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Old 25th May 2020, 08:51 PM   #982
Bob Richards is offline Bob Richards  United States
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On an early page someone asked what DUT meant. I answered before realizing that there were MANY more pages.
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Old 26th May 2020, 08:08 PM   #983
JMB is offline JMB  United States
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Better late than never!
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Old 27th May 2020, 01:10 PM   #984
Hensolo is offline Hensolo
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I take measurements in ARTA and export them to Vituix. The problem is that the frequency response graph is obtained from the bottom up. That is, at 20 Hz the level is 130 dB, and at 20 kHz it becomes 150 dB. I can’t understand where I set up something wrong.
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Old 27th May 2020, 01:25 PM   #985
Hensolo is offline Hensolo
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Quote:
Originally Posted by mbrennwa View Post
Do two loopback measurements

With the wrong polarity, I figured it out this way. In the control panel of the sound card, I turned on the inverse of the microphone input. But I want to get to the truth. I do not quite understand your advice. But I checked such a thing. When I invert both inputs from the microphone and from the speaker in the sound card's control panel, I get a negative impulse again. If I invert only the microphone input, I get a positive impulse. These facts help the investigation of who is to blame?
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Old 27th May 2020, 01:53 PM   #986
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by Hensolo View Post
I do not quite understand your advice.
With a dual channel measurement, the software will deconvolve the DUT (=device under test) signal from the REF (=reference / loopback) channel. If your soundcard inverts the polarity, it will probably do it on both channels. The deconvolution result should therefore have normal polarity.

With a single channel measurement (DUT channel only), there is no deconvolution. If your soundcard inverts the polarity, you will see it in the result.
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Old 30th May 2020, 11:04 AM   #987
Hensolo is offline Hensolo
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I found out who reverses the signal polarity. I connected another microphone to my sound card. It does not invert polarity. Then another one. And this one inverts. These two and mine are capacitor. Two inverts polarity, the third does not invert. Therefore, the sound card is not to blame. The microphone remains. And the question remains. If it changes the polarity of the signal not by 180 degrees, but by 120 or 150, will the phase-frequency characteristic of the speaker obtained by such a microphone be accurate?
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Old 1st June 2020, 08:02 PM   #988
mbrennwa is offline mbrennwa  Switzerland
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If it changes the polarity, this will always look like a 180 degree phase change.
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Old 2nd June 2020, 12:53 AM   #989
pixelpusher is offline pixelpusher  United States
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Phase is a relative thing. If you use the same mic to measure each driver there is no problem.
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Old 2nd June 2020, 09:48 AM   #990
Hensolo is offline Hensolo
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I realized that I can use such a microphone and trust its data. If he biases the phase data, then he does it for all speakers the same way. My question was about data analysis in Vituix. Namely, the phase-frequency characteristic. It matters not only +180 and -180.
If it is not possible to find out how much the microphone shifts these phases, then for now, we must forget this question.
In ARTA, the impulse measurement time step is 0.021 ms. This is 7.2 mm. Those. if you move the microphone 7 mm, ARTA will say add a delay time of 0.021 ms. This is very small. But the phase-frequency characteristic can shift in the HF range by 45 degrees. Is there any criterion to consider that during the measurement I set the delay time correctly? For example, according to the figure of the phase response during the preliminary measurement of the frequency response - FR2?
 

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