# Jean Michel on LeCleac'h horns

#### angeloitacare

hello Jean Michel

Angelo

#### Pano

Paid Member
I'll start!

Perhaps Jean Michel would like to explain something about his horn profile. What was the begining design idea?

How is it different from other profiles such as:
Conical
Exponential
Hyperbolic
Tractrix
Iwata

What advantages does the LeCleach'h horn have over any of these?

A vous, Jean Michel!

.

.

(I have heard and/or built all of the above, but have not heard the LeCleac'h)

#### tinitus

Tried to calculate fore a 10" midbass going down to 150-200hz
I want it to be about 350mm hight and about a meter wide

But the calculation shows a length og around 850mm, which is fine, but suggests a mouth width of 10 meter

#### tinitus

Ahh, I reckon I should just look at the area at a shorter length
This is exciting

#### Attachments

• midbass horn.jpg
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#### Jmmlc

Hello Panomaniac,

While it has been eventually said that the Le Cléac'h is based on Webster's equation, in fact the expansion law is secondary when considering the horn known as Le Cléac'h horn since David Mc Bean used to introduce this profile into Hornresp and since Bjørn Kolbrek call it that way in the second part of his paper in Audioxpress

part 1 :

part 2:

In fact my contribution should be looked more as a method to calculate horns than rather a new expansion.
If one of those days Angelo should invent a new expansion law for a horn then my method could be applied to calculate it's profile.

If we start from a given expansion law for the evolution of the area of the wavefronts versus their distance, by example catenoidal or hypex or exponential, what is the difference between my method and the anterior methods?

For commodity I prefer to define the wavefront as an equiphase surface described by the ensemble of points reached at the same time by a single wave emitted at the throat.

All anterior methods rely on an hypothesis for the shape of the wavefronts. Common and false hypothesis taken for the calculation of horns is that the wavefronts are planar. Voigt took for his Tractrix horn the hypothesis of spherical cap wavefronts having a fixed radius. Kugelwellen horns are based on the same hypothesis but with a doubled radius compared to the Tractrix.

During the 70's and the beginning of the 80's I was looking at the rare published pressure fields maps inside horns ( measurements by Morse in Mac Lachlan's book, by Hitachi Labs in Jean Hiraga's book, ... ). This readings lead me to think that all the anterior methods to calculate horns were eroneous as the mesured wavefronts where neither planar neither spherical.

I had the idea that if a single wave was propagating in the case the speed of sound was constant inside the horn, the above mentioned equiphase surfaces should be parallel ( = orthogonally equidistant ) each one from the other, a feature than you don't find, by example, in Voigt's hypothesis for the design of the tractrix horn for which the wavefronts cannot be orthogonaly equidistant (because they are translated at constant “speed” along a common direction). Another requirement is that the wavefronts should reach the walls of the horn at 90°.

At the time I used to program a first profile in Basic on one of the first computer I had in my lab (a Hewlet Packard 9625 if I correctly remind). I used for that a method based on more than 1 million of discrete geometrical elements the assembly of which possess the required parallelism I was looking for. No hypothesis was done on the shape of the wavefronts, the only hypothesis was their equidistance (and a known expansion law...).
It is only after personnal computers were available that I wanted to wrote a first QuattroPro spreadsheet and many years after an Excel spreadsheet... I built the first horn using that method in 1982.

Fortunately I could replace the calculation of millions of discrete elements of the original software written in Basic into a recursive formula. Around 1995 that horn was discussed on Joenet (Sound Practices ‘s discussion list) and on the french speaking group [son-qc] and I was asked to commit a paper which one was published in issue N°6 of “Musique & Technique” a publication of the Belgian Lowther Club. In 1998 Marco Henry (Musique Concrete) used to read that paper and some time later he begun to build in France his Jerzual horns calculated by my method . Nearly at the same time, Martin Seddon in Australia begun building a large format Le Cléac’h horn (now known under reference Azura Horn AH160) and the first batch came in USA where the horn received good fame within the horns/tubes crowd. One of the first user was famous tube electronics builder Dave Slagle ( see http://www.arduman.com/aa/Sayfalar/slagle/slagle.htm )

One thing that schocked many persons when they first saw the profile calculated by this method for an hypex or an exponential horn was the rolled back mouth. Even, many people were convinced at this time that the rolled back mouth was an empirical choice I made. The truth is that it is fully “natural” and results from the combined parallelism and expansion law. Unfortunately today many persons still think (wrongly) that is is useless to curve back the mouth and that the horn can be stopped when the opening angle reaches 180°.

