DIY Mic “EMR 10MH” induction microphone (#666.013)

Introduction

The “10mH” is NOT a microphone for sound.

Well, it is and isn’t. Instead of a microphone capsule that captures sound waves, like our first DIY microphone build, this uses an inductor that captures electromagnetic waves, and all in the same tiny format as the previous microphone. So, you can make all the noise you want, sneeze, cough, it will not pick up your disgusting human sounds because those are all sound waves, not electromagnetic waves. Though, if robots ever had a reason to cough, this microphone could pick that up…

This little guy will make an awesome experimental soundscape induction microphone for probing electronics, circuits, etc, as it’s super sensitive and super compact.

Name: Our first DIY microphone (codename Purp) has been dubbed the “5024” after its capsule’s model name. This one (the white ones in the header picture) will be the “10MH” for the inductance rating, measured in Henry, millihenry in this case, or mH, of the inductor.

Sounds examples

Assembly, reasoning

The assembly is largely the same as our first DIY mic, so I’ll leave that guide here:
https://emirizzi.com/blog/666002-diy-mic

The only difference in this circuit is the inductor instead of the AOM-5024L-HD-R electret microphone capsule. Like this diagram shows. (made with free CircuitLab.com)

This specific inductor was chosen for it’s high sensitivity (Henry rating), very low price and small enough size that it could fit into the end of an XLR connector to keep with the compact nature of these line of microphones.

The same filtering circuit was used as in the 5024, as it proved perfectly acceptable for recording electromagnetic interference.

I originally sourced my inductors from Amazon which I’ve started boycotting for many reasons. I’ve sourced an alternative 10mH inductor in the same format HERE or an even more sensitive one HERE, which I couldn’t find at the time of making this.

Frequency Response of the 10MH

Again, it’s very important to note that this is NOT a microphone for sound waves.

The frequency response is shockingly uneven, but that’s because it’s picking up the electromagnetic waves of the circuitry (including the magnetic interference from the speaker magnet) BEHIND the Kali LP-6 monitor I used to test this. This was more for fun, to see what would happen.

This terrible frequency response gives me the inspiration to finish my variable resistance/capacitor project, so I can fine tune the LPF circuitry in this 10MH microphone, because that -50dB drop-off from 1.5-2kHz could be improved, if (big if) it’s caused be the current circuit. TBC… Thanks for reading :)