Help With Impedance Measurement Set Up Please - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 7 Old 04-10-17, 06:03 PM Thread Starter
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Help With Impedance Measurement Set Up Please

Hi all

Hopefully you can suggest some help for me please. I'm new to REW and wish to use it for impedance measurements. I have a set up problem that I can't find any advice on how to solve this.

I have a Soundblaster SBX ProStudio and Windows 10.

I have set up the Soundblaster in the preferences and when I do a loop-back test for SPL I get a very sensible looking pair of curves that match well with other Soundblaster curves I've seen on here.

I have built the Rsense measurement jig according to the diagrams and with a non-inductive resistor of 100 Ohms using the sound card's headphone output and mic input. For the impedance tests I have a heathly -11dB level set and no input from my laptop's microphone.

I have run the impedence calibration test (Rsense shorted) and I get a reading of 102.3 ohms for my resistor. Then, when I short out the load connections (Rsense no longer shorted) I get a very high resistance measure - in the 3 to 6 MOhms range. But using a multimeter I get sub 0.1 ohm measurements on on the cables and connections. So the -ve output from sound card to -ve input or -ve speaker gives me sub 0.1 ohm measurements, as do the connections from output to Rsense and input to Rsense.

Of course, this MOhm measurement on the cables gives me very silly measurements on speakers too.

Any help you can offer please?
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post #2 of 7 Old 04-24-17, 02:46 PM Thread Starter
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Help With Impedance Measurement Please

I posted a similar request in the REW sub-forum but there has been no response, so perhaps there is more help to be had in the DIY speaker forum.

I'm trying to measure speaker impedance and phase for crossover design, using REW.
Hi all

Hopefully you can suggest some help for me please. I'm new to REW. I have a set up problem that I can't find any advice on how to solve this.

I have a Soundblaster X-Fi and Windows 10.

I have set up the Soundblaster in the preferences and when I do a loop-back test for SPL I get a very sensible looking pair of curves that match well with other Soundblaster curves I've seen on here.

I have built the Rsense measurement jig according to the diagrams and with a non-inductive resistor of 100 Ohms using the sound card's headphone output and mic input. For the impedance tests I have a heathly -11dB level set and no input from my laptop's microphone.

I have run the impedence calibration test (Rsense shorted) and I get a reading of 102.3 ohms for my resistor. Then, when I short out the load connections (Rsense no longer shorted) to check on the resistance of the leads, I get a very high resistance measure - in the 3 to 6 MOhms range. But using a multimeter I get sub 0.1 ohm measurements on all the cables and connections. So the -ve output from sound card to -ve input or -ve speaker gives me sub 0.1 ohm measurements, as do the connections from output to Rsense and input to Rsense.

Of course, this MOhm measurement on the cables gives me very silly measurements on speakers too.

Any help you can offer to explain what I'm doing wrong please? Thanks
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post #3 of 7 Old 04-25-17, 08:27 PM
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Re: Help With Impedance Measurement Set Up Please

Did you ever solve this problem? I have been trying to get impedance measurements and I am getting the same kind of results. I see a very high measurement of around 4 MOhms. I am using Windows 10 on an HP laptop. I've tried using both the internal sound card and a cheap external USB soundcard. I have no idea how to troubleshoot the problem.
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post #4 of 7 Old 04-25-17, 08:53 PM
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Re: Help With Impedance Measurement Please

The 102.3 for 100 ohms R sounds reasonable, but the leads test is erroneous/failing. Can't really help you without looking into it further, I plan to get a setup on REW for driver measuring someday because my WT3 is so flaky. The WT3 has a very similar calibration procedure, but all I can tell you is that the bad readings mean something isn't working right.

Mega ohm range usually means an open circuit (loose or bad connection). Or, something on the soundcard isn't right.
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post #5 of 7 Old 04-27-17, 11:29 AM
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Re: Help With Impedance Measurement Set Up Please

Why not save your self all the headaches and hassle, and just buy the DATS V2 ?

http://www.daytonaudio.com/index.php...st-system.html


Worth every penny.
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post #6 of 7 Old 06-21-17, 09:56 AM
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Re: Help With Impedance Measurement Set Up Please

Is there any reason why an ASIO driver shouldn't work for impedance measurements? I wasn't able to get the calibration working correctly until I switched to Java driver. With Asio the impedance curve was not stabile over frequency. It had huge peaks and drops, while the average (or smoothed) results were around 100Ohms as they should be. The result with Java driver was perfectly smooth, eventhough it was challenging to turn the input sensitivity knobs accurately enough to get the level withing +/-1% (99-101 Ohms).
I work with an Focusrite Scarlett 18i8 and the Win 8.1. The mixer control user interface of the 18i8 is quite complicated. Too many ways to miss-route the signals. Anyway, I'm not going to change the soundcard.
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post #7 of 7 Old 06-21-17, 02:16 PM
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Re: Help With Impedance Measurement Set Up Please

Saw something like this once before, not so long ago. In that case it looked like the ASIO driver had a big timing offset between the channels, which was very odd. No reason not to use the Java driver though.
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