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Old 20th August 2010, 10:47 PM   #1
teodorom is offline teodorom  Italy
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Default If anybody is still interested in fiber, air, models in a duct ...

... can have a look on Audio and Mathematics.
More to follow !
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Old 21st August 2010, 07:33 AM   #2
gedlee is offline gedlee  United States
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Impressive work!

I have gotten disappointed in MathCad and recently bought Mathmatica, but only played with it. From what I could see MathMatica is far and away a better program than MathCad, but the learning curve is steep.
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Old 21st August 2010, 09:55 AM   #3
teodorom is offline teodorom  Italy
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Mathcad versus Mathematica ... an old story !
When first in IBM, in the early 1981, I was teached how it was difficult to have a menu-based, user friendly, counterpart of a command-based environment.
I lived with this dicothomy during the years, with Windows and now with Audio and Mathematics.
Sure, the good news is that with Mathematica you have much more control than with Mathcad, the bad news is that you MUST have much more control.
There are other things that are worrying me: the role of the deferred evaluation, the way how Mathematica evaluates expressions, numerically versus symbolically, the rough way of handling units of measure (Mathcad is far superior in that), and so on ...
So ... I was unable to repeat the calculations I have done with Mathcad on the fiber behavour. Mathematica was so slow ! so slow that it was impossible to repeat the optimization I have done with the T/S parameters of the loudspeakr used by MJK. It is certainly my fault, that is of my inability of have a full control of Mathematica.
I shall show nextly how to do the Hilbert transform leading from the magnitude to the phase of a loudspeaker, using the Gauss-Tchebychev integration. It takes a few seconds ! (with Mathcad). These are the same calculations made by the "mytical" Paul Verdone in his spreadsheet (or, better, in his hundreds of VBA lines of code, impossible to decypher).
For the moment Mathcad is "good enough" for me.
What difficulties you had with it ?
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Old 21st August 2010, 10:30 AM   #4
john k... is offline john k...  United States
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Nice work Teodoro.

Paul and I worked on the MO extraction. His Excel based code used a discrete, FFT approach to MP reconstruction. The problem is that the FFT approach forces the phase to zero at the frequency extremes. Paul worked around that by some convoluted method that segments the frequency response and patch the results for each segment together. I tried to convince him to use the basic integral approach which I wrote a routine for and was very fast. I still do everything in FORTRAN and use FORTRAN routines called from EXCEL. I use Excel for a user interface and plotting. But the FORTRAN codes are much, much faster than using MathCAD.
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Old 21st August 2010, 10:51 AM   #5
teodorom is offline teodorom  Italy
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Hi John,
for shure FORTRAN is much faster than Mathcad !
However Mathcad is much more transparent, and with the Gauss-Tchebychev polynomial integration is as fast as the Paul Verdone calculations.
Thanks again for your support (now and then: you explained to me a lot of things !).
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Old 21st August 2010, 12:47 PM   #6
gedlee is offline gedlee  United States
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BIG chuckle here!! I too still do numerical analysis in FORTRAN!! There is nothing like it for speed. I use VB as a front end and and plotting since it is far more flexible than EXCEL. I am doing custom analysis software here in China for people who have never even heard of FORTRAN. I only laugh. I use MathCAD to develop the algorithm and then use FORTRAN when I get seriuos. I have MathCAD programs that take hours and FORTRAN does them in minutes.

I like MathCAD, always have, but when they were bought recently the customer service went all to He11. I really have not use Mathmatica enough to make a choice, and what you say could be quite true.
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Old 21st August 2010, 04:41 PM   #7
speakerdoctor is offline speakerdoctor  United States
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Default More theory on polyester fiber in closed boxes

Has anybody visited here:

http://auralization.blogspot.com/?zx=5a5a0210d53820a4

It's a blog spot by Ken Kantor. However, the technical paper on PET fiber posted there is by John O Hanlon.
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Old 21st August 2010, 05:11 PM   #8
teodorom is offline teodorom  Italy
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Thank you, I shall try to work on it.
I feel however that the measurements presented by JO tell only part of the thruth.The ideal measurements can be done only by an impedance tube, a two microphone technique and so on ...
The methods (mainly the measurement of the electrical impedance of a loudspeaker in a TL) used by MJK (on polyester fiber) and by R.A. Robinson (a student of Marshall Leach, on fiberglass) are just "good enough".
Some improvement, I guess, could be obtained by measuring the loudspeaker impedance not only with the "open" TL, bu also with the "closed" TL.
If the measurements are precise enough the could give both the (complex) speed of th sound and the (complex) density of the air.
I know, I should do the measurements ...
I have the loudspeaker, the tube ... I dont have yet the appropriate sound card to be used with Speaker Workshop.
Given my pace, it will take years !
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Old 25th August 2010, 08:04 PM   #9
teodorom is offline teodorom  Italy
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I have just added a "paper" on the Wilson model. Always on polyester fiber.
I'm still working on fiberglass.
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Old 26th August 2010, 12:55 AM   #10
gedlee is offline gedlee  United States
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Why the fascination with fiber? Seems to me that the understanding that we have is perfectly sufficient for the needs.
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