Guys, my point is that once you have at least one known calibration file (like 0 degree for the UMIK-1) for your mic then it's possible to generate another calibration file (like 90 degrees) from it and load it into REW. I'll come back later this evening to expand on my (brave) idea with a lot of reasonings. Stay tuned, please!
First of all I’d like to thank Jerry for not sparing his time and effort again for providing different graphs showing test mic behaviour with different orientations. Highly appreciated!
Of course, I do agree that the best is to have a set of calibration files with different orientations prepared by specialists, but I’d like to talk a bit about the UMIK-1 (or any other mic with only 1 cal file) as an example with an idea to discuss how a self-generated cal file can be produced for 90 degrees when only the 0 degree file is provided by the maker and how the UMIK-1 owners or wannabee owners can regain their self-esteem and feel like half a man no more before cancelling their orders or shipping back/selling out their stock.
Before going into details, let’s review again some aspects of measuring mics:
1. I think we can easily agree that the directionality of the mic is only relevant at the high frequency end of the audio spectrum, while the lower we go down the importance becomes less important in view of sensitivity. Finally, down at the Bass Department the orientation makes no difference, for such large wavelenghts the mic can be in any position, up or down or on-axis or even showing it’s back side to the sub.
2. As it was mentioned by Jason in an earlier post, most of the commercially available test mics use a Panasonic capsule, therefore the basic characteristics will be more or less similar, while some deviation may be attributed to the housing. Namely they will have a pretty flat response up to about 3-4 kHz and the curve will have a peak around 13 kHz, from thereon it will start to rolloff. This 13 kHz peak will be somewhat higher for on-axis and somewhat lower for grazing incidence.
3. The range above 10 kHz will be of less importance when it comes to measurements of seating positions because that range is less sensitive to in-room speaker placement. Although a non-calibrated mic position may show HF roll-off, it won’t (shouldn’t) inlfuence waterfalls and spectrograms, it will just not look right ont he SLP charts.
4. Nonetheless, in order not to worry about the HF rolloff (seen on the charts but not present in reality) caused by non-calibration it’s advisable to load the relevant mic file into REW.
OK, not let’s take the UMM-6 mic with two response curves ( 0 and 90 dgerees) as an example and let’s have a closer look at this graph:
We can see that the lower end below 3-4 kHz is pretty much the same regardless of mic orientation, while the 0 degree curve (red) will need more compensation than the 90 degree curve (blue). (For the time being we may omit the 45 degree curve from our discussion.)
Here’s the table from CLS site for 0 degrees of the above chart with numbers:
Since the UMIK-1 usb mic is shipped with only 1 cal file for 0 degrees (on-axis) and more or less will show the same or similar characteristics on the occasion of being another Panasonic capsule type mic, my idea would be to modify the supplied table starting from 2.5 kHz and up by simply reducing the dB values by approx. 50%.
When done, the new figures can be copied/pasted into a notepad file which will be saved with a .txt extention. This .txt file will be the new cal file for the UMIK-1 for grazing incidence and can simply be loaded into REW. Job done.
Let me know what you think, please.