In reply to my post:

Romy the Cat wrote:

The epoxy carbon-kevlar and glass fibers staffed with damping? I wonder how more fun would be if they staff these hollow horns with sand, I would…. I had once an idea to have a very soft sand horn using sand-filled air balloons as the horn walls….

 I got an email:

Dear Romy, why not simply use sand?? Have you been to a metal foundry? They make moulds of some resin impregnated sand. Just add a little extra resin, expoxy or something and it would be quite strong and have a surface...

I was thinking about it: what a phenomenal idea!!!

If you ask the folks who build sand sculptures:

http://www.harrisand.org/team_champion_photos.htm

… then they say that water hold sand together. If to substitute water with some kind of glue then it becomes a phenomenal opportunity for horn construction. It will be heavy, cheap, easily made by anyone, superbly damped, have necessary-rough surface. Just made the horn let the glue to solidify, cover the horn with some kind epoxy finish to protect the surface and the … fenita la comedia… The metal frames might be injected into the sand molds easily…

Other uses for polymer concrete have spun out of its use for counter tops, which can be large enough that cracking becomes an issue.  Hearths, sinks and even Roman style tubs have been constructed of this material.  Variations in the aggregates, reinforcements and polymers have resulted in a fairly stable material that might also be used for speaker enclosues, and mold shapes keep getting more elaborate. There is no doubt that this stuff could be used for horns to good effect, and some aggregates treated right might yield surfaces that required mimimal further finishing.  At the same time, it is possible to build up this material, so fine tuning - in the + direction at least - would likely be pretty easy.  Grinding it is possible, too, but not so simple.  Shrinkage of modern polymer concrete is minimal to negligible.  Lightweight aggregates are also in widespread use, along with ground glass and other materials chosen to enhance finished appearance.

Best regards,
Paul S

Romy the Cat wrote:

... a trip to a beach….

Everyone seems to be forgetting the difficult part of making any horn from a casting. It called a "mold". Making the mold is very time and labor consuming. Every time you want a different size, shape or flare rate you must build another mold. True, once the mold is made it is easier to cast a horn than machine one, but molds don't last forever either. If it was easy, then everyone else would be doing it.

Rgs, JLH

jessie.dazzle wrote:

I'd probably quit my day job if …. The much rumored new/old Vitavox drivers turn out to be good and available.

decoud wrote:

Yes, I should have said modular like your bass horns, but with much smaller segments, e.g. 36 segments of 10 degrees. Assuming one keeps the profile the same, the only difference between different sized horns is scale, so a single mould "capped" at variable lengths could be used to make a large range of horns. But I suppose it would not work if, like in your case, one needed to change the profile to suit other imperatives. (Though at 40Hz presumably one would have to start thinking about changing the house....)

Not to be pessimistic, but I have already visited this idea and it does not work. The problem with trying to “scale” sectioned panels is the amount of curvature in the panel sets the flare rate. Therefore, the flare rate is not “scalable”. The only way to change the flare rate is to change the number of sections. This in turn will change the angle of the mating surfaces along the edge. This then in turn requires a different mold for each flare rate. It is a no win situation.

Rgs, JLH

I have no comments about it besides assuring that the company that state all of it does crap in term of Sound. Still, I find that the way in which they think about construction of the walls of their back-loaded horn worth very much attention. Take a look:  

(Free-Press-Release.com) June 23, 2009 -- Many commercially available loudspeakers are closed-box enclosures and bass-reflex enclosures. Reasonably-priced backloaded horn speakers are not many because of internal complicated structure. So, many audio nuts made that by oneself. However, Hasehiro Audio achieved a low price. Moreover, they succeeded to eliminate right-angled bend. (i.e., elimination of a hollow-gray sound)  You can get yearning exponential backloaded horn speakers at last. Let's be intoxicated by a beautiful curve makes authentic backloaded horn sound.

