So I've been on the lookout for an affordable, small diaphragm/body omni mic for room measurements. Something that will be be more omni to a higher frequency than a 1/2" mic body. I've had my eye on the MicW M416 for that purpose for some time, but last month I saw that Behringer sells a new measurement mic that looked like it would fit what I was looking for so I took a chance and ordered one.
It's called the ECM PRO, and it's clearly "inspired" by the DPA 4091, or Neumann MA 1. But as of this writing, it is only about $40. There is a calibration file that you can download for it that is highly suspect. I tested it out against one of my calibrated ECM8000's with a tweeter in a low(ish) diffraction cabinet, IR windowed, and trying to get the diaphragms in close to the same point in space.
Here is on axis ECM PRO uncalibrated and ECM8000 calibrated:
Here is ECM PRO 0 degrees to source and 90 degrees to source:
And for comparison, that ECM8000 also at 0 and 90:
I haven't tested it at low frequency yet, but the ECM PRO is as expected, more omni than a ECM8000. Unexpectedly, however, this particular one needs only minimal calibration.
It's called the ECM PRO, and it's clearly "inspired" by the DPA 4091, or Neumann MA 1. But as of this writing, it is only about $40. There is a calibration file that you can download for it that is highly suspect. I tested it out against one of my calibrated ECM8000's with a tweeter in a low(ish) diffraction cabinet, IR windowed, and trying to get the diaphragms in close to the same point in space.
Here is on axis ECM PRO uncalibrated and ECM8000 calibrated:
Here is ECM PRO 0 degrees to source and 90 degrees to source:
And for comparison, that ECM8000 also at 0 and 90:
I haven't tested it at low frequency yet, but the ECM PRO is as expected, more omni than a ECM8000. Unexpectedly, however, this particular one needs only minimal calibration.
I am also curious about that. One would like to imagine that because of the small diaphragm it would be able to take higher SPL... but we'll see. I'd also like too see what its noise floor looks like.
Certainly has some requirements that might make it be capable of measurement
Compared to DPA 4091…
Smaller diaphragm/capsule head > more extended FR ☑️
Lower sensitivity > higher SPL capability ☑️
One missing stat is self noise… but with a longer sweep and/or coherent averaging in REW, you might just be able to measure down to your room’s noise floor…
Thoughts @IamJF
?
Impressive 3 year warranty.
Edit: Found it!
Move over Sonarworks Sound ID…
Compared to DPA 4091…
Smaller diaphragm/capsule head > more extended FR ☑️
Lower sensitivity > higher SPL capability ☑️
One missing stat is self noise… but with a longer sweep and/or coherent averaging in REW, you might just be able to measure down to your room’s noise floor…
Thoughts @IamJF
?
Impressive 3 year warranty.
Edit: Found it!
Move over Sonarworks Sound ID…
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Dear Jürgen,
It looks like a generic one, as I managed to download the calibration file (which is a .rar archive) without entering any codes.
Do you have any time in your busy schedule to measure it for the diyAudio community?
If so, I will attempt to have it shipped to you.
Once testing is done, it can be added to the low distortion microphone compilation
It looks like a generic one, as I managed to download the calibration file (which is a .rar archive) without entering any codes.
Do you have any time in your busy schedule to measure it for the diyAudio community?
If so, I will attempt to have it shipped to you.
Once testing is done, it can be added to the low distortion microphone compilation
Hey @tktran303
I'm busy at the moment but will be able to take time over the Christmas days. Let's check how we can manage this!
As noise is not specified I'm afraid it will be pretty high with the small capsule. But there are chances that it is also more stable ... we need to test a dozen over a few years to be sure 🤓
I'm busy at the moment but will be able to take time over the Christmas days. Let's check how we can manage this!
As noise is not specified I'm afraid it will be pretty high with the small capsule. But there are chances that it is also more stable ... we need to test a dozen over a few years to be sure 🤓
this one cannot be used in a piston calibrator with standard diameter mikes.
It's just a generic one, which is kind of funny because the mic has a serial number. But given how closely (and smoothly!) the calibrated ECM8000 and my ECM PRO track, the cal file Behringer provides looks mighty questionable to me.
Yes. I'm a bit disappointed that they didn't go with a standard 1/4" body, maybe a 3D printed adaptor?
I used the behringer case to build my own mike using the `panasonic 61 capsule. Ffter modifying the capsule to sourcefollower mode and bootstrapping the gate drain cap away, the sensitivity of 2 units built was less than 0.2dB different. Max SPL was well over 145dB due to the large signal swing possible.
@IamJF as we await your availability to test the ECM PRO, I can attempt to do some distortion and noise tests on the unit I have and we might be able to see how consistency is... or how bad I am at making a test fixture. Please let me know if you have any advice for doing distortion and self noise testing. My biggest question is setting gain between microphones.
What soft/hardware do you use for testing?