Another question that was often asked was why the horn is wider than all commercial horns having the same acoustical cut-off. It is because in order to reduce at maxium the reflection of waves from mouth to throat we need to open the horn at more than 180° (I recommand 360°). Doing this we can consider the horn as quasi-infinite (measurements confirmed the simulations done with that hypothesis).

There was several versions of the spreadsheet, the first ones rely on the simplified hypothesis that the curved width of a given wavefront could be estimated from the diameter of a disk having the calculated area. The last versions use a step by step estimation and are much more precise, specially near the mouth.

Best regards from Paris, France

Jean-Michel Le Cléac'h

panomaniac said:
I'll start!

Perhaps Jean Michel would like to explain something about his horn profile. What was the begining design idea?

How is it different from other profiles such as:
Conical
Exponential
Hyperbolic
Tractrix
Iwata

What advantages does the LeCleach'h horn have over any of these?

A vous, Jean Michel!

.

.

(I have heard and/or built all of the above, but have not heard the LeCleac'h)

#### tinitus

Hi Jean Michel

I understand what you say about mouth curves, that they should prolong all the way, and not stop at 180gr

But surely you cant demand that at low frequencies, where we are bound to make compromises

Is there a frequency where it gets important or where its less important

Im mostly thinking of 150-1khz

edit,
I have been trying to find your previously posted layout of an idialised elliptical horn, but cant find it

#### angeloitacare

If one of those days Angelo should invent a new expansion law for a horn then my method could be applied to calculate it's profile.

ha ha, i think that would be a little over my mind and abilities....

but, a curiosity of mine, and i guess, never asked you , Jean Michel :

I guess you experimented over the years a series of drivers : which ones do performe best in your opinion with your horns :

- in the mid-bass region ( 200hz - 1000hz )
- in the midrange region ( 1000hz - 10khz )

if i remember right, you mentioned you use Yamaha drivers. What is your opinion abouth them ? i can get a pair with 1" exit, and 3" aluminium diaphragm. Suspention seems to be the same as from the JA 6681B. Do you think these are worth a try, and a contender with S2 ?

Angelo

---------------------------------------------------------
http://www.audiovoice-acoustics.com/forum/

#### soongsc

Jean-Michel
If I want the initial angle to be a certain angle, how can I do that?

#### Jmmlc

Hello Angelo,

The best sounding low mid compression drivers I used to listen were:

1) Goto
2) WE555 (I have the Alnico French modification by LMT)
2) Onken
3) Yamaha JA6681 (I have 2 pairs of them)
4) TAD TD2001 (yes, a bit modified and on the Sato horn above 250Hz)
5) Vitavox S2
6) Philips

The best sounding mid compression drivers I used to listen were:

1) Onken
2) TAD TD2001 (I have 3 pairs of them with old or recent diaphragms)
3) Goto
4) Altec 288

Best regards from Paris, France

Jean-Michel Le Cléac'h

angeloitacare said:

ha ha, i think that would be a little over my mind and abilities....

but, a curiosity of mine, and i guess, never asked you , Jean Michel :

I guess you experimented over the years a series of drivers : which ones do performe best in your opinion with your horns :

- in the mid-bass region ( 200hz - 1000hz )
- in the midrange region ( 1000hz - 10khz )

if i remember right, you mentioned you use Yamaha drivers. What is your opinion abouth them ? i can get a pair with 1" exit, and 3" aluminium diaphragm. Suspention seems to be the same as from the JA 6681B. Do you think these are worth a try, and a contender with S2 ?