1. The First Concrete Horn By Mr.Imanari:
- In about 1975, Mr.Imanari (Audio nut and director of invention school) introduced own invention at the floor.
- That's the first concrete backloaded horn speaker. - cubed concrete, 10cm unit and 2.5m long backloaded horn.
- Hasehiro requested the production to Mr.Imanari momentarily.
- After that, he got some orders by mouth-to-mouth advertising.
- But they take up to over 1 year from ordering to reception because he was hung up on new invention.
- As a result, it went of mind of audio nuts by little and little.

2. Batonpassing:
- In about 3 years after completion the first concrete backloaded horn speaker, Hasehiro thought - this is so wasteful that it has a tremendous amount of potential and anyone think of nothing to concrete backloaded horn and the making. - Hasehiro told his long-held aspiration to Mr.Imanari and he made a promise the tool passing and initiation of the technical know-how.
- But before that, Mr.Imanari was taken with illness and passed away after several months in a hospital.
- His heart swelled with put that out into the market for answer to the will of Mr.Imanari.
- Hasehiro told the antemortem promise to the bereaved family, and he received some undisposed tools from them.
- Hasehiro made trial model over and over imagining the making process from the tools.

3. Study From Fabric:
- Concrete characteristic vibration harden the tone color.
- So first, Hasehiro was starting to amelioration of concrete fabric.
- He changed black cement to white cement and also he changed aggregate and mixed in particular absorb sound chips.
- As a result, Hasehiro succeeded to remove concrete-specific sound character and could get the fabric know-how.

4. Pronouncement:
- In 1990, Hasehiro Audio submitted the model "AX" (discontinued) used 12cm unit to The International Housewares Show.
- After that, Hasehiro Audio submitted the succession model "HoPe-twoBx" (discontinued) used 16cm unit to the exhibition and they receive orders from after too.

5. Challenge To Double-Layered Structure:
- Hasehiro had wondered for a long time making the upper grade model used 20cm unit.
- But it looks about 50kg from specific gravity of concrete.
- So, it is difficult to distribute and had to give up.
- However, one audio nut suggested the double-layered structure of wood and concrete for not only weight saving but also think it should be a natural sound more add to wood sounding.
- Hasehiro had a lot of trouble. - cracks in the concrete when drying etc.
- But Hasehiro could resolve that for technical guidance from Onoda Cement Co., Ltd.
- In 1997, completed the world's first backroad double-layered horn speaker. - WCW-200A (discontinued)

6. Wood with Concrete Horn:
- That's a fusion with Japanese cement technology.
- WCW series is the backloaded horn speakers of double-layered structure. - implant concrete horn directly into wooden enclosure.
- WCW series reproduces unbelievingly clear and realistic sound. - controls resonance by wonderful integration of wood and concrete.
- Concrete horn of high radiation efficiency. - profound low tone and margin of high efficiency.
- That's not mere loudspeakers anymore.
- That's the exact live reappearance equipments.
- WCW series gold titled in eliminate tube amp category of The Vacuum Tube Audio Fair in Akihabara from 1998 to 2000, 2002 and 2003 (From 2004, no elimination races)

That's "Hasehiro Premium"

decoud wrote:

One of the problems with horns is the inflexibility of frequency cut-off: you are limited to a discrete number equal to the number of horns you have. This makes experimentation difficult without having an absurdly large array of different horn sizes to try. So how about the following configuration: The entire loudspeaker is a single profile that changes continuously in cross section from floor to ceiling with high frequencies being in the centre and low at the extremes. Any cut-off frequency is therefore always available (in two positions): it is simply a matter of driver positioning. Equally, the only limit on the number of "horns" is the number of drivers. Removable horizontal septations can be introduced if necessary but it would be nice to do without them. Once the optimal profile is determined the thing would be trivial to build: it could be just a series of CNC'd slabs of mdf stacked on top of each other. Rgds, d

What you have there is Tom Danley's Unity Summation device in principle. Tom has a predictable method that limits the trial and error approach. It would be very difficult to get the frequency response flat for your example. The distance between the drivers is too great and will result in a lot of phase and timing problems.