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Discussion Starter · #1 ·
Hello everyone. Please forgive me if this question has been answered before; I couldn't find it.

I'm trying to use the CM-140 manually, without Room EQ Wizard, by adding the correction values in the REW cal file and the standard C-weighting curve to my measurements. According to this post by member LPS:

"If you intend to use the CM-140 to record /analyse the sound externally, you will need to take the A or C weighting into account, plus the microphone response (this is what the "calibration files" are for).

This seems (to me) to indicate that I should add the two correction values together, so at 20Hz, for example, I would add 13.52 dB to the meter reading. However, in the Room EQ Wizard Help Index, Mic/Meter Settings section, it states:

"Select the C Weighted SPL Meter check box if you are using a C weighted SPL meter as the input to REW, measurements will then be corrected to remove the low and high frequency roll-offs of the C weighting characteristic. If a cal file is loaded the correction will only be applied outside the frequency range covered by the cal file."

I'm confused by the statement in bold. The cal file seems to cover the entire audible frequency range, therefore I should not add C-weighing to the cal file. Should I add the two correction values together, resulting in a 13.52 dB correction at 20 Hz, or add only the 7.32 dB from the cal file? Thank you very much for your time.
 

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Welcome to the Forum, Bert!

Anything you see regarding the CM-140 meter and REW only applies for using the meter with the REW program. If you’re taking manual SPL measurements in your room using frequency-specific test tones, none of that applies. In that case, just add the dB value from the calibration file for the test tone that you’re taking a measurement of.

Regards,
Wayne
 

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Discussion Starter · #3 ·
Thanks for the speedy reply, Wayne. I suspected something was wrong when my corrected measurements showed a rising response above 10kHz. They look better now. :)

Also, thanks to those responsible for the cal files and the general help I've found at this site so far. I hope someday I'm able to return the favor.
 
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