We need some kind of calibration for the mic - that's actually not easy with no standard shape! The front volume in the claibrator is normally exactly dimensioned to fit the diameter, it's nit just to reduce the hole. So chances are high you are off when printing SOME adapter. There also must be a good sealing, not easy with that shape.
Alternative is to reference with a speaker and a known microphone. Kalibrate your RefMic with calibrator, calibrate your speaker for 94dBSpl, use your DUT and calibrate for 94dBSpl. Not as exact as a direct calibration and WAY more effort but probably the only methode for now.
Distortion tests, you need a pressure chamber. And it strongly depends of the frequency range you need to measure - low frequencies are easy, up to 300-500Hz is still easy, 1kHz get's more interesting, 10-20kHz is VERY hard to do.
In short you need a speaker with rubber surround and air tight membrane. Then just mount it air tight to a wooden board and use the volume in front of the membrane as pressure chamber. Drill a hole and put your mic through, seal it up.
You get extreme SPL levels with very small membrane movements that way. But you need to check/calibrate the setup with a known ref mic before you measure other mics.
I use REW for software, a couple different USB interfaces (Behringer UM2 is what I use frequently but I also have a UMC204HD), a Quest QC-10 calibrator, a collection of SPL meters, and a pair of calibrated ECM8000's. I also have a NTi Audio M2010 if a better mic is needed.
I've used that method before I had my calibrators, so I'm comfortable enough with it.
I know the gain should be low enough to have the necessary headroom, but if I'm going to compare an ECM PRO with a ECM8000, when I switch between mics, should the mic gain be changed on the interface, or should I just tell the software that it's hearing 94dB for both of them?
The only speaker I have sitting around has a foam surround, so I'll have to get one with rubber. I assume that speaker quality is of minimal importance? I'm only interested in below 500Hz at this point.
Thanks for your help!
Without having to build anything new, what about the microphone in a box method?
https://audioxpress.com/article/measuring-loudspeaker-low-frequency-response
It's not new, having been described by Richard Small in 1971 as a way to measure the bass response of speaker. It's an earlier technique, as opposed to the Keele's near field technique, the ground plane technique and certainly the Klippel Near Field Scanner. Someone interested in radio/speaker/microphone history can fill us in, I'd be fascinated as to why out of favor. But I've used the idea of alternatives eg. measuring box resonances.
Anyway I digress, the SPL inside the box is quite high, as demonstrated in the article. It would be a quick and dirty assessment to see if indeed the ECM Pro is lower in distortion and/or self noise than the ECM8000. It would be even a bonus if it was better than the NTI M2010, but we might not be ready to take the red pill just yet.
So you could an existing speaker you already have (ported would be ideal, as you won't have to drill a hole in your nice cabinets. As you have an SPL calibrator, you could calibrate absolute SPL with one of the mics.
Then play the speaker that various SPL steps in REW, without much effort from the speaker itself. eg. 90dB/1m, the SPL inside the cabinet will be well in excess of 115dB... For frequency between 20-200HZ, as long as you keep the microphones in the same place, you can do a comparative assessment. Don't forget to seal up the port with a few socks or two.
<disclaimer> I haven't tried this yet. Just another one to add of the list of empirical tests to try. As usual, please test with low SPL, protect your mics, and wear ear muffs- protect your ears!
https://audioxpress.com/article/measuring-loudspeaker-low-frequency-response
It's not new, having been described by Richard Small in 1971 as a way to measure the bass response of speaker. It's an earlier technique, as opposed to the Keele's near field technique, the ground plane technique and certainly the Klippel Near Field Scanner. Someone interested in radio/speaker/microphone history can fill us in, I'd be fascinated as to why out of favor. But I've used the idea of alternatives eg. measuring box resonances.
Anyway I digress, the SPL inside the box is quite high, as demonstrated in the article. It would be a quick and dirty assessment to see if indeed the ECM Pro is lower in distortion and/or self noise than the ECM8000. It would be even a bonus if it was better than the NTI M2010, but we might not be ready to take the red pill just yet.
So you could an existing speaker you already have (ported would be ideal, as you won't have to drill a hole in your nice cabinets. As you have an SPL calibrator, you could calibrate absolute SPL with one of the mics.
Then play the speaker that various SPL steps in REW, without much effort from the speaker itself. eg. 90dB/1m, the SPL inside the cabinet will be well in excess of 115dB... For frequency between 20-200HZ, as long as you keep the microphones in the same place, you can do a comparative assessment. Don't forget to seal up the port with a few socks or two.
<disclaimer> I haven't tried this yet. Just another one to add of the list of empirical tests to try. As usual, please test with low SPL, protect your mics, and wear ear muffs- protect your ears!
That's a good suggestion, I even have a pair of ported speakers I can use. There's supposed to be a driver with a rubber surround arriving at my house in a couple days, so I'll be able to compare the MiaB method to a dedicated test chamber too.