Camera Mount ORTF Stereo Microphone

One of the cooler stereo microphone techniques out there is ORTF or Office de Radiodiffusion Télévision Française. Named for the French office of Radio and Television. What I like it because it sounds really good and, is simple to implement. All you need are two cardioid microphone capsules spaced 17cm apart that point 110 degrees away from each other. There is no encoding or decoding like MS or even my own Ambisonic mic. I recently started using a really great 16mm electret capsule from JLI electronics. It is the baby brother to the TSB2590. I’ve also been experimenting with easy to do wind reduction methods. By combining all of this, I came up with a very simple rig that can connect directly to a camera or recorder that has a stereo 3.5mm input jack. It is small enough to mount directly to a camera with either a ¼-20 screw or a cold shoe mount. The stereo spread works amazingly well when on camera too!

Here is what we will need:

Two mic capsules: https://www.jlielectronics.com/microphone-capsules/jli-160a11uc680/

3.5mm stereo jack: https://www.redco.com/Rean-Neutrik-NYS231BG.html

2-3 ft of shielded lavalier mic cable: https://www.redco.com/Mogami-W2368.html

Hair Curlers: https://www.amazon.com/dp/B07K7958W8

Fake Fur (See Text) 

Sheer Nylon Fabric (See Text)

¼ inch thick wood (Oak or other)

https://www.lowes.com/pd/Common-1-4-in-x-3-in-x-4-ft-Actual-0-25-in-x-2-5-in-x-4-ft-Oak-Board/1000018163

Misc mounting hardware:

Male-Female adapter with thumbscrew mount

https://www.amazon.com/Release-Adapter-Washers-Thumbscrew-Mounting/dp/B09NR5XJ8W/

Cold Shoe 1/4-20 adapter https://www.amazon.com/Camera-Mount-Tripod-Screw-Adapter/dp/B018UJLIOE/

Barrel Nut

https://www.amazon.com/ChromLives-Tripod-Connection-Articulating-Replacement/dp/B08J86P99C/

Red Barrel Nut (They are nice but shorter)

https://www.amazon.com/CAMVATE-Female-Thumb-Adapter-Pieces/dp/B06XYDT8TY/

Another ¼-20 male female adapter – with rubber grommet. 

https://www.amazon.com/Release-Adapter-Thumbscrew-Mounting-Frgyee/dp/B096FG59D2/

Rubber washers: (These aren't necessary but super helpful)

https://www.amazon.com/gp/product/B07GCSQNXB/

This is really important for microphones used outdoors. They are commercially available for specific microphones but not this one. Commonly known as “dead cats”, they consist of a layer of thin fabric and a layer of fake fur mounted on a frame to hold them away from the microphone element. They need a bit of airspace to work effectively. I figured, why not just permanently  mount them to the mic frame? Makes it easy in the long run and actually simplifies construction. I found a set of hair curlers on Amazon that fit the bill perfectly for working as the frame portion. They have a  ⅞”  inner diameter. So making the mic holder part ⅞” thick lets it slide right into one of the hair curlers. A little hot glue and the cloth and fake fur become one with the  hair curler. Voila! Instant custom “dead cat”. These work really well with other small capsules on their own too.

The first step is to make the frame for the mics. ORTF is based on having the capsules spaced 17cm apart and angled 110 degrees from each other. So, one points 55 degrees and the other -55 degrees. I designed a holder that can be cutout of ¼” wood by hand or laser cut. You can even 3D print one. Files for both are included. The laser cut one is my preference. The .svg file needs to brought into lightburn or other program and setup for the particular laser. I am a member of the Dallas Makerspace, which makes that part easy. The design is a ⅞” wide, so it fits the hair curlers we are using for wind protection. It is 23 cm long. 17cm plus the length of a hair curler. That allows for centering the capsules in the hair curlers. We also need a hole for the ¼-20 mounting hardware right in the middle. The capsule mounts are 16mm in diameter to match the capsules and then there are two cutouts 16mm wide that angle out 55 degrees and -55 degrees. This makes the capsules point 110 degrees apart and gives some space behind the capsules to make sure that their cardioid response is not affected. Pretty simple. You can see my design progression in the below figure. All done in Inkscape

The capsules we are using have an internal Field Effect Transistor (FET) allowing us to interface with it simply. Literally all we need to do is connect some wires. The capsule is known as a “Three wire” as the Source (S) and Drain (D) connections to the FET are brought out along with Ground (G). Two wire connections the FET source is connected to ground internally. We will make that connection externally. 

