Updated: Jun 23
Using Scrap to Make Cool Things
I've always been a fan of DIY projects and making creative use of things that might be scrap to one person; I like to look for opportunity! I came across an old satellite dish, and thought, hmm... there's a few things I could do with this, and so I got to work! My first use was simply strapping it to my body and then holding my drone controller near the focal point to see if I could extend the range of my drone. (See that test here.) The result, 25% extra range boost, pretty cool! Without it I reached 833m and with the dish, 1037m. I would imagine I could yield even better results if I lived outside a gigantic Indian city! So after having a little fun flying my drone around the city of Bengaluru, I thought, how else could I use this old satellite dish? Then it was obvious, a parabolic microphone setup, like those microphones you'll often to on the sidelines of a football game. The usefulness of those are to capture distant sounds and also reduce external surrounding noise. In the way of field recording, this setup could expand my arsenal of options when trying to capture animals in the wild, for example, or even just any general use in capturing sounds in an environment where I have no control over the surrounding noise in the area and location of the recording.
Starting the Build
You can see below what I started with. An old satellite dish, with a receiver already mounted at the dish's focal point. You will notice it's not exactly centered, and I'm not exactly certain why this is, but I would imagine it has to do with the fact that the dish is not shaped as a perfect parabola. It's not a perfect circle, it is slightly oval in shape. To put this focal point to the test, I used a high powered green laser to shine at different points of the dish, and found that it always reflected back to that receiver, boom, one major calculation already covered, thanks TataSky!
The first step was to be able to mount a microphone in that same focal space. By a strike of luck, one of my shock mount microphone clips was exactly the right fit, and so I swapped that in place of the old receiver.
Make it Look Pretty!
The next step was making it look not like scrap! I spray painted the dish and slapped a stencil of my logo on it, and boom, now I can bring this out in the field and not look like a homeless guy on his way to the scrapyard! After that I also knew that I would need this thing to have some mobility out in the field and the ability to reposition it to hone in on the sound source. To help with this, I added sound handles on each edge of the dish to provide some amount of decoupling and reduce handling noise that would travel through the metal and interfere with the recording.
The Final Setup
Lastly, I build a custom microphone stand holder for it, it is a serious shoulder workout, holding this thing for a lengthy period of time. And voila, It is ready to go out in the field for initial testing!
Not knowing a whole lot in the way of recording with a parabolic microphone fixture, I set out and planned to test a variety of different microphone types, to see what ended up yielding the best quality, and directionality in a setup like this.
These are three mics in my arsenal that I thought would perform best for this job. (left to right: Audio-Technica BP4029, Sennheiser e614, Giant Squid Omni Lavalier) My assumption is that the e614 will yield the best results considering it's the only one of that has a cardioid polar pattern, but we'll see!
I'm going to share some of the details of each of these microphones, which will help get a better understanding when considering a parabolic setup and what might work best. Some companies provide very detailed specifications of their microphones, and some do not. Wether it is because they don't have the equipment for testing, or if they're hiding something varies and could be a large debate all of it's own. Regardless, I'll provide as much detail on each of the mics tested in this scenario as I can. I will include price as well, because, price doesn't always equal quality, especially in unique cases like this experiment, where there are a lot of factors at play.
Frequency Response: 40Hz - 20,000Hz
Signal to Noise Ratio: 70 dB SPL, 1 kHz at 1 Pa
Notes: I used the LR stereo narrow setting for this test. I was most worried about how this one might end up sounding, considering it is a long microphone and turned out to be impossible to mount the capsule at the exact same focal point as the others. Secondly, because it's a stereo mic, I worried that might play into the directionality of this setup, which is also why I chose the LR stereo narrow setting, to give it the strongest directionality I could.
Frequency Response: 40Hz - 20,000Hz
Equivalent Noise Level: 24 dB(A)
Notes: Sennheiser doesn't provide a signal to noise ratio, instead an equivalent noise level, which is very different and hard to compare side by side. This is the mic that I had the best expectations for since it fit right into the focal point and also has a cardioid polar pattern.
Giant Squid Omni Lavalier
Frequency Response: 20Hz - 20,000Hz
Signal to Noise Ratio: 62 dB
Notes: This is a low-end mic I picked up when I was recording my jetski, and they provide very little detail on the specifications of their mics. I found out that it is a microphone that can handle quite high levels of heat and high levels of volume before it will melt or break! I had originally planned to use it as a spot mic inside the jetski's engine compartment. I wanted to get some raw engine grind without worrying that I might melt a microphone, considering it's an airtight enclosure with high power and extreme levels of heat. It ended up a fail for this usage, as the omnidirectIonality not only picked up the engine, but also a lot of resonance inside the engine cavity, which was quite unpleasant. This mic has a fair level of inherent noise to it, but when it's placed on loud sources, that issue is mitigated, it remains a good go-to mic for loud sound sources, and things that are hot, like when I recorded flamethrowers, or under the hood of a classic muscle car. Not to say it's a bad microphone, it just has characteristics about it that make it ideal in certain situations and less ideal in others. I don't have much hope for it in this parabolic setup, but I figure it would be interesting to test it anyways!
Testing Results (Parabola or No Parabola)
First, I'll share the results of just the parabolic setup vs not having the parabolic setup, with the same microphone pointed at the same source. This will display how well the directionality changed and how useful this setup can be!
This is the BP4029 mic pointed towards some birds in a tree without the parabolic setup:
And here is the BP4029 mic again, fitted in the parabolic setup:
Immediately you should hear what a difference that makes! In the first recording (no parabola), you will hear many things besides the birds in the tree. Car horns, wind, the white noise and rumbling of AC units and machinery from a far all muddy the recording. In the second sample you can really only hear the birds in the trees and a slight but unintelligible noise floor. It would be impossible to not have some external sound when I'm in the middle of a city, plus I might be picking up some of what's behind that tree as well. In conclusion, the parabolic setup is a great success, and I was quite happy to discover how well the parabolic setup helped tune into a single sound source!
Testing Results (Microphones)
The next thing I wanted to test was a few different microphones in the setup and see which provided the best results. Note: these next samples were filtered a bit to further reduce the noise floor and since I was targeting the recording of birds which have a primary range of somewhere between 4kHz and about 14kHz. Each of the samples were filtered in the same way.
Here is the BP4029:
Next, is the e614:
And lastly the Giant Squid Omni Lavalier:
I was not surprised to find that the e614 performed the best with this test, and the Giant Squid Omni performed the worst, letting in traffic noise and such. The polar pattern in a parabolic setup plays a major role in the strength of directionality. I was hoping that maybe the BP4029, in it's almost cardioid pattern might be a contender, however, it still feel a bit short. Now there's a few reasons that might have been. One, it's polar pattern is not completely cardioid, and two, it's a long microphone, so it wasn't able to sit in the exact same focal position as the other mics, either way, not the right mic in this type of setup.
Now that I know which mic to use when I am presented with an occasion requiring a laser focus, I wanted to see how clean and pure I could get those bird sounds! After some precise filtering and noise cleanup work, I ended up with a few beautifully isolated bird calls, uninterrupted by the noise of the city!
Have a listen here:
I really love doing projects like this, and I am always happy to expand my arsenal of recording tools. I hope you all learned something and maybe this will inspire another DIY recording type project. If it does, please share it with me, as I would love to see what other ideas you all might have!
About the Author
Chris is a veteran audio professional who has won multiple awards for his work and brings an unwavering passion to his craft. He has created and programmed sound for toys, games, prototype products, records, apps, film, tv, commercials and more!
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