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Testing baffle edge treatments for tweeter diffraction.

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  • 4thtry
    replied
    Thanks. Here is a comparison of modeled vs. actual diffraction for the 7/8 radius round-overs. The top two curves, black and blue, are the on-axis model vs. actual. The 2nd set of 2 curves, green and red, are the 30 degree model vs. actual. And the bottom set of 2 curves, purple and gray, are the 60 degree model vs. actual. Curves are offset for clarity.

    There seems to be a fairly good agreement with the model. I generated these models and blended them using charlielaub "FRD Response Blender 2.0". I also modeled the square baffle curves and they showed fairly good agreement as well. I was unable to model either the Big bevel or Tapering Chamfer curves.

    Click image for larger version

Name:	Modell vs actual diff 7_8_ roundovers- tweeter 4in from top.jpg
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ID:	1427811


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  • DaveFred
    replied
    Originally posted by 4thtry View Post
    DaveFred ,

    I am attempting to compare your curves to various baffle diffraction simulation models. But in order to do so, I need to know exactly how far the tweeter is mounted down from the top of the cabinet (or up from the bottom). We know the baffle is 8 x 15" The tweeter is probably centered horizontally (4 inches from each side). But how far is the tweeter located down from the top of the cabinet? Looks like about 4 inches down from the top of the cabinet in your pictures, but this is only a guess. I re-read the thread but cannot find this value; please forgive me if I overlooked it. Also, how deep is the cabinet? Some modeling programs need the cabinet depth as well. Thanks. Bill
    4" down, cabinet 10" deep.

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  • 4thtry
    replied
    DaveFred ,

    I am attempting to compare your curves to various baffle diffraction simulation models. But in order to do so, I need to know exactly how far the tweeter is mounted down from the top of the cabinet (or up from the bottom). We know the baffle is 8 x 15" The tweeter is probably centered horizontally (4 inches from each side). But how far is the tweeter located down from the top of the cabinet? Looks like about 4 inches down from the top of the cabinet in your pictures, but this is only a guess. I re-read the thread but cannot find this value; please forgive me if I overlooked it. Also, how deep is the cabinet? Some modeling programs need the cabinet depth as well. Thanks. Bill

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  • ergo
    replied
    I've added a zip with 48PPO resolution txt files... should work hopefully. REW allows going down to 3 or 6PPO also if needed

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  • donradick
    replied
    Originally posted by benb View Post

    For what it's worth, here's the result of a diffraction simulator I wrote. I can't do arbitrary shapes, but I think I can do roundovers and square edges. My square edge result is attached. I didn't import the frequency response or anything, so my 1" tweeter has perfectly flat on axis response. Still, I see a lot of similarity. I suspect that either I'm over-estimating the dispersion of the tweeter, or else some detail has been missed in using measurements taken every 15 degrees. More measurements would be interesting.
    Very impressive work, dude!
    I'm not competent to discuss the mathematics of your simulation, but I think some other folks here can get into deep discusssions.
    The most sophisticated software I've seen is "the edge", you might want to compare your results with those simulations.

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  • benb
    replied
    Originally posted by donradick View Post
    Thanks for posted the "txt" files. I used Omnimic and created normalized polar graphs of the square box and big bevel measurements. Clear improvement.
    Click image for larger version  Name:	normalized-square-box.jpg Views:	39 Size:	59.3 KB ID:	1427417
    For what it's worth, here's the result of a diffraction simulator I wrote. I can't do arbitrary shapes, but I think I can do roundovers and square edges. My square edge result is attached. I didn't import the frequency response or anything, so my 1" tweeter has perfectly flat on axis response. Still, I see a lot of similarity. I suspect that either I'm over-estimating the dispersion of the tweeter, or else some detail has been missed in using measurements taken every 15 degrees. More measurements would be interesting.

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  • dlr
    replied
    Originally posted by 4thtry View Post
    It is interesting to note that all baffles seem to depress the 8-12kHz area compared to the IEC baffle.
    It's more likely that the raw driver varies from the published specs in that area. That kind of variance happens more often than not.

    dlr

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  • dlr
    replied
    I think that I can re-map them myself. In the past I've used the free version of Praxis quite a bit for some post-processing, but it didn't seem to work in Win10 last I tried. I just tried it on my Win10 laptop, seems OK.

    dlr

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  • 4thtry
    replied
    All of the files, space or tab delimited, seem to load and display OK in OmniMic.

    I was curious as to how these curves would compare to the published specs on an IEC baffle, so I traced the data sheet curves into an FRD. My tracing skills are not the best, so please take the attached comparison curve with a grain of salt. The bulge and dip from 1-2kHz is obviously the baffle step, which flattens out on the IEC. It is interesting to note that all baffles seem to depress the 8-12kHz area compared to the IEC baffle.

    Click image for larger version

Name:	On-axis comparison to IEC baffle.jpg
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ID:	1427537

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  • dlr
    replied
    Originally posted by ergo View Post
    Thank you DaveFred. I've extracted the txt files out with space and tab delimited format and added a zip file to the same folder above. VituixCAD for example is able to open both without changes
    Any chance you could export those with FFT of maybe 500 instead of almost 54000? WinPCD could import that, but I have a program that doesn't re-map down, so working with 54000 data points is a problem. Plus, it's reading all of the files as well, so I'll have to modify it to re-sample and I don't know when I could get around to that. I suppose I should do that in any case. I'll have to review the code to see if I may also have a bug.

    dlr

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  • donradick
    replied
    Thanks for posted the "txt" files. I used Omnimic and created normalized polar graphs of the square box and big bevel measurements. Clear improvement.
    Click image for larger version

Name:	normalized-square-box.jpg
Views:	271
Size:	59.3 KB
ID:	1427417 Click image for larger version

Name:	big-bevel-normalized.jpg
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Size:	54.1 KB
ID:	1427418

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  • 4thtry
    replied
    Thanks for the additional data. Lots of good information here. Another interesting test would be to mount this particular tweeter (SB Acoustics SB26ST-C000-5) on an IEC-268-5 test baffle and run up the same set of curves. This would give us a better control reference against which to judge how the various baffle board choices affect performance.

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  • ergo
    replied
    One alternate view for each baffle type and offset used for each angle for clarity. 0deg highilighted
    Attached Files

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  • ergo
    replied
    Thank you DaveFred. I've extracted the txt files out with space and tab delimited format and added a zip file to the same folder above. VituixCAD for example is able to open both without changes

    Leave a comment:


  • DaveFred
    replied
    Originally posted by ergo View Post
    Very interesting study DaveFred - Thank you for sharing.

    I created a OneDrive link with write access.
    https://1drv.ms/u/s!AvVPh3wl37Nzm4Qu...ktCxQ?e=YJUFZD
    Would be cool if you could copy the REW files there. Will make it easier to select the type of interest for further study.
    REW raw data file uploaded.

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