be wrote :
"...Loking at the pictures it seems to me that you are using felt in front of the chamber front plate to seal the coupling between the horn and the chamber? This could cause some problems if the felt sheat is open towards the horn throat..."

Hello be,

Thanks for your advice (and for the compliment).

You are correct, the felt is between the mating faces of the removable chamber and the horn. However, the hole in the felt is the same size as the throat of the horn, so the only part of the felt that is "exposed" to sound pressure is that which is found on the inner edge of the hole in the felt seal (about 3.5mm when compressed). Did you understand that this was the case?

"...My experience with placing felt in the throat area is that it is very effective in making the sound go flacid.
Maybe, to avoid possible problems, you could use a rubber o ring or some corck?..."

Though I have not detected any "flaccidity", using another material here would be simple, and would remove any doubt. Before doing anything, I might try crawling up into the horn and covering the edge of the felt seal (the part that's exposed to sound pressure) with aluminum tape; this stuff is should allow bridging the 3.5mm gap with enough rigidity to get an idea.

jd*

Jessie, a few comments.

The back chamber mechanism is good. Are you planning to do the same in the midbass horn? Since you most likely will not drive your upperbass all the way down I think that the back chamber mechanism  will be more effective at your midbass. Be advised that the driver will generate a lot of pressure in there and the sipping of air will reduce the effectiveness of the back chamber. I do not say that it will be bad if the pressure will be losing from it but I say it will change effectiveness. Also, do not forgets that most likely you will end up with the ultra low size of back chamber when the vertical back wall sitting to the driver magnet will farm already too large chamber. What you might end up doing is to glue to the back of the slideable wall a space-killing indentation that would have a contra-template of the Fane driver. This would effectively to push out the air from the driver sided. I would put even some filing into the driver frame’ holes… Also, turned John Hasqiun to your, Jessie, project and he pointed a very valuable point that you might overlooked. He suggested that this design shell have a way to vent the back chamber as it being adjusted, otherwise he will over or under pressurize the woofer cone and damage it.

The entire speaker looks very nice. Well thought and well executed. There are a few comments still. It feels that there is very little room for the tweeter to breathe. It is not the narrow firing tweeter and I think you might give to it a little bit more room. The frame that holds the Fundamentals Channel is is kind of odd esthetically. It looks like it was not from there. I do not know how bone-firm and how heavy your Fundamentals horn, but is it does need some support and cannot just to hang then you might consider to  use a harness around a horn and a single rod from the top of the frame to the horn. What I am trying to say that the support of the Fundamentals Channel might be more elegant…

Going for exponential midbass is probably good idea; most likely I would do the same if I go for 50Hz horn, I would most likely go for rectangular of for a shape with 2-3 straight side and 1-2 curved, juts for sake of esthetes. Unfortunately talking about the masking “appearance” of midbass horn it is is impossible to do not consider the given real-east envelopment. Since you, Jessie, live in rented apartment and most likely will move (well, when you finish you system they will kick you out of the building anyway) then you might consider to make the double-action midbass horns. What I mean is that pretend that you horn is 8 feet. So, you make the first 5 feet from the throat is firm and solid and the last , the most larger 3 feet, detachable and perhaps with odd edge profile. The next time you move and realize that your horn would block your entrance in bathroom, or the corner of the horn blocks a half of your window and look to prominent on the room then you juts change the termination part of the horn…

It is very interesting to see what you do Jessie, in contrary to many audio people I know who just endlessly run their mouth on audio subjects you actually do the things. It is very stimulating to observe you progress. Whan you finish then bring your installation to a city with good FM programming and you will be getting from high-end audio and much as it possible to get from it.

Daniel J. Plach (AES E-Library) wrote:
"...The use of hyperbolic-exponential horns makes possible practically any desired resistance or reactance characteristic near cutoff. The hyperbolic-exponential horn allows much more uniform transmission down nearer to cutoff than is possible with the exponential type..."

???

"...You might consider to make the double-action midbass horns. What I mean is that pretend that you horn is 8 feet. So, you make the first 5 feet from the throat is firm and solid and the last , the most larger 3 feet, detachable and perhaps with odd edge profile. The next time you move and realize that your horn would block your entrance in bathroom, or the corner of the horn blocks a half of your window and look to prominent on the room then you juts change the termination part of the horn…"

Yes this is probably a good idea, but I may have a difficult time with it knowing that 1/3 of the horn is missing. Also, I am free to base future real estate decisions on the dimensions of the finished system. One very real constraint is making sure the parts will all pass through the door of the place where the horns will be built.

Construction plan :
In order to make the walls of the horns rigid enough, without going into the kind of weight that only cranes can move, I have decided to make the flare (everything down stream of the driver mounting plane) like a surf board; meaning from a composite sandwich consisting of a double layer of glass fiber, then 2" of rigid urethane foam, then another two layers of glass fiber. The result should be a fairly light-weight non-resonant structure. The back chamber (meaning everything up stream of the driver mounting plane) will be made using the same materials that went into the other horns (hemp-reinforced refractory plaster, in this case, having a wall thickness of around 3").