Angelo

---------------------------------------------------------
http://www.audiovoice-acoustics.com/forum/

#### Jmmlc

Hello Soongsc,

In the version you have of the spreadsheet the tangential angle of the wall of the horn is imposed by the evolution of the area with the distance to throat (resulting from your choice of throat diameter, T coefficient and Fc).

For an arbitrary set of those 3 parameters the angle at throat is fixed. You have two solutions to obtain the angle you want:

1) try different values of the diameter, T coefficient and Fc until you reach the desired angle

2) calculate a spline curve that will progressively go from the tangential angle you desire to a given Le Cléac'h horn profile.

(the angle value you can enter in the actual spreadsheet will have some effect on the profile only if the angle of the throat of the driver is quite near of the throat angle of the horn)

Best regards from Paris, France

Jean-Michel Le Cléac'h

soongsc said:
Jean-Michel
If I want the initial angle to be a certain angle, how can I do that?

#### Jmmlc

Hello Tinitus,

I know thar some difference exists between my recommendations and what people do with those.

You'll see on the pictures on the page:
http://www.melaudia.net/rueil0903.php
what I consider as the maximum width for an axial Le Cléac'h horn.
We'll have a public demo of that horn during the weekend of 28 & 29 (march 2009).

For cut-off frequency under 150Hz I don't recommand the complete axial horn calculated by my method.
I recommand a quarter of axial horn placed on a corner of the listening room as on the picture:
http://ndaviden.club.fr/pavillon/axial_murs.gif

For very low cut-off frequency I recommand 2 halves of quasi-cylindrical waves Le Cléac'h horns
http://ndaviden.club.fr/pavillon/cyl_mur.gif

You can see a picture of such a realisation at:
http://img383.imageshack.us/my.php?image=dsc30511280x768ac0.jpg

Best regards from Paris, France

Jean-Michel Le Cléac'h

tinitus said:
Hi Jean Michel

I understand what you say about mouth curves, that they should prolong all the way, and not stop at 180gr

But surely you cant demand that at low frequencies, where we are bound to make compromises

Is there a frequency where it gets important or where its less important

Im mostly thinking of 150-1khz

edit,
I have been trying to find your previously posted layout of an idialised elliptical horn, but cant find it

#### soongsc

Hello Jean-Michel,

Is there no relationship between T and the initial angle? Is there a geometrical deffinition in relation with T?

#### Jmmlc

Hello Soongsc,

T is a coefficient in the general frouma linking the area and the distance to throat for horns of the hyperbolic family

http://www.bd-design.nl/contents/media/hypo.gif

T = 0 : catenoidal horn
T between 0.5 a,d 0.707 : hypex horn
T = 1 : exponential horn
T infinite for conical horn.

Best regards from Paris, France

Jean-Michel Le Cléac'h

soongsc said:
Hello Jean-Michel,

Is there no relationship between T and the initial angle? Is there a geometrical deffinition in relation with T?

#### Pano

Paid Member
Jmmlc said:
In fact my contribution should be looked more as a method to calculate horns than rather a new expansion.

All anterior methods rely on an hypothesis for the shape of the wavefronts.

Ah! D'accord! Now I understand. Sometimes it just needs to be spelled out in plain langauge. =)
Thanks so much for that - it really helps understand what you are doing. Very interesting information in your post.

Thanks to Angelo for starting the thread.

#### tinitus

Jean-Michel
Fantastic "feedback"
Very informative

Thank you

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• lecleach midhorn.jpg
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• hjørnehorn.jpg
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#### pk

Hi Jmmlc,

I have a question regarding the system that according to your post above will be demonstrated ultimo March:

http://www.melaudia.net/rueil0903.php

Could you please specify the crossover points of this system?

Thanks!

Best regards
Peter

#### tinitus

floor placement? or floor/wall?

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Or maybe more like this one

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• stort bashorn.jpg
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#### tinitus

I know this is approved

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• floor horn.jpg
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