When I attended the meeting of the Nature Sounds Society in June 2014, I was able to see first-hand some of the exciting and effective stereo mic arrays made from tiny electret mics. Dan Dugan provided a variety of microphones from Telinga, which are based on Primo EM-23 or EM-172 capsules, and both sounded much quieter than the Audio Technica AT2022 microphone I had been using. After some research when I got home, with some helpful advice from Steve Sargeant (who occasionally makes a modified Jecklin array with EM-173 capsules available on Ebay), and I decided to take the plunge and attempt to make some myself.
I decided to stick with the EM-172 capsules due to their relatively inexpensive cost, low self-noise, and sensitivity. Their specs can be found here. These are the same capsules used by a number of nature recordists. It is important to note that they need 3-10 v power. My Sony PCM-M10 only supplies 2.5v (as do many of the small recorders). According to Steve Sargeant, the capsules work better with at least 5v of power, which results in lower input noise and greater dynamic range. But the capsules are still very impressive with only 2.5v.
I purchased a set of capsules and a kit from FEL Communications, and the necessary soldering gear (some links at the bottom of the page). The results were less than stellar, which I attributed to my limited skills in soldering. I also realized that the two most difficult parts of assembling the mics were soldering the plug and soldering the wires to the capsules. I decided to start over, this time ordering capsules from Frogloggers. These capsules came with wires attached (they are also available this way from FEL Communications). I bypassed the plug soldering by buying a “y” adapter RCA cable, which included a figure of 8 wire already attached to a plug. Below I go through steps I used to construct my mics.
Building the mics
Plus some basic soldering equipment:
Start by figuring out how long of a cable you want, and snipping off the RCA plugs at that length. Split the two wires at least 6 inches. Strip about 1/2” from each end.
Carefully separate the ground wire from the insulated signal wire. Twist both tightly.
Tin each wire with solder. Strip about 1/4” to 1/2” of insulation from each of the wires attached to the capsule. Note that the wires are thin and fragile – handle with care. The wires are probably already tinned, but if not, tin them, too.
Bend each wire into a tight hook. BEFORE you do this, make sure you have the heat shrink in place! You’ll want heat shrink for each connection, plus a larger piece to cover the whole thing. If you are going to slide the capsule inside a holder, you might also need to get that on the wire before soldering as well.
Place the wires from the cable and the capsule in the helping hands, and carefully hook the ends of the red to red (or white) and black to ground wires together.
Carefully solder the wires together. Do a better job than I did.
Slide the heat shrink over the connections. The ground wire CANNOT touch the hot wire or it will short. If you have problems with the heat shrink covering everything, try using some Liquid Tape (see below) to cover any exposed wire.
If you are going to use the mics as binaural mics, make sure the heat shrink includes the base of the capsule, overlapping the sides, and you’re done. If you are going to seal the capsules inside a holder, then the heat shrink as pictured is ok.
Last step, seal the mics inside the holder. This can be done with hot glue, but you have to be very careful of the temperature as the capsules are really sensitive to heat. Better is a silicone sealant like Permatex RTV sealant (see below). Be very careful to not get any sealant on the front of the capsule. You might want to cover the front with a small piece of electrical tape when sealing.
I placed the capsules inside the caps from Sharpie® permanent markers. I snipped off the end below the clip and fed the wire (before bending or soldering) through the hole. I used the “fine” markers, but the “ultrafine” will also work. I used Permatex RTV to seal the capsules inside the caps. The arrangement has worked quite well, and has resulted in capsule that I can use as tree ears, with a Jecklin disk, and in a spaced array. And the clip could also be used to fasten to the front of a button-up shirt so the mics could be used as lavaliers (better in a mono setup, though).
The mics could also be mounted in a variety of other materials.
Using them in the field
To use the mics outside, they need some form of wind protection. I used foam (insulating foam for air conditioners, available at hardware stores) with a cut-out for the capsule and rounded off, and covered that with a thin layer of acoustic foam. I covered the whole thing with faux fur. I attached Velcro to the bottom of the fur to reduce wind coming in the bottom.
To use the mics for soundscape recording, I usually use them in “tree ears”fashion, by wrapping a cord around a tree 6-8 inches in diameter. I use wooden clothespins to secure the fur-covered mics to the cord. I have a small camera case that my Sony PCM-M10 fits in; it has a strap to slide over a belt, so I use that to hang the camera case with the recorder on the cord also.
Equipment and supplies
Here are some links to the supplies I used, or reasonable substitutes. Note that the cables are relatively cheap. I consider these “testing” cables. I will likely make another set of mics in the future using higher quality cables with better connectors.
Belkin Audio Y Cable Splitter 1-Mini Plug, 2-RCA Plugs (6 feet)
URBEST®180 pcs Heat Shrink Wire Wrap Cable Sleeve Tubing Sets Assorted Size
Kester Pocket Pack Solder 60/40 0.031 0.50 oz. Tube
SE MZ101B Helping Hand with Magnifying Glass
Some optional supplies/equipment that make things easier:
Solder Sucker- desoldering pump
Eclipse 902-109 5″ Diameter Magnifier Workbench Lamp with Bench Clamp, White
Permatex 80050 Clear RTV Silicone Adhesive Sealant, 3 oz.
Gardner Bender LTB-400 4-Ounce Black Liquid Electrical Tape
Using with phantom power instead of PIP
There was some discussion last year on the Micbuilders Yahoo Forum as to how to optimize the power for the EM-172 capsules, which appear to do even better at higher voltages than small recorders can supply via PIP. If 12v or 48v power is available, here are some instructions to create an XLR version of the EM-172s. Tom Benedict has created a great tutorial on building the mics for phantom power.
For more information about building the mics, including illustrations of other builds and some soldering instructions, check out the following links:
Also check out the Micbuilders Yahoo forum (search for EM 172); there is a lot of information there. And please share your experiences. There are many ways these capsules can be put together and used, and we could all learn from other experiences.
Last modified June 2016.