Coral Flat 5 Series II in Fostex FE108e∑ Back Loaded Horns….,

Hi all, Can I hear of the view of you fine experts on whether Coral Flat 5s would work in Fostex FE108ez horns. The drivers are 132mm wide yet the horns designed for 108mm wide drivers. With the Corals being a 5-inch driver, there are limited horn designs, plus I’d love to build the above design, but I need to get advice as it’s a lot of effort and money to get wrong.

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The Fostex horn has such a small mouth area that it really just work as a quarter wave resonator below 100 Hz, so why not use a well designed voigt pipe like the frugal horn.
If you really want to build a horn something like a 5/8 scale of "the big fun horn" or "Schmacks horn", might work, with their far larger mouth areas
Dear Planet 10,
The Voigt is a quarter wave resonator with a I: positive flare II: the driver situated close to 1/3 from the closed end III: A constriction at the open end.
So I assumed that the Frugal is also a quarter wave resonator with positive flare, offset driver and constriction is in that family. However, if you as a constructor want to split the Frugal in a different more strictly defined group, I fully respect that.(y)
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It is more complex than that. Can’t remeber exactly, but something like a paraflex, with a choke (borrowed), and a termination that might defy description. Shows how someone who knows what they are doing (Scott) can do using powerful tools (MJK+more).

We struggled for years trying to come up with something to succeed Frugel-Horn (Mk1). Many, many stabs before a reved driver inspired him. Got a design on Sun, Chris delivered on Wed. It did not work. Reved design the next day, Chris delivered second prototypes Saturday. Scott knocked it out of the park. Frugel-Horn Mk3 was born. Mk2 was stillborn.

It is more complex than that.
It certainly is, but on the other hand it is also a straightish pipe with a constricted end.

I sometimes feel that the fullrange driver people kind of go in circles. If someone calls a straightish pipe a horn, we haste to say it acts more like a TL, if someone says its mostly a TL or like a Voigt, we point out that it's as much a horn because of positive taper etc.

I studied evolutionary biology and my field of specialization was taxonomy, groupings of species into a structure that reflects their evolutionary relationships. And in that field you have "lumpers" and "splitters" which are people that make few large groups based on similarities (lumpers) and ones that make many small groups based on differences. They both have merits, they need to know/understand eachother's positions.

That's the cause of my little giggle.

That said, I have repeatedly recreated FH3 in hornresp to learn from it. It definitely expanded my tricks for designing similar enclosures. I have not tried out different flares for the two sections of the pipe, but it's high on my list of priorities.
As a minor tip -it's partly on 3d expansion assumptions so plane-wave gets you a goodly way, but not quite everything.

I try not to get too involved with names. With the technical hat on, FH3 is a [single] tapped* parabolic corner pipe-horn with an internal low-pass expansion choke. Which isn't much of a name, so these days I usually just call it a tapped corner horn. It's a nominal hypex, but having parallel sides strictly speaking shifts it into the parabolic. A [single] tapped horn is arguably another way of saying 'Voigt horn', aka 'pipe horn' -but not necessarily the same thing as a 'Voigt pipe', which in its most common form (e.g. the LCON VP variation shown) technically makes the definition because it's a pipe with positive expansion to the terminus, but isn't really designed the same way since its a pure standing-wave generator in its passband, whereas something like FH3 & some other types actually have sufficient expansion for horn loading.

Voigt is a bit of an odd one really, since if you go back to his original '34 patent application, he never really made much in the way of specific stipulations. He noted in one implementation [up to] a potential 2.5:1 expansion & in essence a 1/2 tap location for certain organ-pipe derivations, but the majority, including the expanding pipes, were end-loaded or nearly so. Same went for his famous corner horn -end loaded. All the expanding pipes were truncated, with the arguable exception of the organ pipe which was slightly more complicated in the details of the cross section & the slightly offset small vent, though he didn't provide any details and since all he really said about the sketch was how the driver 'might be mounted' I suspect he never actually tried it -or hadn't at that time. I've never got to the bottom of where the typical 'Voigt pipe' (e.g. the attached) ever really came from; I always assumed it was developed empirically from a handful of ROTs that had developed over the years, partly from slightly erroneous interpretations of Voigt's patent, partly from trad. BR design, and partly from -your guess is as good as mine & probably better. ;)

*as distinguished from Tom Danley's or the Jensen Transflex sub., which are technically double-tapped since the driver excites the enclosure at two distinct points in its expansion.


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I got my Ph. D. in clinical microbiology a long time ago, so I have also tangled with taxonomy. Then DNA sequencing came and reshuffled the cards again! For me a "pipe" is a loudspeaker that use resonances related to the length of the pipe. A "horn" use a positive flare leading up to mouth with large enough area to increase radiation resistance over a wide frequency range.

So for the klipsch corner horn the "horn" part dominate for the Fostex horn above of about equal length the "pipe" will dominate over the "horn".
They all exist in a continous spectrum so the borders between horns and pipes are not clear cut.
Now that I'd mostly agree with. While any pipe with positive expansion to the terminus is technically a horn, whether it actually gets any loading over its effective / operating BW is another matter -restrict expansion sufficiently and from a functional POV it's a standing wave generator, albeit one operating over a relatively broad BW thanks to the expanding profile, how much depending on the design. The Fostex box above is one of their better offerings (all three ESigma designs were) in that sense with a reasonably balanced gain characteristic for the design intent, though realistically they only provided any horn loading / impedance matching at the very top of their operating range (and that was mostly the larger 208 design for obvious reasons).
Hi Seagull,

The Coral Flat 5 were very nice drivers once and still are, IF they are still in good state. Many of those old FR drivers with light paper cones and light suspensions suffer from problems nowadays. But IF you have a nice and equal pair, they´re worth the efforts to make a nice "box" for them.
How to be sure? Measure impedance, calculate TSP, measure response and distorsion. Then you have a base for simulating behaviour in different types of enclosures, all else is guesswork, sorry.

All the best