Omni-directional Horn-speaker 2426H

[MattiasAs]

Hello,

I need advice or (mathematical) helps.

I want to build a omni directional horn. I want to use the JBL 2426H driver in combination with JBL 2118H. Crossover frequence about 800hz
How can i calculate the horn for the 2426H and the 2118H?
Do you think its an good idea?

Kind regards Matthias

[ivica]

Hello,

I need advice or (mathematical) helps.

I want to build a omni directional horn. I want to use the JBL 2426H driver in combination with JBL 2118H. Crossover frequence about 800hz
How can i calculate the horn for the 2426H and the 2118H?
Do you think its an good idea?

Kind regards Matthias

Hi Matthias,
1.
https://www.grc.com/acoustics/an-introduction-to-horn-theory.pdf

2.
http://www.audioxpress.com/assets/upload/files/kolbrek2885.pdf

3.
https://pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Kolbrek_Bjorn/Intro_Horn_Theory.pdf


So when decide the type of the horn You want to make, You an recalculate step by step (say every 2mm apart) the sound wave front surface area depending of the distance from the horn throat, and to start wood milling . I wish You great success in Your work.

regards
ivica

[Val]

Hi Matthais,

I too have been thinking about applying the 2425/2426 to the Bella Luna Diamante design. Have you had a chance to hear one? I've not found one locally to listen to here in California.

I own 2425/E110/E155 that are available for a DIY project and I am considering this design too (though the E155 needs a 3.1 cu ft cabinet). These drivers are from a pair of 4699b's I have: http://www.audioheritage.org/vbulletin/showthread.php?34431-What-to-do-with-my-4699b

Do post any progress you make!

79771

[Jan Daugaard]

I have helped make 3D drawings of the Bella Luna horn, and I am confident that Matthias will succeed in milling such horns.

[ivica]

I have helped make 3D drawings of the Bella Luna horn, and I am sure that Matthias will succeed in milling such horns.

Hi Jan Daugaard,

Nice looking design.
What type of horn surface cross-section has been applied in the calculation?
I wonder where such 'omni-directional horn speaker' can be applied ?

reagrads
ivica

[Jan Daugaard]

This is a 184.54 mm long exponential horn with a 104.16 times expansion (from 506.71 mm² to 52778.76 mm²).

We need a transition from vertical to horizontal, and I decided upon a quarter ellipse (the red curve). The remainder of the horn is straight (the blue curve).

I wrote a C++ programme to bend the horn around a curve like this one (the red curve followed by the blue curve) and to generate a point cloud for conversion into a 3D drawing. The conversion of the point cloud was carried out by CATIA (https://en.wikipedia.org/wiki/CATIA).

This is how the length of the horn to a given point on the red curve is calculated:
https://en.wikipedia.org/wiki/Elliptic_integral#Incomplete_elliptic_integral_of_ the_second_kind

The bending programme also requires the normal line
https://en.wikipedia.org/wiki/Normal_(geometry)
to be calculated for any given point on the curve.

The woofer is radiating into a surface given by a quadratic function such that the slope is 1 at the centre and 0 at the outer edge.

The benefit of this design is that the loudspeaker comes close to being a point source horizontally.

[Horn Fanatic]

Hello,

I need advice or (mathematical) helps.

I want to build a omni directional horn. I want to use the JBL 2426H driver in combination with JBL 2118H. Crossover frequence about 800hz
How can i calculate the horn for the 2426H and the 2118H?
Do you think its an good idea?

Kind regards Matthias

Greetings -

A standard factor in horn design, is the crossover point should be one octave above the horn low frequency cut off. For example, the ALTEC Lansing 811 horn has an approximate 400 cycle flare rate. The circumference of a standard Exponential horn, be it round or square, will be the wavelength at the horn low frequency cut off. Your horn in question appears to be a possible Hyperbolic flare. I prefer the Hyperbolic equation over the standard Exponential equation, because a certain variable allows for finer dimensional adjustment of the horn mouth area, while maintaining the prescribed horn length, initial cross section to a fashion, and throat area. This is especially handy when designing low frequency horns for domestic applications.

There is however, a limit to fudging the mouth area, that by decreasing a certain variable too much can result in ending up with a Catenoidal horn. Get ready for some awful distortion. Standing waves as a result of propagating a low frequency wave down a small mouthed, flared tube. Having the crossover frequency an octave above the horn low frequency cut off will preclude any chance of horn mouth reflections of waves back to their origin.

Horn mouth reflections are caused when the wavelength of the lowest frequency to be transmitted, is at, or near the circumference of the horn mouth. A good example of wave reflection will be why microwaves in an oven to do penetrate the screen in the window. The wavelength of the approximate 2 Gigahertz frequency is at, or greater than the circumference of a single hole in the screen. The wave bounces back into the oven, thereby not cooking your eyeballs.

I will refer you to Vincent Salmon, who developed and published his equation in 1946. The Jensen Company I believe, was the first company to commercialize his work. The Hyperbolic equation may appear intimidating, but it is quite simple. I wrote a spread sheet 30 years ago that works out great. If you cannot find the Salmon paper, you will find the equation in the book, 'Acoustics' by Leo Beranek. Understandably, in the chapter on horns.

Your horn is technically, folded. Tannoy adopted that concept with their TP 1 corner cabinet back in the late 50's.

Learning the math will allow you to design smaller or larger horns of the type you're interested in. I will point out, that when you fold, or bend a horn, you must maintain the proper cross section along it's length around the bend. If you can find someone to model a horn from your calculations, you may have them create a file to facilitate the two parts being carved on a CNC machine.


Good luck,

HF

[Val]

Following this thread with interest and appreciating the posts!