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RE: optimal horn type

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In Reply to: RE: optimal horn type posted by ogima on May 30, 2007 at 11:10:54

Hello,

70Hz to 800Hz is more than a decade. That's a very difficult task for any horn to cover such a large interval of frequency

Even the Ale Horn reference EX70 covers only the interval 100Hz to 500Hz
http://www.tachyon.co.jp/~sichoya2/ale/horns.html

Most "snail horns" cannot cover a decade the only exception being the WE15A :
http://www.audioanthology.com/building.htm
and its variations like the WE22A: http://members.jcom.home.ne.jp/atrc/page026.html

(unfortunately the WE22A must be cut at 150Hz or 200Hz min). This feature on WE horns is due to an equilibrium between pure horn loading at low frequency and reflections of waves on the outer wall at high frequency. This was obtained by an emprirical but clever balance between curvature radius and thickness/width ratio of the sections in the curved part of the horn. Unfortunately Ale curved horns don't use sections having a large ratio width/thickness in their curved part and they cannot be used over a large interval of frequency.

If you cannot afford a WE15A, better to use a straight horn to cover such large interval of frequency.
Conventionally, if you want to cut electrically at 80Hz you should use a 40Hz maximum acoustical cut-off but at low frequency we are less sensitive to phase ditortion (or more accustomed to, eg. bass-reflex...)so IMHO it is not necessary and you may use a horn with a 80Hz cut-off.

It will be also interesting to play with reactance annulling at throat but this is not easy when using a compression driver.

Then, if you want to avoid any resonance (tuned pipe effect), you have to use a quasi infinite horn, this means a mouth opening at 180 degres minnimum and the dimensions will be large. (horns having a "cut mouth" tend to have a recognizable "horn sound" and cannot be used over a large interval of frequency with good results: eg: Goto and Ale straight horns).

For any Tractrix, Kugelwellen or for a horn having a profile calculated by my method (horn having a 80Hz cut-off and calculated for a 75mm throat), the outer diameters will range between 1,8 meter (71 inches) to 2,6 meter (102 inches) and the length between 1,9 (75 inches) to 2 meter (80 inches).

Best regards from Paris,

Jean-Michel Le Cl�ac'h

Follow Ups:

RE: optimal horn type - angeloitacare 03:24:59 05/31/07 (4)
bonjour Jean Michel

can you explain me why Avantgarde and others do use a > 50cm diameter midrange Horn above their 95cm diameter mid-bass horn, if it does only have to cover > 500hz, and theoretically only a 20cm diameter horn would be needed ?

rds Angelo
- RE: optimal horn type - Jmmlc 05:00:08 05/31/07 (3)
  Hello,
  
  There is several possible answers to that question but here the most logical:
  
  - in order to operate the horn inside a frequency range for which the acoustical impedance of the horn is mainly resistive (and not reactive in order to avoid phase distortion) we have to use a high pass frequency an octave minimum above the acoustical cut-off frequency of the horn. This means that for a tractrix horn used above 500Hz, the acoustical cut-off should be 250Hz. If we consider a complete tractrix horn opening at 180 degrees this means a horn having a 433 millimeters diameter.
  
  Please notice: classical empirical formulas giving relations between cut-off frequency and diameter give a minimum diameter. IMHO thet can be useful in the pro domain where a smaller volume is desired. In the hifi domain they should be avoided.
  
  Martin Seddon in Australia and Marco Henry here in France did listening tests on horns calculated with my method and having cut-off frequency around 160Hz. There conclusion are similar: a JMLC round horn with a profile opening at 360degrees is better than a JMLC horn opening at 180 degrees.
  
  For horns: larger is better!
  
  Best regards from Paris.
  
  Jean-Michel Le Cl�ac'h
  - RE: Thanks Jean-Michel - ogima 07:55:17 05/31/07 (0)
    Jean -Michel,
    
    Thanks for taking the time to respond with such clear understanding of
    the subject as well as the courtesy expressed.
    
    Dan
  - RE: optimal horn type - angeloitacare 05:18:54 05/31/07 (1)
    Hi Jean-Michel
    
    so this would apply also for 88cm mid-bass horn? Meens if acoustical cut-off of the horn is 125hz, the upper bass driver would have to be low pass at 250hz ?
    
    Angelo
    - RE: optimal horn type - Jmmlc 07:43:25 05/31/07 (0)
      Hello,
      
      That's right.
      
      The only exception is if you process the signal sent to the loudspeakerwith a DSP in order to obtain a linear phase signal at the mouth .
      
      Best regards from Paris,
      
      Jean-Michel Le Cl�ac'h

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