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Old 5th May 2010, 09:19 AM   #1101
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Hi Everyone,

Quote:
Originally Posted by BP1Fanatic View Post
Ron K wrote: according to Tom Danley, Akabak models quite differently then Horn Response.
Attachment 1 shows the Hornresp power response prediction for the William Cowan 60 hertz tapped horn with Eighteen Sound 10W400 driver, radiating into 2 Pi space.

Attachment 2 shows the AkAbak power response prediction for the same system, radiating into 2 Pi space.

Attachment 3 compares the power response data exported from Hornresp with that exported from AkAbak. The results are not precisely the same because of slight differences in the values of the frequencies sampled by the two programs. I can’t see how the model results could be interpreted as being "quite different", though :-).

Kind regards,

David
Attached Images
File Type: png HR_TH.png (25.2 KB, 240 views)
File Type: png AK_TH.png (25.3 KB, 234 views)
File Type: png TH.png (39.2 KB, 237 views)
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Old 5th May 2010, 10:58 AM   #1102
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Hornresp have multiple times been shown to resemble the real world very accurately.
As long as you know what you model and actually build it.
Both in directivity response, output and excursion.

The biggest gray area is when you start folding a pipe or TH where you simply don't know what you simulate, or how it behave in real world.
Q of resonances differs a lot here, but in a good way.

Time to take the new version out for a test drive now.
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Old 6th May 2010, 08:40 AM   #1103
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Hi Everyone,

Quote:
Originally Posted by David McBean View Post
AkAbak uses a plane wavefront model in all cases, meaning that results can become less accurate once Cir exceeds 1.
Just to explain a bit further.

The following example illustrates the difference between the throat acoustical impedance results produced using a plane wavefront model, and those produced using an isophase wavefront model, for a large-mouth 100 hertz exponential horn.

Attachment 1 shows the plane wavefront model results, identical to those produced by AkAbak, compared to the results for an equivalent infinite horn.

Attachment 2 shows the isophase wavefront model results, as produced by Hornresp, compared to the results for an equivalent infinite horn.

Attachment 3 shows the results for the infinite 100 hertz exponential horn, separately.

For a constant flare, as the horn becomes longer and the mouth becomes larger, the throat acoustical impedance results should tend asymptotically towards the infinite case. This happens with the Hornresp isophase model but not with the AkAbak plane wavefront model.

Kind regards,

David
Attached Images
File Type: png Plane.png (28.8 KB, 213 views)
File Type: png Isophase.png (27.5 KB, 204 views)
File Type: png Infinite.png (25.0 KB, 26 views)
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Old 6th May 2010, 08:51 AM   #1104
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Hi Everyone,

Quote:
Originally Posted by sumsound View Post
David do you make your source code available?
Speaking of source code, some users might find the following of interest.

The attachment shows one of the 80-column Hollerith input punch cards taken from the original Hornresp source code listing. I still have the complete set of cards for the program - they are now more than 40 years old. The deck of cards making up the program is 8 cm thick.

The actual Fortran IV code statement can be seen printed at the top of the card. It represents one line from the subroutine responsible for calculating the throat acoustical impedance of a finite conical horn.

The original Hornresp program ran as a batch file on a room-size mainframe computer :-).

Kind regards,

David
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File Type: jpg Card.jpg (58.1 KB, 98 views)
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Old 6th May 2010, 10:45 AM   #1105
Kolbrek is offline Kolbrek  Norway
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I don't have the data for the horns David posted, but here's a comparison of the throat impedance of a large exponential horn in an infinite baffle (CIR=2), simulated both in Hornresp and in BEM. Again, Hornresp is quite close, and David is right about the fact that the throat impedance gets smoother as the mouth size is increased beyond CIR=1.

