# Error during Sub Measurement



## SamSpade (Jun 3, 2010)

I am receiving an error message during my sub measurements. After I make a measurement, an error box opens and states: "Impulse peak is not where it should be, the measurement may have been corrupted. Check the Impulse Response and the captured data points."

My setup is: a Behringer ECM8000 (calibrated by Cross-Spectrum Labs) connected to a Behringer 502 preamp. The preamp is connected to the SoundBblaster 24 bit Live! External card. The SB card is connected via USB to my laptop that is running Windows 7. The output of the SB card is connected to an input on my Lexicon MC-12 processor. The sound card has been calibrated and the mic calibration has been put into a file that is used by WAV.

My first step was to follow the “Check Levels Procedure.” I selected the Soundcard menu from the Preferences option. For “Levels,” I chose “Use Subwoofer to Check/Set Levels.” The Sweep Level is set at -12dB FS. Wave Volume is set at 1.000, and the Output Volume is set to 0.500. I then clicked on “Check Levels.”

Then, I clicked on “Next” and heard the pink noise coming from my left subwoofer. I adjusted the volume level on my audio processor until my Radio Shack SPL meter read 75dB at my listening position. Looking at the Right vertical bar meter, I adjusted the “Main Mix” gain of the preamp until the bottom number labeled “dB FS” on the Left bar graph read -18dB.

Finally, I calibrated the SPL reading. After selecting the “SPL Meter” in the top menu bar, I selected “SPL” “C Weighted” and then clicked on “Calibrate” box and heard the pink noise play through my left subwoofer. Because I had already adjusted the volume of the subwoofer amp to read 75dB at my listening position, I didn’t have to change the “75dB” reading in the “SPL Reading Calibration” box. So, I clicked on the “Finished” button.

I opened the “Make a Measurement” window. Here is the graph I got:









Here is the Impulse Response I got:









The warning box also said I should check the "captured data points," but I don't know what that is referring to.

Would someone tell me what I am doing wrong?

Thanks.


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## laser188139 (Sep 19, 2009)

When I've had this error message, I usually noticed a glitch in the sound, like static, sometime during the sweep. Usually running the sweep again would make the warning go away. If need be, you can reduce the Length of the sweep, or the Number of sweeps, to reduce the time required and thus the probability of a random crackle interfering with the sound. 

In the Impulse graph Controls, there is a check box, Show points when zoomed in. I expect this is what the message was talking about, but you have to really zoom in a lot to see the dots themselves. 

Bill


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## JohnM (Apr 11, 2006)

The message about the captured data means the "captured" trace on the scope plot, which shows the actual waveform received during the sweep - best to take a look at it and make sure the signal does not have gaps or glitches in it (you will need to zoom in to see the progress of the sweep).


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## SamSpade (Jun 3, 2010)

I will try that but I have run this measurement at least 10 times and get the same error message each time.


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## SamSpade (Jun 3, 2010)

*Help!*

I am taking this week off from work and my main goal was to use WAV to get accurate measurements of my mains and sub. I believe I have good data for my mains, but this problem with measuring my subs has me stumped. I have looked followed the advice given so far, but every time I run a measurement of one of my subs, I get the same error message.

Would someone give me another idea on how to solve this problem?

Thank you


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## laser188139 (Sep 19, 2009)

*Re: Help!*



SamSpade said:


> ... Would someone give me another idea on how to solve this problem? ...


Can you use a different computer? Sometimes noise issues present with a laptop are not present when using a desktop computer, and vice versa. 

Or you could just ignore the warning. On the frequency response curve, the only visual glitch appears at 120Hz, which might be related to the warning, and you are not likely to do any equalization that high anyway. 

Bill


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## SamSpade (Jun 3, 2010)

I think I have solved the problem I was having. I downloaded WAV again and gave it a new name. When it was download, I saw a message (I'm sorry, I don't remember the exact text of the message) that gave me an option to select "tweaks" to the program to avoid possible errors in the compatibility of WAV and my OS. Since I am using Windows 7, I allowed the "tweaks" to be used.

My next measurement of my right sub did not display the error message about the location of the impulse response. Here is how my measurement looked:









Here is how the Impulse Response measured:










Even though I did not receive an error message regarding the Impulse Response, I am concerned about the validity of my SPL measurement. Would someone tell me if the Impulse Response is in the ballpark for the measurement of a sub?

Thanks again for all of your help.


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## laser188139 (Sep 19, 2009)

Your new sub impulse graph looks much closer now to mine. It actually decays a little more quickly than does my room. The difference between this one and your earlier graph is obvious. 

I can't tell the differences in the frequency response curve, as this one has smoothing, and it's a little unsettling to see the frequency axis linear instead of logarithmic. 

Good luck,
Bill


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