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Best horn Profile, is there such thing?

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This is a summary of a 128 page Sunday morning read from the master himself, Jean Michel LeCleach' (RIP)

http://www.rintelen.ch/download/JMMLC_horns_lecture_etf10.pdf

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Below is a measurement of 16 horns profile by JMLC again.

JMLC and Kugelwellen horns are obviously the best profiles while on axis. At 40°, not exactly as good, both those horns do "beam" a lot.  The document fails to mention this. Obviously given who wrote it, the inventor of the horn bearing his name may forget to discuss his design flaws... Let's forget him.

http://mariobon.com/Articoli_storici/Horns_measurements_ETF2010d.pdf

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I own a few horn profiles in 1" format. Either the Eminence N151M or CDX1-1425 will be used.

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My friend finished two of four JMLC custom horns.

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Those are for my newly acquired BMS 4526

The horn has a 2000 Hz profile and will be used at 3 kHz and up.

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For testing purposes, he eliminated the lip on the contour of the JMLC horn, left it square and measured the result.

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He then compared it to the finished JMLC with the contour lip.

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Big difference indeed. The extra ripple is significant thru all of the band.

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I've read in several documents, people add a lip to terminate the edge of their horn. This mod obtains great results.

 

This test tends to confirm it.

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Here are 3 horns (all with 1" throat)

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ME10, B&C speaker, has a Hyperbolic Cosine profile, 90° x 60° pattern, 1500 Hz cut-off  (this horn ended up in the garbage bin)

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STH100, Faital Pro, has tractrix profile, 80° x 70° pattern, 1400 Hz cut-off

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Jmlc-2000, Auto-Tech, has a round JMLC profile, a round pattern, 2000 Hz cut-off

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Those 3 different horns will affect four factors (applied 3kHz - 20 kHz)

  1. Frequency response

  2. Exhibits different diffraction (seen on spectrogram)

  3. Distortion (as they load the diaphragm differently)

  4. Time coherence (from different air loading, seen on step response)

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For the following tests below, I've used the Eminence N151M ring radiator, which is basically a cheap copy of the more expensive BMS drivers. (The graph above is provided in eminence datasheet)

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We can see that there's a boost @ 3 kHz - 4 kHz, a flat area @ 4 kHz -10 kHz and a sharp drop afterwards. (this requires equalization to flatten out)

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**The tests below are without equalization**

ME10 horn with the N151M on axis at 12"

Tractrix horn with the N151M on axis at 12"

JMLC horn with the N151M on axis at 12"

Grouped results for better appreciation of differences. 

 

-Frequency response does change a bit from the horn profile, up to 4 dB difference between profiles (EQ can fix this).​

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-Spectogram is cleaner (above 4 kKz) on the JMLC than the other two horns

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-The distortion profile, from the same driver, varies quite a bit, especially the 3rd harmonic being the lowest on JMLC and 2nd harmonic being lowest on the tractrix.  (EQ or DSP can't do anything for correcting distortion)

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-Energy storage is very different. The JMLC recovers faster with less overshoot. (EQ or DSP is useless for correcting this)

Comparing the eminence N151M to the Celestion CDX1-1425 and the excellent Beyma CP22 bullet tweeter for reference.

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On the same JMLC Autotech horn, except the CP22 which is a 40° conical horn.

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  • Cp22 has a tiny breakup at 19500 Hz, but it recovers very quickly

  • CDX1-1425 (metal dome) has a stronger break-up at 16600 Hz and takes much longer to stop ringing as most metal domes do. (mods can fix that)

  • N151M has no break-up at all (spectrogram)

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  • 1425 exhibits significantly less distortion than the other two ring radiators. No surprise here, as it has more radiating surface area. (distortion graph)

  • 1425 has the most storage energy, even in the JMLC horn, the CP22 stops the quickest here. (see step response)

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