Typically this requires the use of two mics: one to pick up the middle (this is usually omnidirectional or cardioid) and one to pick up the ambience from the sides (that has to be a figure-8 mic). In the studio these are typically high end condenser microphones or ribbon microphones. The basic gist of this technique is that you have a “Mid” microphone pointing directly at the sound source you want to record and a “Side” microphone that faces to either side of the source. Then in mixdown you can do a little shuffling of the side signal and can get a very nice stereo image. The other key benefit is that is collapses into mono without any artifacts or phase nuances. I originally designed and built one of these in the 1990's using little panasonic WM60 capsules. I wrote it up as a DIY article in Recording Magazine and released it as a kit with PAiA electronics.
At the time I was really impressed with how well this worked with inexpensive capsules and top quality opamps. It wasn't quite on par with studio mics but it was a really great project for its day. A couple decades later many things have changed. My skills as a designer and understanding of analog electronics are better. The availability of parts has improved, specifically microphone capsules. And finally, digital recording software has become ubiquitous – even open source software. It was time to revisit building an MS microphone!
Based on my previous instructable I already had the building blocks needed for this project. The “Aha Moment” came when I built four identical microphones and one was out of phase with the other three. Since I built them at the same time this one really bothered me. Could it be the capsules had poor quality control? It wasn't until I disassembled the microphones that I found I had wired the capsule backwards in the errant microphone. I had wired the ground to the center pin and the input to the FET to the case of the capsule. Because the capsule was in a plastic holder and insulated, the only thing that happened was reversing the phase of the signal compared to the other three microphones. This lead me to pondering and thinking... What if I wired two capsules in series with one set of electronics? Would it work? If so, I could face the capsules front to back and create a figure eight pattern. And sure enough, it does work. Now, if I could fit those two capsules into one case with a third capsule facing front, I had the makings of a complete MS mic in one body. I also needed two circuits in the case and the ability to bring both signals out of the microphone at the same time and I was all set. This required a smaller capsule than the TSB2555B that was in my other microphones. The same company makes one called the TSB-165. It is pretty renown in the mic building community and is the one used in the “Alice” microphone that originally got me started with building my own microphones.
So I ordered another BM-800 microphone from Amazon, fired up my soldering iron and turned the idea into reality. In honor of Scott and his design, I am naming this microphone the “MS-Alice”.
Here is what you will need to build this project:
Three TSB-165 capsules
One BM-800 donor body: Go to amazon or ebay and search “BM-800” then sort on price.
One five Pin Male XLR
One five Pin Female XLR
Two male three Pin XLR cable mount connectors
30-40 feet of Mogami balanced small microphone cable
Two sets of electronics from the original instructable
a small portion of 1/2” PVC pipe for the microphone capsule holders.
Assorted hand tools, soldering iron, hot glue gun (of course, this is an instructable) and hook up wire.
UPDATE** I added two audio files. One with this mic and the other with a pair of my TSB2555B mics in ORTF layout (spaced about 8 inches apart angles about 110 degrees.) edited 5 Oct 2016.
Disassemble the BM-800 donor body. The three bodies in the picture show you the variations in what you get. But for the price, I am not complaining!
Remove the PC board, the top section (head basket), the XLR connector, and break it down completely. Keep all the little screws, you will need them. We are only using the mechanical housing. It still blows me away that you can buy one of these for under $20. You can not build the equivalent for anywhere near the same price.