Parabolic Dish Microphone

NOTE: THIS IS A WORK IN PROGRESS. The mic has been assembled and tested and it works! I haven't done frequency response tests but I will update this page with testing and audio once I have time to do so. 

One issue that needs to be addressed is that a single connection for the handle is inadequate because the dish wants to spin. I’m working on a solution - either a 90 degree attachment point or a two-bolt design/adapter. 

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A parabolic microphone is a microphone that uses a parabolic dish to gather and focus sound waves to a focal point where the sound can be collected and sent to a standard audio recording or listening device. While not as high in fidelity as a shotgun microphone, they are quite good at picking up audio from a single direction. This makes them useful for amplifying sounds from a great distance. They are often used in sports broadcasting and field recording.

Wildtronics, Inc. produces excellent parabolic microphones. They are vastly more affordable than those of their competitors but I wanted to try my hand at a semi-DIY version. Thankfully, they also sell their very well made polycarbonate dishes by themselves for DIYers. 

This model contains four components:

• The front and back plates are designed to hold the dish and provide a mounting location for the microphone. 
• The mic clip is designed to hold a Clippy EM272 microphone onto the support arm and route the cable back toward the center of the dish. 
• The mic mount is attached with strong magnets to the back plate and allows the assembly to be quickly broken down so the most delicate and sensitive piece (the mic) can be easily stowed in your bag and protected while hiking to or from a field location while the more or less indestructible polycarbonate dish rides on the outside. 

Weight

Mic Mount (with aluminum arm, mic clip, Clippy mic with cord and XLR connector)
97g / 3.4oz

Dish Assembly (front/back plates, gaskets, and polycarbonate dish)
687g / 1lb 8oz

Handle 
172g / 6.1oz

Total Field Weight
952g / 2lbs

Caveats

Uncovered, an omnidirectional microphone like the Clippy is not ideal for a parabolic dish and will lose some audio in the 800-1500Hz range but they are tiny, inexpensive, and have very low self-noise. One could certainly redesign the clip for a lavalier cardioid microphone. I'm open to other suggestions as well. I may try to come up with an audio baffle - like a little “hat” that goes on the end of the support arm to block sound hitting the back of the mic. We'll see.

Printing

• I printed these with PETG with a 0.4mm nozzle on a textured sheet
• 0.2mm layer height, 5 perimeters
• The front and back plates need ~50% infill for good rigidity.
• The smaller mic mount is ok with 15-20% infill.
• Print the front plate with the flat side down. Support is only needed for the screw holes.
• Print the back plate with the back side down. Support is needed for the insert hole and for the mic mount socket but not for the bevel around the edge as it is at 45 degrees.
• Print the mic mount with the insert hole facing up.
• When slicing the mic mount, insert a pause at the appropriate layer to add two of the magnets. Ensure that they are installed in the same magnetic orientation.

In addition to the printed parts, the following hardware will be needed:

• A parabolic dish with a 3 ¾" center hole like those offered by Wildtronics
• A Clippy EM272 microphone (or design your own clip and use something else)
• 4x 0.375"x0.375" cylindrical magnets
• 2x ¼"-20 heat set inserts like these from CNCKitchen
• 4x 5mm heat set inserts 
• 4x M5x16mm hex head screws
• 2x M3x8mm hex head screws
• 2x M3 hex nuts
• 1x ¼"-20-9" connecting rod, cut down to ~7"
• 2x foam or rubber gasket, ~ 1-2mm thick 
  • A standard circular gasket will not work well because of the conical section of the dish plates. You may need to source and cut this yourself. Thin neoprene, rubber, or silicone would be suitable. The goal is to dampen vibrations between the dish and microphone element. A DXF file is included below that can be used with a laser cutter or printed and used as a template for manual cutting. I used a piece of 6"x6" “gasket rubber" from my local Ace Hardware.
• 1x Camera Grip with Ball Joint
  • There are lots of these around. The linked handle is merely a suggestion. Many options are possible depending on your application. It's nice to have something with a ¼"-20 hole on the bottom of the handle so you can mount it on a tripod if necessary.

Assembly:

1. Install the four M5 inserts into the four smaller holes on the dish-side of the back plate.
2. Install one ¼"-20 insert into the hole on the rear of the back plate.
3. Install one ¼"-20 insert into the hole on the front of the mic mount.
4. Ensuring the correct magnetic orientation, press-fit the remaining two magnets into the back plate. Double check this before you press the magnets in as they are difficult (but not impossible) to remove.
5. Use contact cement or similar to glue the gaskets to the front and rear plates. The mic mount gasket will help the mic mount not to twist and should also help with vibrations. The magnets are plenty strong to keep it in place.
6. Sandwich the dish in the following order: back plate, gasket, dish, gasket, front plate.
7. Install the M5 screws through the front plate, through the sandwich, and into the M5 inserts in the back plate, ensuring that the holes in the center of the plates are aligned. 
8. The focal point of the Wildtronics dish is 4.5" from the edge of the cut hole (or the inner surface of the back plate). That's ~5.5" from the bottom of the ¼"-20 insert in the mic mount when attached to the back plate. The mic clip is approximately 1" in length. Adding that all up, you'll want to cut down the connecting rod to 6.5-7" and round off the sharp cut. If you want to be really clean, trim and round one threaded end down by about ~1" and then cut the rod to a total length of ~7" so you don't have excess threads at the base. I actually left mine at ~7.5" for a bit of focal flexibility. Add a dab of thread lock fluid and attach the rod to the mic mount. 
9. Position the mic clip so that the mic's face will be held 5.5" from the mic mount and use the M3 hardware to fasten the clip in place so the microphone is held directly over the center of the dish. You may need to experiment with this placement - getting the mic in the precise focus is crucial to good performance.
10. Stick the microphone through the hole in the mic mount, slip the cord of the mic through the slot in the clip so the mic faces the mic mount, and gently press the mic into the clip. Route the cord back through the groove in the center of the clip and add a couple of small zip ties to keep the cord from flopping against the rod.
11. The mic mount assembly can now be slipped carefully through the hole in the center of the dish mounting plates and the magnets will hold it strongly in place.
12. Attach a handle of your choosing to the ¼"-20 threaded insert in the rear of the back plate.

Now go record something interesting!