Wiring the capsules consists of connecting the capsules (one for right, one for left) to a 3.5MM stereo jack. The capsule side uses the shield wire twisted together and tinned to connect the “S” and “G” terminals. Then the center conductor is soldered to the “D” connection. See diagram below. Normally Right is “Ring” and Left is “Tip” but don't worry about tracking it as you solder. We will figure out later which is which. Here is the sequence of construction:

1. Cut two lengths of the shielded Mogami W2638 wire about 16 inches long
2. Strip the shield back about ½”
3. Twist the shield and tin with solder
4. Strip just a bit of the center conductor
5. Tin the center conductor
6. Solder the shield portion to connect the S and G connections
7. Solder the center conductor to the D connection
8. Repeat for the second capsule
9. Feed both the unstripped ends through the connector shell AND the insulator sleeve 
10. Now strip back about ½” of the shield insulation
11. Twist the shield back but to not tin the shields
12. Strip just a bit of the center conductors back
13. Tin the center conductors
14.  Tin the Tip and Ring connections on the 3.5mm jack
15. Solder the center conductors to the Tip and Ring
16. Fold the shields back across the ground connection on the 3.5mm jack
17. Solder the shields to the jack connection
18. Cut any excess shield that sticks out from the ground connection
19. Inspect your work
20. Using needle nose pliers, crimp down the ground connection to allow the connector shell and sleeve to slide over the 3.5mm jack  
21. Slide the plastic sleeve over the connector
22. Slide the shell over the connector and screw down 

Test this before doing anything else! Connect this to a PIP input stereo recorder or camera and either listen live with headphones or record a short snippet while talking into each mic capsule. Listen to make sure they both work.

Now that you know they work, (or found your wiring issue) let's glue them to the holder. We are using E6000 glue as it is both easy to work with, and can be pulled apart if needed.

The easiest way I found is to use a couple coins, wooden stir sticks or something similar to elevate the holder piece up off the work surface.  THen fit in the capsules so they stay in place without moving. Then put a dab of the E6000 on either side where the capsule esde meets the frame.  When the glue dries in an hour or two, flip the holder over and apply two small dabs of glue to the capsule/holder joint on the now exposed side. Let the whole assembly dry overnight.

Now on to the wind protection. To me, this is one of the things that separates this from “just a microphone” project. All we need are two plastic hair curlers, some light cloth and some fake fur. I got both of those from my local Hobby Lobby but Joann's fabric carries both as well. Check out their website and search faux fur. You want fur that is 1.5-2” long and the light fabric to be pretty shear. Nylon or thin dress lining stuff.  This combination is what most manufacturers use. I actually got the idea from a Rycote DIY wind jammer kit that was basically a piece of red nylon cloth and some black fake fur. And, the kit costs more than a yard of fur at a fabric store. 

Note on Cutting Fur! The hairs will get everywhere. There are a couple things you can do. After cutting into the smaller pieces we need, you can throw the section in a clothes dryer on cold. Run for 5-10 min, clean the lint trap, then run for a few more. That tip was courtesy of the sales lady who I bought my fur from. The other thing I do is to vacuum the fur while making sure that it doesn't get sucked up into the vacuum cleaner… I prefer this as we will have some trimming post assembly gluing to do 

We need to cut out two rectangles of the cloth and fur that will give us an inch overhang on either side of the hair curler.  That and some hot glue and we are good to go! What worked for me was to lay the fur side down, then put the cloth part on top of the fur base. Now apply a bead of hot glue around the ends of the hair curler so that we can roll it along the cloth/fur piece. The hot glue will bleed through the cloth and glue the fur as well. I start with a bead along the top of the fur/cloth combo that will run the length of the curler. Then roll the curler onto the fur/fabric while keeping some tension on it so it adheres to the hot glue. If you don't burn a finger you are not doing it right. (little sarcasm there) When the fur/cloth combo meets itself and the hair curler is fully covered, lay a bead of hot glue down on the curler to glue down the final joint. Let it all cool. 

Now we need to trim up the excess. I tried a couple methods of covering the outside  ends of the fur/curler piece. You can cut out a small piece of fur, glue it to the end and then trim it up. Or, you can take the excess overhang, put on a dab of hot glue and squeeze it together. Either method works well. On the inside, I either used extra small pieces of fur to cover the exposed area or glued the extra overhang down. The goal is not to cover your top or front markings. 

OK, let's mount this to a camera and use it! I tried this on multiple recording setups and cameras including my Sony A7iii, DJI Pocket 2 and with additional hardware my DJI Action 2. The Action 2 used a USB interface, the Rode Micro AI Interestingly I had to wire the left and right capsules to individual jacks and go in input 1 and 2 vs making input 1 stereo. This is because the AI Micro does not supply PIP power when in stereo mode. And their data sheet tells you that. I'm actually excited about this as I have an Action 3 on order, and it accepts USB audio interfaces as well. I tried it with my DJI Osmo Action (the original) and my DJI Pocket (original) and it only worked, but only recorded in mono. Sadness. 

Note: You have to have PIP power turned on on your camera or recorder.

For audio recorders, It works really well. I used a Sony PCM A10 and my Tascam DR-05X. These make really good compact recording rigs with everything self contained. Both support 24bit 96Khz. I recorded an Orchestra with it. Here is a sample. It is 24bit using the Tascam.

The various hardware I listed will help get everything mounted. You may not need all of it.

I was really happy with how the stereo spread came across and with street video, the passing of buses and cars sounded really natural. See the testing portion of the video. I am very impressed with this capsule and can see using it in several more projects including a shotgun mic and a simple mono on camera front facing microphone. Also, the hair curler fur thing makes a great wind reduction for any small mic capsule. I'm working on a holder for the PUI 5024 to put it right in the middle of the curler. Stay tuned!