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Old 14th August 2011, 02:58 PM   #2101
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The impulse response for both small and large Vrc.
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File Type: jpg 12PE32 60Hz tractrix impulse dark.JPG (29.2 KB, 211 views)
File Type: jpg 12PE32 60Hz tractrix impulse light large.JPG (31.8 KB, 212 views)
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Old 14th August 2011, 07:10 PM   #2102
Mark Kravchenko --- www.kravchenko-audio.com
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The impedance peak is a function of the driver in the rear enclosure coupled to the horn.

When you have the same acoustical impedance on the front and the back of the cone you have an ideally loaded horn. That is the general goal of reactance annulling.

You have described the variables quite well.

It's all about compromise.

If you want to tailor the roll off below the Fc of the horn you can increase the size of the rear enclosure. But there are penalties to be paid in such an endeavor. Loss of efficiency and proper control of the drivers behavior.

There is much more to be described. And there are a few gentlemen on this thread that are very capable of fleshing this out, or correcting anything that I may have erred on.
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Last edited by mwmkravchenko; 14th August 2011 at 07:11 PM. Reason: Second sentence missing wurdz
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Old 14th August 2011, 10:33 PM   #2103
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Quote:
Originally Posted by mwmkravchenko View Post

When you have the same acoustical impedance on the front and the back of the cone you have an ideally loaded horn. That is the general goal of reactance annulling.
When I use the exact calculated values, I get the -3dB point at the horn cut off and excursion is controlled. A small resonance peak remains in the electrical impedance curve however. If Hornresp is an accurate representation of reality, then the Keele and Leach equations are accurate as well. Attached are the results using 2 different equations to determine the Vrc. It does appear to be a compromise and measuring the electrical impedance such that the curve does not have any peak in order to determine the best value for Vrc seems to be a mistake.
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Old 14th August 2011, 10:51 PM   #2104
Mark Kravchenko --- www.kravchenko-audio.com
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When I use the exact calculated values, I get the -3dB point at the horn cut off and excursion is controlled.
Remember that all these "exact" formulas are best worked out mathematical representations of what happens in the real world. The real world is where "exact" lives. And "exact" has an evil sense of humor. I think he is related to Mr. Murphy of long quoted axiom.

What I can tell you is that I have been using Hornresp since 2002 and it is one of the best most versatile acoustical simulation programs that I have ever fooled around with. And it can be extremely accurate. The caveat being that you build exactly what you have simulated. I have posted many examples of measurements agreeing with simulations.

Your questions are leading towards what kind of a horn? Theoretical or real?

When you build the horn you can then make changes on the rear chamber and measure their resulting changes.

Keep in mind to that you are simulating a perfect circular horn. If you make anything other than that, in the mid to high frequency range you will be making further compromises. That to will change the way in which the acoustical impedance varies with frequency in the throat and how a rear chamber will help you to mitigate most of these variances. Reactance annulling really occurs over a relatively narrow band of frequencies close to the Fc of the horn.

It is all a matter of balance. Compromise in one area for another.

Hard and set formulas and exact calculations are mere figments of our imaginations..

We are simulating best guesses and their hoped for results.

What you build is the final arbiter. And how it sounds is what really matters.



If you want a given Tractrix horn the first thing you may want to figure is building it to accomplish the required low end . They roll off rather quickly in real life. A variant by Jean Michel LeCleach is better suited to what you seem to be after.
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Old 14th August 2011, 10:59 PM   #2105
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Quote:
Originally Posted by mwmkravchenko View Post

Your questions are leading towards what kind of a horn? Theoretical or real?

If you want a given Tractrix horn the first thing you may want to figure is building it to accomplish the required low end . They roll off rather quickly in real life. A variant by Jean Michel LeCleach is better suited to what you seem to be after.
I designed a 1/4 size 60Hz tractrix horn for the B&C 12PE32 driver using a spreadsheet and simulated it in 1/8 space in Hornresp. I've attached the input screen for Hornresp. I've already purchased the drivers. I just want to finalize the design and answer some questions. I found that the horn simulated much better in 1/8 space than in 1/4 space. In 1/8 space it actually goes down to the designed cut off of 60Hz. Tractrix bass horns are known for not extending down to the cut off frequency. The shape of the horn is going to be a typical Edgar style with 2 straights sides and 2 curved ones.

