Jean Michel on LeCleac'h horns - Page 93 - diyAudio
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Old 14th January 2011, 08:40 AM   #921
Jmmlc is offline Jmmlc  France
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Hello revintage,

Because we are less sensitive to phase distorsion at low frequency, the rule to use an electrical cut-off frequency for the high pass crossover one octave above the acoustical cut-off of the horn can be overpassed.

So you can use a lower cut off than 400Hz for a 200Hz horn .

Best regards rom Paris, France

Jean-Michel Le Cléac'h


Quote:
Originally Posted by revintage View Post
Could we suppose that the cutoff-frequency, in ballpark figures, can be twice the design-frequency?
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Old 14th January 2011, 08:46 AM   #922
Jmmlc is offline Jmmlc  France
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Hello,

In his white paper about directivity
http://www.gedlee.com/downloads/directivity.pdf
(A white paper by Dr. Earl Geddes, GedLee LLC )

Earl Geddes defines on page 9 what is the "optimum" frequency response curves (shown at 0°, 15°, 30° 45° and 60°) for a sterophonic listening in order that the frequency response remain constant in a "listener plane" (3 listening positions called A, B and C are shown in that plane)

The optimum frequency curves as defined by Earl Geddes are shown on figure 11 of the document.

Also on figure 10 an achievable "optimum" polar map is shown (showing that a slightly increasing directivty with frequency is desireable).

From the measurements made by Jack Zagaja on the E-JMLC-1000 horn I could retrieve the frequency curves at 15°, 30° 45° and 60° after the 0° response is flatten.

You can see on the attached graph, the comparison between the frequency response curves obtained on the E-JMLC-1000 horn and the "optimum" frequency response curves defined by Earl Geddes.

The fit is very good specially between 2.5kHz and 7kHz.

The EOS waveguide, due to the (3dB) hole between 3kHz and 6kHz
http://2.bp.blogspot.com/_vk3bkhlDpP...0/summa_FR.jpg
doesn't reach that result.

Can we conclude that the E-JMLC horn meet both the requirements of the best horns in matter of loading and smoothness of the response curves an an excellent directivity control as the best waveguides?


Best regards from Paris, France

Jean-Michel Le Cléac'h
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File Type: gif e_jmlc_1000_dir.gif (26.8 KB, 819 views)
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Old 14th January 2011, 12:37 PM   #923
Fuling is offline Fuling  Sweden
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Two layers of white gelcoat before before the fibreglass and resin took away some of the negative WAF
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File Type: jpg lecleach 009.jpg (71.3 KB, 803 views)
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Old 14th January 2011, 01:17 PM   #924
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Default To what extent?

Quote:
Originally Posted by Jmmlc View Post
Hello revintage,

Because we are less sensitive to phase distorsion at low frequency, the rule to use an electrical cut-off frequency for the high pass crossover one octave above the acoustical cut-off of the horn can be overpassed.

So you can use a lower cut off than 400Hz for a 200Hz horn .

Best regards rom Paris, France

Jean-Michel Le Cléac'h

Specific conditions for a compression driver, assuming displacement limit, [Fs] and horn length are not at issue:

[n] Octave above ([F3] = [n]*2*[Fc]): 1 3/4 1/2 1/4
...................................HP filter slope:.?...?.....?.....?


Regards,

WHG

Last edited by whgeiger; 14th January 2011 at 01:21 PM. Reason: Layout
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Old 14th January 2011, 01:21 PM   #925
soongsc is offline soongsc  Taiwan
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Quote:
Originally Posted by Jmmlc View Post
Hello,

In his white paper about directivity
http://www.gedlee.com/downloads/directivity.pdf
(A white paper by Dr. Earl Geddes, GedLee LLC )

Earl Geddes defines on page 9 what is the "optimum" frequency response curves (shown at 0°, 15°, 30° 45° and 60°) for a sterophonic listening in order that the frequency response remain constant in a "listener plane" (3 listening positions called A, B and C are shown in that plane)

The optimum frequency curves as defined by Earl Geddes are shown on figure 11 of the document.

