DIY measurement mic

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#22
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.
 
#24

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#25
Re: Panasonic wm-61a Calibration (Gain + Phase)

askbojesen said:
The capsules differ a few dB and degrees in phase.
But in overall they are quite the same
Click to expand...


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
 
#26
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
 

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#27
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.
 
#29
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.
 
#31
Re: Re: Panasonic wm-61a Calibration (Gain + Phase)

infinia said:

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
Click to expand...

The microphone capsules have been calibrated in cooperation with
the danish company (http://www.delta.dk )

It is the on-axis response.

My point is that if anybody are using a WM-61A without any clue about the response and have no calibration, then the calibration I link to is a lot better than nothing.
http://www.holmacoustics.com/downloads/MicrophoneCalibration/Mic_WM61A.cal

The measurement program I use is freeware (Developed by me): HOLMImpulse
(I might start a new thread about this program if of any interest)
 
#32
The measurement program I use is freeware (Developed by me): HOLMImpulse (I might start a new thread about this program if of any interest)
Click to expand...

askbojesen,thanks to tell everyone , its interesting software. i download and try it a little(still don't know how to use) but ill tell my friends about this free software.
 
#33
Can anyone who's built a measurement mic from the wm-61a capsule provide a little clarification for me?

I've been trying to get this to work, but I've read all sorts of different reports on exactly HOW. Most of the tutorials I've read state that these microphones can simply be wired up to a standard connector and directly connected to a computer sound card with no problem. I have had no luck doing so. Other people say you need a pre-amp, but my sound card technically IS a pre-amp, and that's not helping me at all either, though I'm not entirely sure if I'm using it properly as it applies to this microphone.

I'm using a creative labs E-MU "Tracker-pre," which is similar to the 0404 with some slilghtly expanded capabilities, like direct monitor and inserts.

I've wired a microphone to a standard 1/4" mono connector and connected it to one of the inputs, and even with the gain turned all the way up, the the microphone registers almost nothing. If I blow directly into the microphone I can see the levels rise a little bit.

I'm not entirely sure what the best route to go is. The pre-amp does do 48v phantom power, but I haven't found a good explanation of how to get that to work with the wm-61a.

I'm rather flustered at the moment and would really appreciate some encouraging info!
 
#35
I built a pre-amp for mine.
Click to expand...

this is what I'm using:
http://www.emu.com/products/product.asp?product=17511

Would that not be considered a pre-amp, for the purposes of this microphone?

"The Tracker Pre USB provides users with two Class-A ultra-low noise Mic/Line/Hi-Z preamplifiers that can be run independently or in stereo..."

Yet, plugged into one of these inputs, with the gain completely cranked, I get nearly no noise.

I thought at first I had perhaps damaged the capsule during soldering, but I've done 3 now and they all perform the same. Resistance of the microphone is measured at ~700ohms both before and after soldering on all 3 attempts.
 
#37
You need to polarize the capsule with a voltage.
Click to expand...

Okay, looks like I'm just going to go that route, then.


I'm still curious though, as there are a number of tutorials out there that specifically talk about wiring these directly to a connector and connecting them directly to your soundcard or something like a minidisc recorder, and make no mention of any sort of pre-amp.

Perhaps these devices do provide some small amount of voltage for that purpose?

Anyway, looks like I've got to make a run to radioshack!
 
#38
tresch said:
I'm still curious though, as there are a number of tutorials out there that specifically talk about wiring these directly to a connector and connecting them directly to your soundcard or something like a minidisc recorder, and make no mention of any sort of pre-amp.
Click to expand...

See the diagram in this Binaural Microphone Construction article. Some minidisc players do provide this or similar circuit so you can, indeed, just connect up the capsule. I have read the same. But not all have this feature.

The 48V phantom power your card supplies is not the same, though. It is used to power mics like the Behringer ECM8000 that have their own built-in preamps. I suspect that applying the 48V directly to the Panasonic capsule will blow the internal FET.
 
#39
tresch said:


Okay, looks like I'm just going to go that route, then.


I'm still curious though, as there are a number of tutorials out there that specifically talk about wiring these directly to a connector and connecting them directly to your soundcard or something like a minidisc recorder, and make no mention of any sort of pre-amp.

Perhaps these devices do provide some small amount of voltage for that purpose?

Anyway, looks like I've got to make a run to radioshack!
Click to expand...


There is a minijack input at the back of the Tracker. It provides adequate bias voltage for electrets (+5V) and it works. Don't make anything additional. Just use that input. I know it for sure bcs I have a Tracker Pre and electret measurement calibrated mics.
 
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