Cheapest Calibrated Mic Ever

[oneoldude]

Parts Express sells its iMM-6 calibrated Mic for $16.25. But there is a catch. It is designed to be used on iPhones and Android phones, not on a PC. That prevents us from using our favorite PC software with the mic. So, it seems this is a perfect item to hack. That is what this thread is about.

Here are pics of the mic:

From the business end:

Image not available

And a profile:

Image not available

If anyone knows how to use this mic with a PC, please let us know.

I think that to make the best use of this mic requires hacking it. There are issues of course. Here are some. If you have more, please post.

One issue is that the plug is a TRRS (tip, ring, ring, sleeve) plug rather than a TRS (tip, ring, sleeve) plug as used in PC sound cards. So we need a schematic of what is going on inside the mic. I have been unable to find one. Anybody out there got the schematic?

Another issue is whether any phantom power is being delivered to the mic. PE claims it is a condenser mic. If so, power is required. This might be resolved with a schematic. Does anyone know details re: the phantom power issue and how to resolve it with a PC?

Another issue is the shape of the mic. I presume that the capsules are calibrated in their sub-carrier before the sub-carrier is placed in the frame holding the headphone/line out jack. So, the mic will be more closely calibrated with its curve if the jack and its related plastic is removed. Thoughts?

Another issue is whether the calibration curve was measured with 0 deg, 90 deg or 45 deg mic position relative to the sound source. My guess is it was done at 0 deg. Any ideas?

I think this hack would be a fun project and result in an impressive calibrated mic for very little cash.

What do you think?

[BobEllis]

Google is your friend for this, maybe not for all stuff.

[oneoldude]

Thanks, its a beginning.

[BobEllis]

http://www.digikey.com/scripts/dksearch/dksus.dll?pv69=367&FV=fff40016%2Cfff80517%2C4400043%2C8740005&k=3.5mm+jack&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

If that doesn't work, it's Digikey part CP-43514-ND

Connect the ring 2 and sleeve terminals to a 3.5 mm plug with shielded cable. All you need is a sound card mic input with a couple volts of phantom power - most do.

[oneoldude]

Thanks

[ttan98]

Hi,

Have anyone use this microphone for measuring freq. response of speakers since it comes with a calibration curve? Thanks.

[lhwidget]

Hi, you might want to hit this web site and explore a bit in their technical reports/info. iPhones have a nasty filter in their operating system to prevent overloading the mic's circuitry (I think). The mic may be calibrated to get around that as much as possible...

http://www.studiosixdigital.com/audiotools/

[ttan98]

Hi, you might want to hit this web site and explore a bit in their technical reports/info. iPhones have a nasty filter in their operating system to prevent overloading the mic's circuitry (I think). The mic may be calibrated to get around that as much as possible...

http://www.studiosixdigital.com/audiotools/

What I really want to use this hardware(microphone) with my speaker measuring software like Soundeasy and something similar, has anyone try this combo before to measure speakers frequency response.

[lhwidget]

I know, I was wondering the calibration tries to take the iPhone's wierd freq response into account. I hope you can get somewhere with this, I like the part, and the price

[lhwidget]

I see now. It looks like its actually calibrated flat.

http://www.daytonaudio.com/media/resources/390-810-dayton-audio-imm-6-user-manual.pdf

Neat.

I'll see if anyone at PE Techtalk has any ideas about the required phantom voltage. Once you know that, just parse the calibration file for your software, plug it into a good mic preamp with phantom power (I used a Rolls http://www.parts-express.com/pe/show...number=245-032). The Rolls has 48V phantom power.

[oneoldude]

If it is really a calibrated mic, it shouldl be calibrated to provide a flat frequency response for what it "hears" not what it might be plugged into. This mic may be used with a variety of equipment not just iPhones. The real question is whether the calibration thing is real or just marketing BS. If it is real, then another question raises it ugly head. If it is actually a real calibration, is it calibrated aiming at the sound source or at the ceiling?

If a mic is calibrated one way, then it is not calibrated the other way. So if it is calibrated for room measurement (aiming at the ceiling) then it will not read true for loudspeakers. And vers-a-vice-a. I asked at Parts Express and was told the mike is an omni and it makes no difference. Wanna bet? And if it is calibrated in between the two (at 45deg) then it won't be right for either.

The reason this mic is interesting is the opportunity to use it on a PC with real software like ARTA, REW etc. The first problem is the interface and the second problem is the prong that sticks out of it for earphones. It is in the way for making accurate HF measurements. See here: http://www.troelsgravesen.dk/measurements.htm So for the ultimate hack. Hack off the stub.

To solve the connection problem something like this should work very well: http://www.ebay.com/itm/Smartphone-H...item1e7607e631 But you better be sure what you are buying. Many ads are confusing and you may end up with something to plug PC ancillaries into an iPhone.

The nice part is for 17 bucks the mic might be worth the risk.

[lhwidget]

Good point, I've seen that, and some others. I recall one post where the author used a long cone shaped reflector (big end away from the mike's element). It helped a little bit. You're right, the "leg" probably needs to go.

I'm used to the EMM6 & 8 mics, which are calibrated on-axis. I suspect this on's the same. Doesnt it take a special element & geometry at the mic's element to work properly 90° off-axis?

[oneoldude]

I asked about it on another site and was told that if a mic is calibrated for a ceiling shot the direct shot would show a peak. The converse would also be true that if it is calibrated for a direct shot the ceiling shot would show a depression. I don't know of any inherent requirement of the design of a mic for one purpose or the other. But some mics are designed so they can sit on tables and couches for ceiling shots. I doubt it is an acoustical requirement and suspect they would be much better off away from boundaries.

BTW I agree with you. This mics capsule is probably calibrated off the mic for a direct shot and then installed in the contraption that holds it. It would be easier from a manufacturing standpoint. If the calibration is real at all.

[lhwidget]

Things are looking pretty good for your idea. Johnny Richards is doing the same thing on the PE board, and getting usable results. It seems like the mic is passive, no pre-amp like most measurement mics. The only problem might be a fairly short cable requirement to avoid noise & response problems.

http://techtalk.parts-express.com/showthread.php?237036-iMM-6-brief-review-(no-measurements)

http://techtalk.parts-express.com/showthread.php?237654-Dayton-iMM-6-measurement-progress&p=1912645#post1912645

He posted his calibration file in the second link. It's practically dead flat. I'm wondering, would a cal file for a celing shot show the hump you're referring to?

[pm709]

This thread is about a year old, but the following info should be useful for everyone:

First, according to Wikipedia;

"An electret microphone is a type of condenser microphone, which eliminates the need for a polarizing power supply (Phantom Power) by using a permanently charged material,
An electret is a stable dielectric material with a permanently embedded static electric charge (which, due to the high resistance and chemical stability of the material, will not decay for hundreds of years)".

I found a cheap way to connect to a Laptop Computer:

Radio Shack, $7.99 before taxes.. (click and zoom for details)..



The diagram on the back shows clearly headphones with microphone and TRRS connector..





I successfully measured and calibrated my room with this mic, and REW for Windows. Hope this help.