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Klippel Near Field Scanner on a Shoestring
Klippel Near Field Scanner on a Shoestring
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Old 25th September 2018, 08:13 AM   #501
3ll3d00d is offline 3ll3d00d  United Kingdom
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Ok, that's good that you have a lead to follow.

Re power response, DI and scaling, the reason I mentioned it is because I am seeing DI go strongly negative regularly (i.e as the magnitude response moves towards and then beneath the power response). The quote I am working from is in

Add directivity index to the multi view * Issue #10 * 3ll3d00d/pypolarmap * GitHub

Basic terminology check first...

pressure response == the magnitude response i.e. abs(output of linToLog for the input data or output of calPolar for the computed data)

Is any scaling required before doing this? The aforementioned quote mentions scaling to 0dB at 1kHz which I am not doing atm
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Old 27th September 2018, 09:54 PM   #502
3ll3d00d is offline 3ll3d00d  United Kingdom
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I've added a variety of markers and lines to the multi chart view so you can see what data it is showing more clearly

multi_REALWORLD.png
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Old 29th September 2018, 08:43 PM   #503
3ll3d00d is offline 3ll3d00d  United Kingdom
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a release containing the above along with some general improvements to some of the slightly glitchy graphs

Release Polish * 3ll3d00d/pypolarmap * GitHub
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Old 29th September 2018, 11:47 PM   #504
mwmkravchenko is offline mwmkravchenko  Canada
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Klippel Near Field Scanner on a Shoestring
Downloaded.
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Old 2nd October 2018, 06:19 PM   #505
gedlee is offline gedlee  United States
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I am unable to find any errors in what I have on this end.

I have been in touch with Prof. Weinreich (the guy is 90 years old and still quite alert.) We are discussing my ideas for room reflection reduction using a stationary microphone. Time will tell!
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Last edited by gedlee; 2nd October 2018 at 06:22 PM.
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Old 2nd October 2018, 08:59 PM   #506
3ll3d00d is offline 3ll3d00d  United Kingdom
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Quote:
Originally Posted by gedlee View Post
I am unable to find any errors in what I have on this end.
is it worth me putting together a canned example in c#?
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Old 3rd October 2018, 12:04 AM   #507
gedlee is offline gedlee  United States
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We may have to resort to that. Let me keep looking.

How many frequency points are you using? Your plots look so rough compared to mine.
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Old 3rd October 2018, 01:22 PM   #508
3ll3d00d is offline 3ll3d00d  United Kingdom
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Quote:
Originally Posted by gedlee View Post
How many frequency points are you using? Your plots look so rough compared to mine.
it uses

Code:
# no of log spaced points to use given a set number of linear points
logPts = {
    64: 15,
    128: 30,
    256: 50,
    512: 100,
    1024: 200,
    2048: 300,
    4096: 300
}
of course I can change this but there was a discussion earlier in the thread about this, IIRC it boiled down to not using more than 2-300 max and making sure the no of log space points is some fraction of the linear points otherwise things go wrong. Hence it's about 5:1 ratio for most useable window lengths.

there is no interpolation or smoothing on the displayed lines atm either hence the jaggedness
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Old 3rd October 2018, 02:37 PM   #509
3ll3d00d is offline 3ll3d00d  United Kingdom
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the above came from Klippel Near Field Scanner on a Shoestring

Quote:
Originally Posted by gedlee View Post
Try dropping the linear points down to 50 is you are only going to use a small number of data points. For 100 you should have 512 data points or more and 200 should have 1024 or more.
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Old 4th October 2018, 11:15 AM   #510
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by gedlee View Post
....I don't follow "the corrections for near field are done based on a notional source size rather than actually measured"
This is a near field scanner and we need to allow for the fact that the near field does not fall off as 1/r or, equivalently, that the velocity field is not purely radial.
Klippel does measurements at two different radii.
Alternatively we could use only one radius if we measure the velocity field vector with a set of Microflown.
But your software does neither of these, so I assume the near field corrections are done based on the source size that the user nominates.
I don't have your source code to check, of course.
Is that clearer?

I am interested in your idea to do reflection removal if you rotate the speaker rather than the mic.
I don't see how to make it work but it will simplify the mechanics very nicely if you can.

Best wishes
David
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