DIY measurement mic

[Shaun]

Originally posted by Helmuth
This i use with my behringer emc8000

I'd like to also share my mic circuit; very similar. I have gerber files for anyone who wants to build it.

http://www.elipse.co.za/Images/MicBehr.pdf

[DonA]

Like many here, I looked for a cheap solution to the problem of a reliable, accurate measurement mike. I was frustrated with small but still (to me) significant differences in results with different budget mikes. Eventually, I purchased an ACO Pacific PS9200/4012/7012 calibrated mike system. And you would think that would be the end of it, however, some observations eventually forced me to send the system out to be directly calibrated against not one, but two B&K calibration mikes and I am now absolutely convinced of the reliability and accuracy of my measurements. My whole purpose for relating this story is to show how difficult it can be to get 1 dB or tighter accuracy. However, as discussed above, with various budget mikes, you can still achieve USEFUL results above 2 to 3 kHz which will still serve you very well and will still be fairly accurate over a couple of dB. I think the cheapest way to accuracy is to find someone to calibrate your mike for you against a known reference. In this way, a budget mike can produce quite accurate measurements. Unless you have a friend to do it for you, expect to pay for it. I know everyone is looking for an easy and inexpensive answer. My solution cost me about US$2000 but I have absolute confidence in my measurements. Like an old friend once said... Buy the good stuff... It only hurts once... ;>)

One more thing... We haven't covered the issue of the reliability of distortion measurements and this may not be the thread to do it in, but there are MANY things to watch out for there before you can believe what you measure.

[ente]

... some stuff more:

http://www.fesb.hr/~mateljan/arta/Ap...r-Rev03Eng.pdf

and this (page 15 ff)
http://www.ctc-dr-weber.de/speaker/A...re%20First.pdf

Regards
Heinrich

[askbojesen]

Hi, if of any interest I have a calibration file for the Panasonic wm-61a.

The capsules differ a few dB and degrees in phase.
But in overall they are quite the same

http://www.holmacoustics.com/downloa.../Mic_WM61A.cal

The attached image show 3 capsules (The dashed lines are the phase)

[infinia]

Originally posted by askbojesen
The capsules differ a few dB and degrees in phase.
But in overall they are quite the same

Hi
Yes, very interesting (for unit to unit variation) quite good, but expected from same/similar batches.

Any information of the test configuration would be very much appreciated? In other words ...Can it be repeated by DIY folks here?

TIA

[PLB]

Hi Thadman,

Sorry for the late response to this topic, but since I'm a relatively new member, I ran into problems with the attached file size and had to ask for help from one of the moderators.
I wanted to warn you about my findings on the Behringer ECM8000 that I recently purchased. I had checked out Behringer’s web site for the spec’s on this mic prior to purchase and it seemed OK. However, when I received it, I found the attached printed on the outer cardboard sleeve that covered the carrying case. As you can see, there is a significant rise in the response at low frequencies due to proximity effects, making it quite unusable as a measurement microphone at these frequencies. I haven’t had the chance yet to construct a phantom power supply for this mic, so I don’t know if this response truly represents the response of this particular ECM8000 sample. I’ve sent an email to Behringer about a week ago asking them to elaborate on the applicability of these curves to the ECM8000, but I haven’t received a reply yet. I’m hoping it isn’t going to be a problem, and that the response will be the same as what Behringer advertise on their web site. I will probably have a phantom power supply up and running in a week or so and will let you know my findings. If anybody else has checked for proximity effect on this microphone I’d appreciate them letting us all know their results.

Peter

[Shaun]

My guess would be that in order for the object to affect the mic response (proximity effect) it has to be of a size comparable to the wavelength at that frequency. Note also how quickly the effect drops away with distance.

This is just my opinion, of course.... the usual caveats apply.

[Ron E]

I wonder if that is a printing error.

"Proximity effect" is an issue with directional microphones. Omni mics should have no proximity effect.

[cuibono]

Yeah, an omni mic doesn't have proximity effect - but that doesn't mean the Behringer doesn't have a bump in the low end. Anyone in the US should pay $40 for a calibration, its sooo worth it. See my post earlier in this thread.

[Thawach]

cuibono, i think all mics to have proximity effect at low frequency. some mic has much proximity effect. some has less.