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Old 24th March 2011, 03:29 PM   #431
jzagaja is offline jzagaja  Poland
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You can CNC adapter locally - spreadsheets are available.
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Old 24th March 2011, 03:33 PM   #432
Paul W is offline Paul W  United States
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Jack,
What measurement distance do you use? Distance to throat or mouth?
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Old 24th March 2011, 03:33 PM   #433
jzagaja is offline jzagaja  Poland
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Hottest projects in summer 2011: OB and WG for dipole RAAL 140-15d.
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File Type: jpg Autotech_OB.jpg (24.0 KB, 525 views)
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Old 24th March 2011, 03:36 PM   #434
jzagaja is offline jzagaja  Poland
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Quote:
Originally Posted by Paul W View Post
Jack,
What measurement distance do you use? Distance to throat or mouth?
From mouth 80-100cm (30-40 inches) when in room, BK4149 with 2610 amp.
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Old 24th March 2011, 04:10 PM   #435
badman is offline badman  United States
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Quote:
Originally Posted by jzagaja View Post
Hottest projects in summer 2011: OB and WG for dipole RAAL 140-15d.
I don't see the value in using the same size horn for the tweeter.....
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Old 24th March 2011, 06:09 PM   #436
JoshK is offline JoshK  Canada
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Quote:
Originally Posted by krzys View Post
Do I interpret it right? The Tractrix is the smoothest, the Miniphase is the less directional although not so smooth and the JMLC is very directional (beams)?
Chris

No I don't think that is right. Compare the -5db contours for both the tractrix and the JMLC and you will see that the tractrix has a much narrower beamwidth at higher freq than the JMLC, which is to say the tractrix beams more. Its rate of change of beamwidth is a little slower however, but its coverage is narrower.
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Old 24th March 2011, 06:30 PM   #437
krzys is offline krzys  Canada
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To joshK, this time I looked carefully. Both have about the same coverage up to 10 kHz then JMLC narrows quicker.
I then have another question: what does it mean that the JMLC has strong 2.5 dB contour and Tractrix don’t have it at all? different efficiency of the horns? JMLC would play louder on axis ?
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Old 27th March 2011, 12:46 PM   #438
jzagaja is offline jzagaja  Poland
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Tractrix beams less - see attached half polar. New waveguide concept for RAAL 140-15d.
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File Type: gif Tractrix_JMLC.gif (21.2 KB, 478 views)
File Type: jpg SEOS_Raal_N3.jpg (48.7 KB, 474 views)
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Old 28th March 2011, 12:11 PM   #439
Jmmlc is offline Jmmlc  France
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Hello Jack

Quote:
Originally Posted by jzagaja View Post
Correct and Tractrix is almost two times smaller.
About the way to analyse the directivity maps you obtained from your measurements, my own views will differ somewhat of yours.

I took your maps for both the 200Hz Tractrix and the 200Hz Le Cléac'h horn and removed the frequency above 4500Hz as the response in that range is due to the tweeter part of the coaxial BMS driver which one possess a diameter much smaller than the throat diameter of the horn.

Between 450Hz and 4000Hz I draw two straight lines (white color) passing through the -5dB limits of the polar map of the Le CLéac'h horn and reproduce the same 2 lines on the polar map of the tractrix.

Your polar map for the 200Hz Le Cléac'h horn is consistent with the FEA simulation performed by John Sheerin which one indicate a very smooth variation of the directivity with the frequency (very few refelctions and HOMs inside the horn).

http://ldsg.snippets.org/HORNS/image..._flat_wave.jpg

As we can see on the attached graph is that the directivity of the 200Hz Le Cleac'h is equal or smaller than the one of the Tractrix from 450Hz to 4000Hz.

From 400Hz to 1800Hz the -5dB line fro the the tractrix deviate from the white reference lines and I enlightened the zone comprised between the -5dB line and the white lines. On that frequency interval the directivity is more larger for the Tractrix (more beaming in that frequency range). I intrepret that zone as the result of backreflected, reflected or diffracted waves interfering with the direct wave. This should be probably attenuated if the tractrix horn was included at its mouth to a large planar baffle.

You polar map for the 200Hz tractrix is less consistent with John Sheerin's simulation of a tractrix horn. Most probably the reason is because in John Sheerin's simulation the tractrix horn is inserted in an infinite baffle.

http://ldsg.snippets.org/HORNS/image..._flat_wave.jpg

Best regards from Paris, France

Jean-Michel Le Cléac'h
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File Type: gif compar.gif (62.3 KB, 445 views)

Last edited by Jmmlc; 28th March 2011 at 12:23 PM.
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Old 28th March 2011, 07:52 PM   #440
jzagaja is offline jzagaja  Poland
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Depends on frequency window and normalization.
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File Type: png Tractrix_JMLC_dir.png (71.6 KB, 439 views)
File Type: png Tractrix_JMLC_csd.png (139.6 KB, 127 views)
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