# Comb filtering or something else?



## Zeitgeist (Apr 4, 2009)

Is this comb filtering, or something else? Seems too noisy to be room modes.

I realize that the level is low, I think that the SPL is mis-calibrated (mostly due to a lower battery in my RS db meter).

Using line input on a laptop, calibration file for EMM-6 mic and I've done the soundcard cal without a problem.

I've done sub sweeps before, but this is the first time that I've done a full range sweep.


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## JohnM (Apr 11, 2006)

All looks pretty normal for an unsmoothed room measurement. The notches once you get much over 100Hz are indeed comb filtering effects due to the direct signal being combined with the reflections from the room's surfaces, which are delayed by the extra distance they travel to the mic.


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## Zeitgeist (Apr 4, 2009)

Cool thank you very much John! I started reading about comb filtering realizing that was probably it. The first page that I found illustrated it with two speakers that weren't time aligned....and the second page illustrated that you can get comb filtering even with a single speaker which is what I was using. 

I never fully understood the usefulness of smoothing but now if makes sense. Thanks!

And now that I finally found my new 9V batteries I can get a better SPL calibration...


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