Can I acousticly shield a mic from one side?

Question

I recently got into ambient recording and bought an inexpensive Zoom H1N. I did some test recordings at max gain to see what it would pick up. I aimed at a small fountain in my garden, from some distance, to have a natural sound. The recording however was extremely noisy. I live on the outskirts of a big city, I did expect some noise, but not that much.

So I tested it inside, in a quiet room, and realized that some noise came from the device itself.

I then spent some more money on a pair of Clippys (EM272) and repeated the indoor and outdoor test.

Indoors the more sensitive Clippys require only gain 6 (instead of 10) for the same results. But outdoors the noise seems to come from the city and not the mic. As the Clippys are omnidirectional, the result is actually worse than the cardioid pattern internal mics from the H1N.

As I will not always have a spot to aim at a shotgun mic doesn't make much sense and would be more expensive.

I read about audio isolation boxes and researched the topic. Sound proofing vs. sound absorption. So I was wondering if I could build a contraption like such a box to shield the mic from one direction as the noise mainly comes from the direction of the city. I would like to block between 300 Hz and 2 kHz coming from this one direction. I have given up on blocking under 300 Hz as it seems to be too difficult according to several articles about it. I don't need full blocking but a good reduction would be really nice.

I was thinking about a box made out of 19 mm (?!) MDF with one side open. Maybe some acoustic foam inside and the mics at the very end. But I have no clue what size, shape or length i need. I do want to capture about 120° down to 90° and no less. So the box can't be too much of a tunnel but if it's too short, I fear it will not block much from the sides. It should be portable, but as the mics are tiny, the size of the box can be as well.

Questions would be:

• can this be achieved with acceptable results ? (without breaking the bank)
• Is my idea with the box going in the right direction or would a simple podcast acoustic shield suffice ?

I'll add a snippet of what the current noise looks like in audacity.

Edit:

I uploaded a pure "what I consider unwanted noise" file to my gdrive. (you can comment there to not spam the comments here)

https://drive.google.com/file/d/1uj6CqVxOjhIYc6FCzLOCfCIC2ahxAY-i/view?usp=sharing

Answer 1

Sounds to me you don‘t know about wave effects, including the mics polar sensitivity.

You are not in optics, where natural objects, like people (2m) are much larger than the wavelength (green: 500nm or 0.0005 mm).

In sound, 300 Hz correspond to 1 m, or 0.1 m for 3 kHz. So objects smaller than that will cause waves of that frequencies to diffract, i.e. propagate around objects. Interference sum up or annihilate amplitudes depending on phase differences, i.e. vary much in spatial directions.

So your box or shield idea won‘t work, unfortunately. Though, it will change sound impression, especially indoors. Search for comb effect.

What do professionals do?

They shield against wind with some fluffy stuff over the mic. They use mics with high directivity (cheap mics are sensitive to almost any direction, very expensive ones in a „narrow“ coil forward).