My research indicates that for room correction it is best to take room measurements with the mic pointed at the ceiling. Would the latest ECM8000 cal file posted in this sites download section be suitable for use with the mic pointed at the ceiling? I am thinking that the calibration labs might measure the mics on-axis, in which case this cal file might not be appropriate if I point the mic at the ceiling. Alphasmart Downloads.
I beleive the ECM8000 exhibits a different response on axis and at 90 degrees. Although with room measurements the sound is coming from all around so that is a very complex situation - can anyone shed some light on this? Also, is there much variation in the response of different ECM8000's? It may be an omni-directional mic, but the orientation definitely matters.
Chris Kyriakakis Founder and Chief Technology Officer at Audyssey Laboratories said that that they have done many tests with the ECM8000. I emailed him the latest ECM8000 cal file from this site and he asked him if he thought if would work for measurements taken with the mic pointing up and he made the following comments: 'It's hard to tell if this will work or not.
How was it measured? If it was done in an anechoic chamber and then inverted, it should be fine. But you need to ask if it is for free field (pointing to the speaker) or pressure field (pointing to the ceiling). The difference can be up to 8 dB at 20 kHz!!' So can anyone definitively answer the following questions about theECM8000 cal file available from this site (file name newecm.cal): 1) Is it designed for free field(mic pointing to at speaker) or pressure field(mic pointing at ceiling)?
2) Does this file represent the mics frequency response or is it an inversion? 3) Is there much frequency response variation between individual ECM8000's?
---------newecm.cal--------- 5.00 -24.79 6.30 -16.22 8.00 -12.54 10.00 -9.23 12.50 -6.64 16.00 -4.68 19.95 -3.09 25.12 -2.08 31.62 -1.30 39.81 -0.83 50.12 -0.41 63.10 -0.14 79.43 0.00 100.00 0.15 125.89 0.22 158.49 0.22 199.53 0.26 251.19 0.26 316.23 0.26 398.11 0.22 501.19 0.20 630.96 0.14 794.33 0.07 1000.000.00 1258.93-0.07 1584.89-0.13 1995.26-0.23 2511.89-0.27 3162.28-0.13 3981.07-0.22 5011.87-0.30 6309.57-0.25 7943.28-0.17 10000.00 -0.15 12589.25 -3.77 15848.93 -7.48 19952.6 -9.01 Cheers. Our calibration was professionally done. When using the ECM8000 it should be mounted upright. The file is the actual response of the microphone we had calibrated and not an inversion. We tested a few ECM8000's using this file and they were fairly close. If you wish to find out how West Caldwell Calibration Labs carried out their calibration, their contact information is included in the url I gave above. If you're concerned about accuracy beyond home use, then you should get your microphone calibrated.
We make no claims about the accuracy of the file we provide for download other than it is correct for the mic for which it was carried out. As a free service we provide this file for anyone to use with their ECM8000 knowing that it may not be absolutely accurate with their ECM8000. For home use, a movement of the mic element a few feet can easily result in several dB of level change, so it would be fine to use in a home theater. I think I need to get my ECM8000 calibrated.
I'm seeing some weirdness in plots for my speaker design and REW. For one, I seem to see an 8 to 10dB rise in the top octave (10k to 20k) in my responses that almost exactly mirrors the 'ideal' response file (newecm.cal). It's almost like my mic is flat and the cal file is artificially adding the 'peak'. I will run some sweeps horizontal and vertical with the mic and see if I can document the changes. I contacted Caldwell to see how much it would be for calibration. It might be worth it, as much as I use this thing.
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