Sound Card Calibration and Impedance Circuit

[John Mulcahy]

Sure

 

[sm52]

I have tried to get Thielle-Small parameters with the double added mass method. Made three measurements. But REW couldn't count. Using the one added mass method, both measurements with different weights allow approximately the same parameters to be calculated. Could you take my measurement files and check the calculation with the double added mass method? Diameter 12.2 cm, Voice Coil DC Resistance 3,36 Ohm

 

[John Mulcahy]

But REW couldn't count

Meaning what?

The measurements show pretty ragged shapes for the added mass measurements. This thread has some discussion of dual added mass that may be helpful and the Speakerbench site has some setup tips.

 

[sm52]

"But REW couldn't count."
DC Resistance 3,36 Ohm. REW asks for a value of around 2.69. Why is it necessary to enter an unreal value? The second message says that my measurements are not correct. However, if you use these measurements separately for the single added mass method, everything counts fine.

 

[John Mulcahy]

Dual added mass allows additional consistency checks. The added mass measurement results are not at all consistent with each other or the free air measurement, hence the very large Bl variation and the warning. Do not rely on any values you get from those measurements.

 

[Bernard]

... This thread has some discussion of dual added mass that may be helpful and the Speakerbench site has some setup tips.

Mr. Claus Futtrup has uploaded 6 videos about SpeakerBench.
Their measurements are made with Woofertester Pro which costs a bit more than REW!
But don't worry, the measurements with REW are just as excellent.
I can testify to that.

Part 1: Introduction >

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Part 2: Collect Measurement Data >

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Part 3: Fit Measurements To Advanced Model >

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Part 4: Create Datasheet >

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Part 5: Box Simulation Intro >

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Part 6: More about Box Simulation > https://youtu.be/pVpfJ-tP11U

 

[sm52]

Hi John. I am taking measurements with a microphone that needs to be inverted. I press the 'invert' button in the sound card control panel. I decided to recalibrate the sound card and enabled this button for loopback input. And I saw that the phase characteristic is first inverted, and somewhere from 600 Hz it changes polarity. The 'invert' button in the sound card panel does its job correctly. In the 'Impuls' window the polarity changes. Is that how it should be? If, after calibration, go to the measurement window and make a measurement without changing the inputs-outputs, then the result is the same - the phase polarity at 600 Hz changes from -180 to +180. Then the phase display in the measurements is incorrect. Soundcard calibration file with amplitude and phase data is always used for all measurements.
And the second question. Bernard in post #31 reported what works better for another topic - https://www.avnirvana.com/threads/t...ment-using-dual-added-mass-method.7058/page-2. Maybe you have the opportunity to move this message to that topic?

 

[John Mulcahy]

If your analog mic inverts but the overall soundcard loopback doesn't run the loopback cal without invert selected and select it afterwards for measurements. There is no polarity change at 600 Hz in the phase trace. Phase is cyclic, -180 and +180 are the same point. What you are seeing is a phase wrap due to the cyclic nature of phase.

 

[sm52]

I tried to measure the impedance of an acoustic wire 5 meters long and 1.6 mm in diameter. A typical device showed 0.2 ohms. I calibrated the sound card to measure impedance. But the measurement turned out to be strange. Can REW measure acoustic cable impedance?

 

[John Mulcahy]

It should be able to, if calibrated accurately.

 

[sm52]

After measuring the inductance impedance, I can click on 'Component model' and see Lsum. Why doesn't the same thing appear for the capacity - Csum?

 

[John Mulcahy]

For inductors the equivalent circuit is an LR2 model consisting of a series resistor, a series inductor and a resistor and inductor in parallel. There is no capacitive component.

 

[sm52]

John, thanks for the answer. I just now realized that I wanted to ask another question. I first measured the impedance of the inductor, pressed 'Component model', and I saw that the calculated Lsum is exactly the same as the readings of a specialized instrument for measuring inductances and capacitances. This was a pleasant surprise. And then I measured the impedance of the capacitance, and clicked 'Component model', but Csum value not was.

 

[John Mulcahy]

So what is your question? If you don't believe the model post the measurement.

 

[sm52]

While I was writing, you have responded to the previous post. My question is in post 38.

 

[John Mulcahy]

It is well hidden then, I cannot see a question in post 38. If you don't believe the model result post the measurement.

 

[sm52]

The red oval marks what I see.

 

[John Mulcahy]

The inductor model has two inductors, so REW shows you the sum of their values to save having to manually add them all the time. There is only one capacitance in the capacitor model so there is nothing to sum, the value is shown next to the capacitor.

 

[sm52]

Thanks for the answer. The inductor and capacitor have a 'Q' parameter. At different frequencies, the Q factor is different for the same capacitor or inductor. A small spread in the quality factor at different frequencies indicates uniform (linear) operation. Is it difficult to calculate and show the Q-factor versus frequency graph? I mean Q = 2 * pi * f * L / R (for inductor).

 

[John Mulcahy]

No, it is trivial, I will look at adding it to the cursor overlay panel.

 

[sm52]

It looks like after the last REW update, when trying to open the .mdat file from the forum, a message appears in the picture. If the file is loaded, it opens in REW.

 

[John Mulcahy]

The error says the file was not found. That location looks like a temporary storage place used while downloading before the file is moved to its intended location, so it had probably already been moved when you tried to open it.

 

[sm52]

I have now checked. The file is downloaded to the Temp folder. Firefox browser prompts you to open or download. By default it is worth opening. I agree. REW is loaded, then this message. Then I go to the Temp folder, there is a file from the forum.

 

[sm52]

John, there is information in the impedance graphs in the lower left corner of the graph. What does it mean? If the cursor is on the graph, I assume it is the data for that point on the graph. As in picture 1. But if the cursor is not on the graph, what does this information show? As in picture 2.

 

[John Mulcahy]

From the help: When the mouse cursor is within the graph panel of the Impedance & Phase graph the equivalent series resistance + inductance or resistance + capacitance and parallel resistance||inductance or resistance||capacitance of the impedance at the cursor position is shown at the bottom left corner of the graph, this is useful when making measurements of inductors or capacitors to check their value. For capacitor measurements the values are most accurate at frequencies where the total impedance has dropped below a few hundred ohms.

It pre-dates the component model, which provides a more accurate representation when measuring inductors or capacitors. The Q or DF value will be shown in that panel.