"...It is very interesting to see what you do Jessie, in contrary to many audio people I know who just endlessly run their mouth on audio subjects you actually do the things..."

Well I will say that it does entail sacrifice, but what is being sacrificed in my case is really no big deal. One of the things I have been telling myself all throughout the course of this project was that (contrary to some of the other ball-and-chain projects with which I have burdened myself) this one will be a really nice thing to have should I manage to live to retire and grow gracefully old. Though I don't have a turn table, when you wrote about your "End of Life Phono Corrector", I understood exactly what the title meant.

jd*

Paul,

Thanks for the comments.

I may have come up with a way of making the BIG horns fairly painlessly.

I found a place that sells large sheets of urethane foam in several thicknesses and several densities.
And, Its no big deal to find a place that can do laser cutting based on sections generated via a CAD program.

So the plan is to buy sheets of 4 inch thick low density foam, send it to the laser cutter and have them cut out sections (imagine the horn as a loaf of bread), which I would then glue together to achieve a rough horn shape, having a stepped transition every 4 inches.

These transitions could then easily be made to flow, by knocking off the peaks with a SurForm (cheese grater) file, and connecting or bridging from one glue joint to the next, making sure to leave the joints untouched by the file (as they are representative of the original section used to guide the laser cutter).

The resulting smoothed out foam horn could then be laminated with resin and glass fiber from both the inside and the outside. It would of course be too big to fit through the door, and laminating up inside the throat would be a pain, but this is just to illustrate the principal.

In practice I would have each section (which would look like a rectangular frame) cut into four "L" shaped pieces, making it possible to assemble just a quarter of a horn; an object of manageable dimensions, easy to attack with the SurForm file, as well as to laminate, because it is open (no crawling up into the throat). The quarters of the horn would then be bolted together to form the complete horn.

This is a moldless technique... The texture of the glass fiber will be apparent. The guys that used to make surf boards this way spent days sanding and filling in the texture so as to have a clean support onto which they would airbrush images of topless mermaids. Like the other horns, these will be paintd flat black; I will nevertheless keep the fiber glass work as neat as possible.

With regard to resonance, this technique may not yield the sort of "deadness" that masonry or really thick wood might give, but as the foam I've found is not the really rigid (and expensive) stuff, it should make quite a dead core, especially for its light weight.

jd*

Here is a better shot of Ulf's horn... In this image, the object on the right is the core of the mold, which corresponds to the inner surface of the horn :

Jessie,

When I spoke that I would go most likely for exponential I did not mean the Exponential vs. Hyperbolic but rather that it would not be a Tractrix. I have no specific preferences for Exponential, Hyperbolic or any other long profiles. A common sense suggests then the longer profiles shell be better for lower frequencies but in my case such a statements would not be backup by any of practical experiments. Frankly speaking even among the people who do use long horns it is also VERY difficult to make a definitive assessments about which long profile is better. At the “frequencies of the interest”  (40Hz-150Hz) the coupling with a specific room is way too important and it is virtually imposable to make an objective and methodologically clean assessment what profile is better even if someone one would have two identical long horns in the same room (can you image someone so courageous?!!)

So, if I was in your shoe I would discard whatever Romys and others say and would talk to the guys who build the horns. Talk to John Hasquine, talk to Jeffrey Jackson, talk to Bruce Edgar, talk to Martin Seddon, talk to the Le Cleach guy (I do not remember his name but he is your cosine and you shell know)  Bruce is particularly a subject of interest as he has a lot of practical and theoretical experience and he also personally has a very good discrimination for the results. You will not sense this discrimination if you will be his client, Bruce knows that his clients are mostly deaf idols who can’t distinguish results anyhow, but it does not mean that Bruce does not know how to make the things better and his advice would be voluble. Do not take anything that anyone say as the fact but rather use it as background to make you own decision.

You are engaged in a serious project. Why don’t you to let people to bid for the idea of your midbass horn. If I were you I would compile a resume of my being built acoustic system attached with request for people to come up with ideas of a “honest” 45-50Hz horn. I would even install some kind of prize for a most beneficial suggestion…  I would do in the end anyhow for whatever I personal would feel works out better but it does not mean that I would not listen many other who might some experience in the field…

Truly unexplored in the field of bass horns. There are zillion of new composite of syntactic light and very rigid material out there that might be a good candidates for building horns. People nowadays learned how to make good performing carbon fiber musical instruments like this for instances:

http://www.luisandclark.com

So, way do not leans hot to make “interesting” horn with proper balance of damping and “Resonance Oops” properties? I do not say that it is a good direction to think but the benefit would be so cool: to have a quick and light, literally collapsible bass horn that could be installed for a few seconds. It might be a wall ornamentation in living room during a “normal time” but when you wish to listen music a few walls might be unfold and the bass horn might be formed. I would even go for such a stupid idea as inflatable horn. Sure it will resonate; the inflatable resonances should be included into the design… somehow…

Anyhow, there are so many opportunities and unexplored interesting territories in bass horn design. No one unfortunately works on “divert options”.  I understand why… :-(