Impedance measurement not working - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 24 Old 01-07-16, 09:03 PM Thread Starter
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Evan
 
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Impedance measurement not working

Hi, I've been using Rew for a couple of years, so I do know the basics. I have an old laptop running XP that I use to take room and frequency measurements. I've never been able to make it take an impedance measurement though, so I've always used my desktop for this. I use a homemade jig and it's always worked fine. The thing is is that I've just upgraded to a new desktop computer, so instead of doing all the calibrations again, I would like to get the laptop doing everything because it's already setup for REW and it's just plain easier to take it to a large, heavy speaker than the other way around.

When I try to run an impedance sweep on the laptop I can see something in the small tab graph on the left, but it's obviously wrong and I see nothing on the main graph. I can see a constantly rotating phase response though. And it isn't the graph scaling or the check tab for the measurement. Even if I just try to measure a resistor or inductor, nothing shows up. Does anyone have any ideas to get me moving again? It'd be much appreciated!

Evan
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post #2 of 24 Old 01-08-16, 01:14 PM
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Re: Impedance measurement not working

Difficult to say much without anything to look at, can you attach an example mdat file from a measurement? One of the most common issues is to have the L and R input connections the wrong way around, can check that by just changing the input channel selection in REW's soundcard preferences. What sense resistor value are you using?
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post #3 of 24 Old 01-08-16, 01:52 PM Thread Starter
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Re: Impedance measurement not working

Hi John, thanks for getting back to me.

I'm using a 100 ohm resistor.

It could be that the inputs are switched. It always worked normally on my old desktop, so I never thought to consider that they could be switched. But, since I hadn't heard anything and wanted to measure a new driver last night, I set up REW on my new computer and after doing the impedance cal. My 10 ohm resistor was measuring 110 ohm, After switching the input settings everything is fine. So.... I probably had switched it on the old machine too, because I'm using the same jig.

I'll try changing the settings on the laptop and if it still doesn't work then I attach a sample .mdat file

Evan
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post #4 of 24 Old 06-07-16, 10:16 AM Thread Starter
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Re: Impedance measurement not working

Hi, I hate to bump an old thread, but once again I am having problems with the impedance measurements. Frequency response with a mic works fine. I basically get nothing when I make impedance measurements, regardless of settings, L/R input, etc. This is on two different computers. I've checked the jig and everything looks fine. This is the same jig that I've always used without issues. When I run the calibration (with shorted resistor) I do get the straight line at about 100 ohms. The input seems to clip really easily and I only avoid clipping with a level of -20db or so. Here are a couple of screen shots if they are of any help. Thanks!

Edit: I had to attach them. They are screenshots that I emailed myself from an old laptop I use for measurements.

Impedance measurement not working-impedance-meas.png

Impedance measurement not working-rew-settings.png
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post #5 of 24 Old 06-07-16, 02:49 PM
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Re: Impedance measurement not working

Since it was working and now isn't then a problem with the jig or wiring is the most likely cause.

On the REW setup front it is better to select the soundcard device, input and output directly in the soundcard preferences than to leave things set as default, since Windows may change the defaults depending on what you plug into the PC.
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post #6 of 24 Old 06-08-16, 09:50 AM Thread Starter
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Re: Impedance measurement not working

I'll set up my old computer and try it on that. If it doesn't work then we'll know it must be the jig or wiring.

I tried every combination of devices including selecting the specific devices the computer says it's using. But, I'll set it to those and leave it from now on.

Thanks,
Evan
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post #7 of 24 Old 07-21-16, 09:38 AM Thread Starter
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Re: Impedance measurement not working

Hi, I'm sorry to keep resurrecting this thread, but I still cannot get this to work on either on my current windows computers.

I have checked the jig and everything is good. This worked on my old desktop, but will not work on my old measurement laptop or new desktop. Frequency response measurements work fine on the laptop. One question about the jig- should all grounds be connected together, speaker, input and output? I know that I only use the Right output, but the grounds are common, is that an issue.

I am using the computer's soundcard for impedance measurements and an external amp for frequency response. I could try an amp for impedance, but I'm afraid of damaging the input.

Please see the graphs posted previously as this is still all that I get. A blank graph with a downward sloping graph in the thumbnail. All settings in preferences, ie. input device, output device and left/right input give the same results.

One oddity is that the output needs to be very low to not clip the input. This wasn't the case on my old computer, but maybe the laptop just has a more sensitive input or stronger output. I tried to go back to my old computer to test the jig, but the power supply appears to be toast and it would not power up, hence, why I replaced it when I did.

Any help would be greatly appreciated. I am getting pretty frustrated with this as it worked fine before. If all else fails, I'll just bite the bullet and buy a tester.

Thanks,
Evan
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post #8 of 24 Old 07-21-16, 01:30 PM
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Re: Impedance measurement not working

I just noticed that the version of REW is 'V5' per above screen shot. I believe that version may have had some issue with impedance measurements? That may not be correct. One of the earlier versions had an issue but I don't remember which one. It would is possible to check the change log, but instead I would suggest that you just update to V5.17 or the latest beta version and try that out. It may not be the cause of the problem, but the latest version has more features and less bugs than V5 anyway so it is a more stable release in several ways.

No Joy? If you post a .mdat we can see if there are any other obvious problems with the file.
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post #9 of 24 Old 07-21-16, 01:41 PM Thread Starter
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Re: Impedance measurement not working

Quote:
jtalden wrote: View Post
I just noticed that the version of REW is 'V5' per above screen shot. I believe that version may have had some issue with impedance measurements? That may not be correct. One of the earlier versions had an issue but I don't remember which one. It would is possible to check the change log, but instead I would suggest that you just update to V5.17 or the latest beta version and try that out. It may not be the cause of the problem, but the latest version has more features and less bugs than V5 anyway so it is a more stable release in several ways.

No Joy? If you post a .mdat we can see if there are any other obvious problems with the file.
Thanks, I'll try an update and see. I know the reason that I'm still using V5 is because I had some kind of issue when I updated and had to revert back. This was a year ago or so so maybe it'll work now.

I'll post an .mdat file shortly, don't know why I didn't think of that before
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post #10 of 24 Old 07-21-16, 02:12 PM Thread Starter
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Re: Impedance measurement not working

Ok, now I remember why I'm using an old version- when I try to install the newest version the install fails because it says no JRE can be found. But, When I try to download the latest JRE, that doesn't work either. I am using a seriously old laptop, like circa 2005 that I only use for two programs. It is running XP. The Rew downloads with JRE aren't supported on XP.

My current laptop is a 2014 Macbook Pro, but does Rew work on a mac? I would prefer to keep this software on the old computer if at all possible though.
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