disagree with me but what important to understand is that I do not built in my mind an abstract knowledge base about horns. My interest about entire horn subjects is as deep as it has relation to the very practical Sound that I am able to experience and as long it serve my auditable interests. All the rest conversations about horns, although I perfectly acknowledge their rights to exists, are just do not attract my interest.

By distortion in the throat I mean distortion caused by the nonlinearitiy of air that manifest itself by high pressures.
I dont think this was known in those days.
If this makes any significant audible difference in this particullar case I dont know, but I wanted to compare a somehow comparable Tractrix with an Exponential, since there was some concern on  Jessies behalf regarding this.
Turbulence does not cause distortion as amplitude nonlinearities does, maybe it should be termed noise? Is this really a problem?

You are absolutely right that the conditions of the experiment can be questioned, and maybe comparing two horns of same volume or maybe same length would be more significant to our practices.
You can make the tractix to go as low as an Exponential, but then it would have a larger mouth diameter.
On the other hand in many cases the maximum allowable horn diameter can be the limiting factor and then the little AES paper is very helpful.

I agree  again, one cant predict how the result is really going to be unless you make the horn and listen to it in the intended set up etc. etc. but lets hope we are not completely blind and can make some reasonable predictions with our minds and whatever other means we have.

be wrote:

By distortion in the throat I mean distortion caused by the nonlinearitiy of air that manifest itself by high pressures.

Erik, I do not see why higher pressure atomically implies nonlinearity. Gas pushers its walls very linear in all directions and, as I remember from my high school, the nonlinearity of pressure come only from the nonlinearity of temperature and volumes. Mostly likely you refer NOT to “nonlinearity of air that manifest itself by high pressures” but to the nonlinearity of jointing the profiles of horn and internal waveguide of a compression driver. This does take place but I never seen anyone bitch or even care about it beside me…. (Read my Vitavox  S2 with electromagnet thread)

be wrote:

I dont think this was known in those days.

You would be very surpassed what know in those days… :-)