Also on figure 10 an achievable "optimum" polar map is shown (showing that a slightly increasing directivty with frequency is desireable).

From the measurements made by Jack Zagaja on the E-JMLC-1000 horn I could retrieve the frequency curves at 15°, 30° 45° and 60° after the 0° response is flatten.

You can see on the attached graph, the comparison between the frequency response curves obtained on the E-JMLC-1000 horn and the "optimum" frequency response curves defined by Earl Geddes.

The fit is very good specially between 2.5kHz and 7kHz.

The EOS waveguide, due to the (3dB) hole between 3kHz and 6kHz
http://2.bp.blogspot.com/_vk3bkhlDpP...0/summa_FR.jpg
doesn't reach that result.

Can we conclude that the E-JMLC horn meet both the requirements of the best horns in matter of loading and smoothness of the response curves an an excellent directivity control as the best waveguides?


Best regards from Paris, France

Jean-Michel Le Cléac'h
I've read another paper that has a different point of view as calculated based in Interaural Time difference and Interaural Intensity Difference. So I wonder how the referenced paper here defines the ideal directivity.
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Old 14th January 2011, 01:54 PM   #926
Jmmlc is offline Jmmlc  France
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Hello WH Heiger,

I consider the user of my recommandation sufficiently clever as to do the best choice in order that the phase distortion of the whole group delay curve will be sufficiently unaffected by the rise of the group delay of the horn near its acoustic cut-off.

But a 3rd order Butterworth high-pass filter the f-3dB of which is set one octave above Fc will do the job.

Best regards from Paris, France

Jean-Michel Le Cléac'h

Quote:
Originally Posted by whgeiger View Post
Specific conditions for a compression driver, assuming displacement limit, [Fs] and horn length are not at issue:

[n] Octave above ([F3] = [n]*2*[Fc]): 1 3/4 1/2 1/4
...................................HP filter slope:.?...?.....?.....?


Regards,

WHG
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Old 14th January 2011, 09:17 PM   #927
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Default FWIW

JMLC,
The question I asked was for the benefit of other readers, myself included.
For the example cited, [n]=1 & [m]=18 db/Oct, there is no "overpass".
Typically, [n]=3/4, [m]=12 dB/Oct is the lower bound.
Is this later example what you mean by "overpass"
What is the experience with your horns regarding the setting of min[F3]?
Regards,
WHG
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Old 17th January 2011, 03:27 PM   #928
Jmmlc is offline Jmmlc  France
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Hello

Jack Zagaja used to show the directity sonogram of the E-JMLC-1000
http://www.diyaudio.com/forums/attac...8_sonogram.gif


It is interesting to compare that result to the directivity sonograms published on that site:

Red Spade Audio: Waveguide shootout

Best regards from Paris, France

Jean-Michel Le Cléac'h





http://www.diyaudio.com/forums/attac...8_sonogram.gif
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Old 18th January 2011, 08:04 PM   #929
jzagaja is offline jzagaja  Poland
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Article shows directivity sonograms normalized to 0 deg where there will be always narrowing of directivity because of WG resonances and mouth diffraction. Better normalize to arbitrary angle or power response. Otherwise non axi-symmetrical WGs will always "look" better. Michael's Minphase horn seems the smoothest.
Attached Images
File Type: gif OSWG_norm.gif (20.7 KB, 647 views)
File Type: png Minphase.png (50.9 KB, 637 views)
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Last edited by jzagaja; 18th January 2011 at 08:06 PM.
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Old 19th January 2011, 01:20 AM   #930
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Default Hype!

Quote:
Originally Posted by soongsc View Post
I've read another paper that has a different point of view as calculated based in Interaural Time difference and Interaural Intensity Difference. So I wonder how the referenced paper here defines the ideal directivity.

The following closing remarks clearly demonstarte the mission of this "white paper":

"Basically no loudspeaker which does not use a waveguide is going to be able to match the Summas performance. Piston source loudspeakers simply cannot do what a waveguide does. But all waveguides are not equal either. The Summa has a particularly high directivity, which is desirable in a small room (another topic altogether)."

Regards,

WHG
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