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An easy to build classic horn?
An easy to build classic horn?
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Old 26th August 2011, 08:03 AM   #11
dabbler is offline dabbler
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Yes i've noticed that the conical gets very big in order to get sufficient for a low cutoff, like an OSWG. See the SPL plot attached for a 30cm long horn (50 degrees) which shows drop off at 800hz then a bump 400 before it drops off steeply. Could we say that the cutoff is at 800? If so should I double the frequency to 1600hz for the crossover point as is done with tractrix and le cleach horns?

Tractrix does have good "bang for buck" in terms of size vs cut-off. Will be interesting to compare the sound to my OS waveguide.
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File Type: jpg con_inp.JPG (55.1 KB, 210 views)
File Type: jpg con1.JPG (41.9 KB, 206 views)
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Old 26th August 2011, 08:25 AM   #12
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by dabbler View Post
It seems that cutoff frequency cannot be entered for a conical horn (F12). Why is that?
Hi dabbler,

A conical horn does not have a specific theoretical cutoff frequency. To illustrate:

Attachment 1 shows the normalised throat acoustical impedance of an 'infinite' exponential horn having a cutoff frequency of 100 hertz. Notice how the resistance (black trace) falls abruptly to zero at 100 hertz.

Attachment 2 shows the normalised throat acoustical impedance of an equivalent 'infinite' conical horn. In this case there is no sharp reduction (or cutoff) in resistance at a particular frequency.

Kind regards,

David
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File Type: png Exp1.png (25.0 KB, 497 views)
File Type: png Con1.png (25.2 KB, 497 views)
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Old 26th August 2011, 08:37 AM   #13
dabbler is offline dabbler
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Hi David, thanks for the explanation and for your program.
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Old 29th August 2011, 06:27 AM   #14
dabbler is offline dabbler
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I am trying to export a tractrix horn design as a rectangular tractix flare however from the dropdown list I can only see the Conical, Exponential and Uni flares?
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Old 29th August 2011, 08:34 AM   #15
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by dabbler View Post
I am trying to export a tractrix horn design as a rectangular tractix flare however from the dropdown list I can only see the Conical, Exponential and Uni flares?
Hi dabbler,

The Con, Exp and Uni options relate to how the width of the rectangular horn is flared. The rectangular cross-sectional area itself still expands as required for a tractrix horn.

Uni is probably the option to choose, unless perhaps you wish to use Con to achieve some degree of constant directivity in the horizontal plane.

Kind regards,

David
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Old 29th August 2011, 12:27 PM   #16
dabbler is offline dabbler
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Thanks David, I'll give the Uni option a try.
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Old 29th August 2011, 01:58 PM   #17
revintage is offline revintage
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Noticed you still use "Constant Directivity" in your sims. This will not help you very much in a mid or high horn. A good starting point is 10 degrees off axis.
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Old 29th August 2011, 03:42 PM   #18
dabbler is offline dabbler
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Hi Lars, not sure exactly what you mean by "you still use "Constant Directivity" in your sims". My latest design is a tractrix horn, I am not aware of how to change directivity other than selcting a conical flare for export. I have used the "Uni" option.
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File Type: jpg TRAC400.jpg (89.5 KB, 134 views)
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Old 29th August 2011, 04:11 PM   #19
revintage is offline revintage
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Its in "SPL response"! When in that window go to Tools/Directivity/Response and choose 10 degrees. This shows the predicted response for horns above basshorns.
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Old 1st September 2011, 06:55 AM   #20
dabbler is offline dabbler
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Thanks Lars, gotcha now. Ive attached a CAD drawing of the square 400hz tractrix which will be made of card. I'll slide in the throat tranistion piece shown at the end.
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File Type: jpg tr3dtrans.JPG (62.3 KB, 33 views)
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