Bjørn
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File Type: gif Expo_Z_HR.gif (14.0 KB, 86 views)
File Type: gif Expo_Z.gif (7.5 KB, 27 views)
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Old 6th May 2010, 08:12 PM   #1106
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Using loudspeaker wizard on this data gives me "Run-time error 6: Overflow"

ID=26.40
Ang=2.0 x Pi
Eg=2.83
Rg=0.00
Fta=0.00
S1=100.00
S2=100.00
Con=20.00
F12=0.00
S2=0.00
S3=0.00
L23=0.00
F23=0.00
S3=0.00
S4=0.00
L34=0.00
F34=0.00
S4=0.00
S5=0.00
L45=0.00
F45=0.00
Sd=490.00
Bl=8.50
Cms=1.10E-03
Rms=1.00
Mmd=63.10
Le=1.60
Re=3.60
Nd=1
Vrc=20.00
Lrc=20.00
Ap1=0.00
Lpt=0.00
Vtc=8000.00
Atc=1000.00
Com=MGR 12" BP
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Old 6th May 2010, 09:38 PM   #1107
Mark Kravchenko
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Quote:
The attachment shows one of the 80-column Hollerith input punch cards taken from the original Hornresp source code listing. I still have the complete set of cards for the program - they are now more than 40 years old. The deck of cards making up the program is 8 cm thick.
Boy does that bring back memories!

I just missed punch cards and Fortran. I'm not that old! But I remember having to take all the fundamentals in Computer Science. Thanks for the trip down memory road David.

So if I have this figured out correctly you have been doing horn simulations for what 35 years? Maybe 40?

Explains the thoroughness of the program. And I have yet to see anyone do as tight code as you. All the functionality in still less than a MB. Nice.

THe computers I took programing on were memory enhanced to 32 Kb and ran on Z80 processors. My high level language was the precursor to C. Turbo Pascal. Those were the days when I had hair! LOL

I have but one comment to make on Hornresp's accuracy. The little wierd bandpass variant I worked out checked in as almost perfect to the hz and magnitude of the drivers impedance in box. I have to say I was floored. I think I posted a comment back then and I have unfortunately lost the screen shots but considering that the box was neither a horn or a normal vented or sealed box your method of calulating the resulting output and the impedance magnitude is most impressive.

Mark

Mark
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Old 6th May 2010, 11:25 PM   #1108
soongsc is offline soongsc  Taiwan
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Quote:
Originally Posted by David McBean View Post
Hi Everyone,



Speaking of source code, some users might find the following of interest.

The attachment shows one of the 80-column Hollerith input punch cards taken from the original Hornresp source code listing. I still have the complete set of cards for the program - they are now more than 40 years old. The deck of cards making up the program is 8 cm thick.

The actual Fortran IV code statement can be seen printed at the top of the card. It represents one line from the subroutine responsible for calculating the throat acoustical impedance of a finite conical horn.

The original Hornresp program ran as a batch file on a room-size mainframe computer :-).

Kind regards,

David
If ya still need some blank ones, I have more than 8cm of those. They make pretty good bookmarkers.
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Old 7th May 2010, 08:34 AM   #1109
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Quote:
Originally Posted by Kolbrek View Post
I don't have the data for the horns David posted, but here's a comparison of the throat impedance of a large exponential horn in an infinite baffle (CIR=2), simulated both in Hornresp and in BEM.
Hi Bjørn,

Many thanks for this. I used a somewhat more extreme example than you did, just so that the trend towards the infinite case could be clearly seen. The relevant Hornresp parameter values are Ang = 2,0 x Pi, S1 = 10,00, S2 = 75335,04 and L12 (Exp) = 244,38, giving F12 = 100,00 hertz, Cir = 4,00 and AT = 1,87 degrees.

While a Cir value of 4 is unlikely to be used in practice, the example serves to illustrate the considerable difference between plane and isophase wavefront models when applied to horns with large mouth Fta values. It is certainly necessary to use an isophase model for Le Cléac'h, spherical wave and tractrix horns, to obtain reasonably accurate results.

It is interesting that with the BEM simulation results, the resistive component of the normalised throat impedance appears to tend towards a value just above 0,9 rather than to 1, at the higher frequencies.

Kind regards,

David
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Old 7th May 2010, 08:48 AM   #1110
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Quote:
Originally Posted by David_Web View Post
Using loudspeaker wizard on this data gives me "Run-time error 6: Overflow"
Hi David_Web,

Many thanks for this!

I get the same error - I will let you know when the bug is fixed.

Kind regards,

David
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