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Old 12th December 2012, 02:44 AM   #21
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Originally Posted by OMNIFEX View Post
What is the resolution of the frequency graph? Is there a way to adjust the resolution so it is not so smooth when evaluating frequencies?
Hi OMNIFEX,

Not sure that I understand :-). Hornresp calculates the frequency on a logarithmic scale at every horizontal pixel position on the display screen, so that the chart resolution is the same as that of the screen - there is no smoothing, as such. If you export the calculated results you can see the actual frequencies being used, for your computer. The usual frequency point total for a standard display screen resolution is 533.

Kind regards,

David
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Old 12th December 2012, 02:46 AM   #22
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Originally Posted by Rademakers View Post
+1, hint, hint

Best regards Johan
Hi Johan,

As I have said on numerous occasions - it's not going to happen :-).

Kind regards,

David
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Old 12th December 2012, 03:10 AM   #23
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Originally Posted by David McBean View Post
Hornresp calculates the frequency on a logarithmic scale at every horizontal pixel position on the display screen, so that the chart resolution is the same as that of the screen - there is no smoothing, as such.
Just to clarify - this is the case when the display screen text size is set to 100%.

Strictly speaking, I guess there will be a very slight apparent "smoothing" effect if a larger text size setting is used, because the whole chart will be shown bigger on the screen.

Kind regards,

David
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Old 12th December 2012, 04:20 PM   #24
OMNIFEX is offline OMNIFEX  Jamaica
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Quote:
Originally Posted by David McBean View Post
Hi OMNIFEX,

Not sure that I understand :-). Hornresp calculates the frequency on a logarithmic scale at every horizontal pixel position on the display screen, so that the chart resolution is the same as that of the screen - there is no smoothing, as such. If you export the calculated results you can see the actual frequencies being used, for your computer. The usual frequency point total for a standard display screen resolution is 533.

Kind regards,

David
Hi David.

When I measure the frequency response of my subs, I set the FFT to 32768. This gives me a resolution of 1.35 Hz.

Click the image to open in full size.


This reduces the smoothing from 100 Hz - 20 Hz and gives me more information as appose to having a higher FFT setting.

To make a fair comparison, can you tell me the resolution of horn response within 100 Hz to 20 Hz so I can configure the FFT on my measurement program to match the resolution of horn response to see how well horn response results will match the results of the measured response.


Cheers!
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Last edited by OMNIFEX; 12th December 2012 at 04:30 PM.
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Old 12th December 2012, 10:07 PM   #25
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You may be measuring to 1.35 Hz resolution, but the displayed result depends on the resolution of your screen. As an extreme example, you may have 1000 measured values between 20 Hz and 100 Hz. But if your result graph has only 100 pixels between the 20 Hz and 100 Hz graph lines, that's all the resolution you are going to see.

It's like displaying a picture from a digital camera on a PC screen - the picture might have 3000 x 2000 pixels, but if your display is only 1280 x 1024 you're not going to see all the detail that is in the image.

If I understand David correctly, Hornresp uses variable resolution. It samples at the frequency corresponding to each screen pixel of the result graph. For example, the range 20 Hz to 100 Hz is displayed on a logarithmic scale. There might be 100 pixels between 20 Hz and 30 Hz, so the resolution is 0.1 Hz. But there might be only 10 pixels between 90 Hz and 100 Hz, so the resolution is 1 Hz.

Last edited by Don Hills; 12th December 2012 at 10:12 PM.
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Old 12th December 2012, 10:17 PM   #26
OMNIFEX is offline OMNIFEX  Jamaica
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Quote:
Originally Posted by Don Hills View Post
You may be measuring to 1.35 Hz resolution, but the displayed result depends on the resolution of your screen. As an extreme example, you may have 1000 measured values between 20 Hz and 100 Hz. But if your result graph has only 100 pixels between the 20 Hz and 100 Hz graph lines, that's all the resolution you are going to see.

It's like displaying a picture from a digital camera on a PC screen - the picture might have 3000 x 2000 pixels, but if your display is only 1280 x 1024 you're not going to see all the detail that is in the image.
I have never had that issue you are mentioning. I tend to limit the dB range in addition to use very long sweeps so I would imagine that is why I attain a detail response.
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Old 12th December 2012, 10:38 PM   #27
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Basically. You may well take 32000 or so samples. But your graph won't be showing that detail unless you have a screen that is 32000 pixels wide (which you don't!)

I'm not sure what frequency interval David has set horn resp to calculate but it seems to be a fairly high resolution. It sounds like it is different depending on the size of your screen/graph.
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Old 13th December 2012, 03:16 AM   #28
OMNIFEX is offline OMNIFEX  Jamaica
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Originally Posted by schmeet View Post
Basically. You may well take 32000 or so samples. But your graph won't be showing that detail unless you have a screen that is 32000 pixels wide (which you don't!)
If you are measuring a loudspeaker's frequency response under limited bandwidth, with a limited dB scale, using a slow sweep, I can assure you, there will be a difference in the detail using an FFT scaling of 16384 oppose FFT scaling 4096.

However, if you are using a fast sweep, chances are you will not notice a difference in detail. The key is the duration of the sweep that you are using.
I do not use fast sweeps, I use slow sweeps.

Cheers!
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Old 13th December 2012, 04:42 AM   #29
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Measuring the response of a speaker using a sweep tone is so... last century. The point is still valid though, regardless of the resolution of your measurements, if they exceed the resolution of the output device you won't see them all.

But to answer your original question, Hornresp graphs from 10 Hz to 20 KHz. On my system, there are 49 pixels between 10 and 20 Hz. That's an approximate resolution of about 0.2 Hz per point... for 90 Hz to 100 Hz, there are 7 pixels, that's about 1.4 Hz per point. So the resolution of Hornresp is similar to or better than your measurements at low frequencies. Differences between Hornresp and your measurements will be due to the differences in the models that Hornresp and Eminence Designer use. From my initial examination, ED appears to use the standard lumped constant box model.

Last edited by Don Hills; 13th December 2012 at 04:50 AM.
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Old 13th December 2012, 05:11 AM   #30
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Originally Posted by Don Hills View Post
If I understand David correctly, Hornresp uses variable resolution. It samples at the frequency corresponding to each screen pixel of the result graph. For example, the range 20 Hz to 100 Hz is displayed on a logarithmic scale. There might be 100 pixels between 20 Hz and 30 Hz, so the resolution is 0.1 Hz. But there might be only 10 pixels between 90 Hz and 100 Hz, so the resolution is 1 Hz.
Hi Don,

You understand correctly. To hopefully make things a bit clearer for everyone, I have attached a list of the frequencies used by Hornresp on my computer, over the range 10 Hz to 100 Hz. A full list up to 20000 Hz can be obtained by exporting the chart results data.

I saw no reason for Hornresp to have more frequency points for charting purposes than could be displayed on the monitor screen. It is of course possible to calculated the results at other specific frequencies if desired, using the Sample tool.

Kind regards,

David
Attached Files
File Type: txt Freqs.txt (2.3 KB, 12 views)
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