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Discussion Starter · #41 ·
You may be right Mike. That's the only thing that I can figure is that the larger airspace, the vent and the much different impedence curve caused it. I never did investigate it more. Not enough time in the day you know?

I've found out a lot of things that make me doubt some of these measurements anyway. The fact that the ECM8000 has increasing distortion the lower the frequencies involved get and at levels above 110db as reported by Herb at Cross Spectrum Labs so the THD results are probably jacked. The variation in the bunch of ECM's that he has tested is also around 6db at both ends of the spectrum. I also recently found out that my CM140 SPL meter needs calibrated and reads a bit over 3db too low :doh:. This is what I calibrated my ECM8000 and REW levels to, so they are all lower than they should be.

I do have a calibrated ECM now and a 2nd CM140 which reads about 3db higher than the old one. I'm planning on sending the 2 CM140's plus my other ECM8000 to be professionally calibrated too. Interestingly there is quite a bit of variation between the 2 ECM8000's too. One is noticeably less sensitive than the other.
 

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I read about the variation on the ECM 8000's a while ago, and I am thinking of getting a calibrated one as well. The only SPL meter I have is a Rat shack analog meter, and it's obviously bunk, I don't know if someone else dropped it when it was borrowed or not. :explode:

I'd probably pick up a Galaxy CM140 as well as a WT3 so I can do my own tests of impedance in box.
 

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Discussion Starter · #43 ·
It's probably worthwhile with as much time as you spend messing with this junk. It's easier to just order a new ECM8000 pre calibrated from Herb, once you factor in shipping and the calibration costs to send your current mic in it's a difference of $25 or something like that. That's what I did. Plus you end up with another mic as a back up.
 
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