Can you provide a source for designing a LeCleach horn? I need a spreadsheet or something.

Thank you very much for your help and insight! Much appreciated!
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File Type: jpg 12PE32 60Hz tractrix input screen.JPG (57.1 KB, 46 views)

Last edited by dirkwright; 14th August 2011 at 11:03 PM.
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Old 14th August 2011, 11:09 PM   #2106
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Can you provide a source for designing a LeCleach horn? I need a spreadsheet or something.
It's in Hornresp!

Read the manual.

1/8th space is a very optimistic place to be that does not really exist in normal listening environments where you would be using this type of a horn.

Simulate it in 2 Pi and see what you get.

And if you are close to a wall and have good boundary reinforcement from say a concrete basement you could get away with 1 Pi.

1/8th Pi only really works with a concrete floor walls an ceiling.

As in perfectly reflective surfaces.
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Old 14th August 2011, 11:23 PM   #2107
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Quote:
Originally Posted by dirkwright View Post
When I use the exact calculated values, I get the -3dB point at the horn cut off and excursion is controlled. A small resonance peak remains in the electrical impedance curve however. If Hornresp is an accurate representation of reality, then the Keele and Leach equations are accurate as well. Attached are the results using 2 different equations to determine the Vrc. It does appear to be a compromise and measuring the electrical impedance such that the curve does not have any peak in order to determine the best value for Vrc seems to be a mistake.
I do believe the acoustic impedance should be used to design the horn, and the electrical impedance is best used to design the back chamber.
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Old 15th August 2011, 06:29 AM   #2108
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Default Hornresp Version 28.70

Hi Everyone,

The latest Hornresp release (Product Number 2870-110815) has the following two new features:

1. Four-segment tapped horns can now have the mouth-end driver entry point at either S3 or S4, as requested by Dan. To select the four-segment S3 driver position option, double-click on the red TH label when in edit mode to change to TH1.

2. The Compare function has been extended to the System Efficiency, Sound Pressure and Particle Velocity charts, as suggested by Oliver. Functionality remains the same as for other charts - previous results are used in comparisons by default, but results can also be captured or released by right-clicking the relevant chart and selecting the appropriate popup menu command, or by pressing Ctrl+C to capture the current results or Ctrl+X to release captured results.

Could you please let me know if you find any bugs. Thanks.

Kind regards,

David
Attached Images
File Type: png Tapped1.png (23.7 KB, 54 views)
File Type: png Tapped2.png (16.5 KB, 57 views)
File Type: png Compare.png (22.5 KB, 54 views)
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Old 15th August 2011, 07:14 AM   #2109
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Quote:
Originally Posted by dirkwright View Post
I designed a 1/4 size 60Hz tractrix horn for the B&C 12PE32 driver using a spreadsheet and simulated it in 1/8 space in Hornresp.
Hi dirkwright,

The tractrix horn you are proposing has a severely truncated mouth. In such cases a simple exponential flare having the same S1, S2 and L12 values will normally perform just as well. Tractrix and Le Cléac’h horns are really intended to have fully-formed mouths. Otherwise, there is little to be gained in using them - it is just an unnecessary complication :-).

Kind regards,

David
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Old 15th August 2011, 12:46 PM   #2110
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Quote:
Originally Posted by David McBean View Post
Hi dirkwright,

The tractrix horn you are proposing has a severely truncated mouth. In such cases a simple exponential flare having the same S1, S2 and L12 values will normally perform just as well. Tractrix and Le Cléac’h horns are really intended to have fully-formed mouths. Otherwise, there is little to be gained in using them - it is just an unnecessary complication :-).

Kind regards,

David
If that is the case, then the spreadsheet I am using is wrong.

The horn length in your software does not match the length shown by the spreadsheet I'm using.
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File Type: jpg 12PE32 tractrix spreadsheet.JPG (72.4 KB, 42 views)

Last edited by dirkwright; 15th August 2011 at 01:01 PM.
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