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Old 17th January 2009, 03:31 PM   #1
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Default Tractrix

I'm looking into building a BLH Styled like the little big horn form Carfrae !! I think it is a Tractrix flared horn and they use Lowther DX 4 . is there any software that would help calculating tractrix horn and the volume needed in the chamber behind the driver and area of throat and mouth . Did anybody attempt such a project ? are there clones ? with cheaper drivers like fostex ?
JP
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Old 17th January 2009, 04:14 PM   #2
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FWIW, Tractrix is a generally poor choice for a BLH due to needing to be excessively large to go low with any authority. A T (M) = ~0.7 is a good compromise between size, gain BW same as a FLH. Regardless, either can be designed in Hornresp or AkAbak, though the latter has a steep learning curve due to its much greater input flexibility, so best to get the basic design done in HR and export the data into AkAbak to fine tune it.

GM
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Old 17th January 2009, 04:21 PM   #3
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edit -you beat me to it Greg.

Tractrix isn't an ideal contour for bass horns -it'll work, but it needs to be substantially larger, and if you compromise a tractrix, what you end up with is an exponential horn anyway (I'm not much of a fan of those either if it comes to that).

There are numerous formulas for calculating the Vb of the low-pass chamber, so it's a case of pick & choose what you want. As for the throat, depends what it is you're trying to achieve.

Re software, as GM suggests, Hornresp is very good of the available programmes, plus, it's free, which is a bonus. So is AkABAK, but it's not for the faint-hearted, so if you haven't done this before, I suggest you avoid it.
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Old 17th January 2009, 04:22 PM   #4
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Ah, the white whale of speaker building. This is a start:

http://www.randteam.de/AkAbak/Index.html
http://www.aj-systems.de/indexe.htm
http://mywebsite.bigpond.com/dmcbean/

Ultimately, it needs to be scratched out with pencil and paper first. In no particular order you have to figure out:

1. An appropriate driver (i.e., low Q, big magnet, rising response)
2. Target LF cutoff (e.g. 50hz?)
2. The placement (corner? 8-fold mouth reduction. wall? 4-fold, etc.)
3. Values for length, mouth, throat, flare (pure math)
5. Integration of driver's response, baffle step, horn action and quarterwave/TL action (months of tearfully frustrating simming if you can even get software to sim all these)

I tried for months to unravel this and for my brain, there are too many variables and you have to be incredibly stubborn to really crack the design. Isn't it interesting that MJK created the model to sim one, but then never personally found one he wanted to build? Also, Ron conquered that territory and promptly moved to OB's -- what does this tell us? That it's a fascinating intellectual challenge and a learning experience like no other, but it's pure madness. (And obviously there's lots of fun to be had.)

Check out the Replikon, too -- at least you can view the ("non curvy") plans for that and could "rebuild" it in a curvy fashion. BLH's are a tough nut to crack, and you might take a shortcut by simply building one (a woodworking challenge), rather than designing one (math, physics, sims, a large set of variables...) Unless it's too late for you, Ishmael.
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Old 17th January 2009, 05:55 PM   #5
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Quote:
Originally posted by Scottmoose

.........what you end up with is an exponential horn anyway.......
Actually, do it right for a wide BW BLH and both wind up hyperbolic.

GM
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Old 17th January 2009, 07:01 PM   #6
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Quote:
Originally posted by rjbond3rd
Check out the Replikon, too
Replikon is a BVR like all the Spawn "Changs"

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Old 17th January 2009, 09:37 PM   #7
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Quote:
Originally posted by GM
Actually, do it right for a wide BW BLH and both wind up hyperbolic.
GM
True. And usually with an M of around 0.5, right?
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Old 17th January 2009, 09:59 PM   #8
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Right, in an ideal BLH it will hover around 0.5, but few are, mainly because the wrong driver is used for the app, so a 'good enough' performing alignment typically winds up around 0.7 - 1.0 (hypex-expo).

GM
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Old 18th January 2009, 12:45 AM   #9
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Originally posted by planet10 Replikon is a BVR like all the Spawn "Changs"
Hi Dave, yeah I just meant aesthetically, it's curvy like the Carfrae. The Replikon looks more like Bruce to me. I heard the Harveys today -- oh man, incredible.
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Old 18th January 2009, 01:37 AM   #10
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Originally posted by rjbond3rd
I heard the Harveys today -- oh man, incredible.
This was the event at Phil's? Tell us more.

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