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Old 18th June 2017, 09:54 AM   #21
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Good points ICG, I tried today to see if there`s a difference in a measurement with some absorbing material around the mic and without and it seems as this material does compromise the measurement, thanks for pointing this out. Best result I got with the mic absolutely bare. But adding absorbing material on walls/floors does help, tried it too.
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Old 18th June 2017, 11:47 AM   #22
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Default New set of outside measurements

Yesterday evening I have spent some serious time to do some new outside frequency measurements on the Vifa XT tweeter. Conditions are mentioned as in post # 13. Here are the results. Measuring distance 1m and 25 centimeters.
The graphs are without smoothing, if you use the smooting tool the gating marker gets lost.
Attached Images
File Type: png Tweeter 1m june 17.png (37.8 KB, 68 views)
File Type: png Tweeter june 17.png (38.4 KB, 64 views)

Last edited by Piersma; 18th June 2017 at 11:49 AM.
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Old 18th June 2017, 02:58 PM   #23
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Once again, why allways try to compare pears and apples? Why aré you now using 2 different gating times? Cannot simply repeat measuring conditions twice?
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Old 18th June 2017, 03:14 PM   #24
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Default Gating

Here you are...
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Old 18th June 2017, 05:18 PM   #25
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I only see minor differences and i find the .25m distance too unecessarily close as the impulse is relatively free from reflections, except maybe from baffle edges which are the reason for the small differences that can be seen.

Obviously the big thing here is the effect of the foam which makes totally unreliable the response above 10khz.

Btw uncalibrated mikes are not reliable above 5khz. It's ok for designing a standard xover around 2khz, but don't expect real precision for a tweeter measurement.

And trash that foam...Click the image to open in full size.
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Old 18th June 2017, 07:02 PM   #26
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Quote:
Originally Posted by Mario Pankov View Post
Good points ICG, I tried today to see if there`s a difference in a measurement with some absorbing material around the mic and without and it seems as this material does compromise the measurement, thanks for pointing this out. Best result I got with the mic absolutely bare. But adding absorbing material on walls/floors does help, tried it too.
Well, why not using a gated measuring instead of absorbing material on walls/floors? If you already do, the gate is too long or you got still something reflective in too close proximity to the mic or the speaker.
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Old 18th June 2017, 07:27 PM   #27
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Quote:
Originally Posted by GDO View Post
I only see minor differences and i find the .25m distance too unecessarily close as the impulse is relatively free from reflections, except maybe from baffle edges which are the reason for the small differences that can be seen.

Obviously the big thing here is the effect of the foam which makes totally unreliable the response above 10khz.
Yes, the gate is unnecessarily close to the impulse. Why again 1k gate, you've already been told it's too close? The gate has to be set up to exclude the reflections by matching the surroundings, not to the impulse.

And to get comparable measurements, the gate has to stay the same. The measurement comparison seems to be reasonable close together. That is, besides the difference in level. If you equalize it, it seems it's still within ca. +/-1,5dB. Some minor differences there between the measurements but that's likely because of the different placement/angle of the mic.

I'm still not sure if there isn't something else wrong though. Look at the impulse, the green still goes negative first, that's clearly a wrong polarity. Did you change the cables of the mic or the tweeter? I would suggest to try the onboard soundcard instead for a test to clear things up. If that comes out with the same polarity, use the external soundcard and test mic and sound separately. You can also try a test with a loopback.

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Btw uncalibrated mikes are not reliable above 5khz. It's ok for designing a standard xover around 2khz, but don't expect real precision for a tweeter measurement.
No, that's wrong. Uncalibrated mics may not be linear but they don't change the response! So you still get absolutely comparable measurements.
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Old 18th June 2017, 07:46 PM   #28
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Quote:
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No, that's wrong. Uncalibrated mics may not be linear but they don't change the response! So you still get absolutely comparable measurements.
Wrong? If you don't know how unlinear your mike is you will never know how valid is your measurement...

Of course you can still compare 2 measurements made with this mike, but nothing more.

And if you try to design with such uncalibrated stuff you will end tweak your xover by ear, not really because voicing matters, simply because your measurements lack precision in top octave and make you go total blind and you desperately need your ears to check how your trebble sounds...Total waste of time in listening sessions to fix pure masurements issues!
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Last edited by GDO; 18th June 2017 at 07:55 PM.
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Old 18th June 2017, 08:21 PM   #29
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As you can still compare 2 measurements made with this uncalibrated mike i suggest compare the tweeter response at 1m outdoors with and without the nasty foam cap...

With Holm you can still further calculate a corrector for the foam induced low pass filter, in case you insist in protecting your mike from those outdoor wuthering winds...

I am really amazed by how you suspect about everything that might bias your measurements, except about the ... foam cap effect...

Why exactly do you so blindly trust the benefit of using that piece of foam? because it was supplied with the mike?
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Last edited by GDO; 18th June 2017 at 08:29 PM.
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Old 18th June 2017, 09:44 PM   #30
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Originally Posted by GDO View Post
Wrong? If you don't know how unlinear your mike is you will never know how valid is your measurement...
[...]
And if you try to design with such uncalibrated stuff you will end tweak your xover by ear, not really because voicing matters, simply because your measurements lack precision in top octave and make you go total blind and you desperately need your ears to check how your trebble sounds...Total waste of time in listening sessions to fix pure masurements issues!
No, that's completely wrong. Because you've still got all the tools to get the crossover parts correct, and measuring mics actually are very linear, they mostly differ just at the ends of the measuring range. That means, all you have to do with your ears is to realize how much the upper end is off. It doesn't matter if it's +x dB, it will always the same +x dB and once it fits your ear there, keep developing it to the same level there.

So, no time waste and especally no 'total blind'.

Quote:
Originally Posted by GDO View Post
Of course you can still compare 2 measurements made with this mike, but nothing more.
See above. But for most things it is already all you need to be able to compare what you're changing.

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Originally Posted by GDO View Post
As you can still compare 2 measurements made with this uncalibrated mike [...]
He does not measure with an uncalibrated mic, see post #4:

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Originally Posted by Piersma View Post
The testrig is E-MU 0202 soundcard and a calibrated Samson MM01 microphone.
However, he also wrote:

Quote:
Originally Posted by Piersma View Post
The testrig is fully functional and calibrated.
That means, he does use a calibrated mic. And while I believe the mic is calibrated, I have my doubts about the complete calibrated setup though. It's not only about using the calibration file, it's what changes with the DSP, settings etc.

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Originally Posted by GDO View Post
i suggest compare the tweeter response at 1m outdoors with and without the nasty foam cap...
Well, I already suggested that.

Quote:
Originally Posted by GDO View Post
Why exactly do you so blindly trust the benefit of using that piece of foam? because it was supplied with the mike?
I would not trust that cap either. But it got a strong argument for it: It keeps measurements valid by keeping wind noise out (well, to a degree). Ofcourse you are absoultely right, it's not linear anymore then and I would try to avoid the cap to be on but if you always keep it on (or off), you still can measure the difference. And the main thing here isn't if it's linear, it's why it is different.

@Piersma: What amp do you use for measurements? Do you always keep the same level on the amp aswell as on the mixer and Holmimpulse? Any preamp there? Please post the whole measuring chain again.
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