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Mics mono/stereo (1 Viewer)

besaide

Active member
Feel free to ask for details if necessary.

Cheers)

I have readed this post with a lot of useful information: DIY STEREO PARABOLA

When I bought the squirrel, I was going to copy the Figure 15 but I was afraid of the handling noise, this is why I did the housing, but with the housing I lost something very important that I didn't realize at the moment, this is written under figure 3:

"a physical effect used by a special sort of microphone, the boundary microphones or pressure zone microphones, comes into play: If sound waves hit a non-absorptive boundary, the signal of the direct and reflected signal add up and double sound pressure, thereby increasing the peak gain by 6dB"

This physical effect is what I think is being used in this other system with an acrylic pyramid:

DIY microphone system for tuning into avian nocturnal flight calls

I have to do some test to understand better all this information and work out how to use it.

The "squirrel" is for static recording whereas the "umbrella" is for hiking. I both cases the main goal is bird ID = Birdnet in real time + recorder (audacity at home)
 

Vollmeise

Well-known member
besaide,

in the case of a boundary microphone, a microphone capsule has to be inserted flush into a plate with a flat, smooth surface (the microphone capsule must not protrude from the surface).

To realise this you could, for example, take a discarded CD, in whose central opening you fit an AOM5024L so deep that ultimately a single level is created.

Two pieces of these CDs with integrated microphone capsules are then connected "back to back", so that the two microphone openings point opposite to the outside (left/right channel).

This boundary microphone arrangement is then mounted in the parabolic mirror exactly at the focal point of the parabola.

As Your squirrel seems to be more bowl -shaped, there might be no amplifying effect as a parabola could deliver. Same could be with the umbrella, depending on it's shape. Another problem could be the umbrella's fabric's surface, which maybe will not deliver a total reflection (some of the sound might pass through it).

So I really recommend to make a perfect shaped parabola by yourself or buy one as a spare part.

Cheers)
 

besaide

Active member
Vollmeise,

Thanks for all the information :)

I have dismantled the housing and done a quick prototype with a 100mm diameter dish (2mm acrilic). As soon as I get the new mics I am going to do it much better.

The "umbrella" is better option for me than the real parabolic dish because I hike a lot = Osprey exos 46 + 8x32 and Nikon P1000 (resting on the shoulder straps). The "umbrella" goes with a carabiner also on the shoulder strap, or can go like trekking poles goes in the osprey system (under armpit). The main function is bird ID (birdnet) in real time for those days where I go to new places. Everything has to be at hand.

For fun, I will try the real parabolic too :)
 

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Birdspotter

Well-known member
How many centimeters should I place the mic from the base on a dish 40 cm diameter and 17 cm height? It's the typical squirrel baffle. Any recommendation to make good use of it?
I attach a pic of how I plan to do it.
I am also presently looking at making a home made parabola by using a squirrel baffle. Although i have thought about using a wooden dowel as in your picture to hold the mic in position, I think i might go down the route of using the wire frame of an old light shade.
The circular section that holds the shade onto the light bulb casing looks to be a perfect fit over the inner side of the baffle fittings, simply unscrew the baffle fitting and fit over the frame as you would a light bulb.
By using a wire cutter it's just a matter of snipping the circular bulb section off the light shade frame, remembering to leave one length of straight wire that can be bent into place were you would attach your mic onto at the top.
Although this idea of mine sounds like a good idea I have yet to try it out as I haven't acquired an old light shade at this moment!

Also I have yet to work out a good handle that means I can keep the baffle fitting (thus the mic holder) in place too.
 

Birdspotter

Well-known member
Just went out and purchased these for a few pounds. Biggest price was the lampshade at £8 as I never had an old one to hand.
Everything was screwable, with the exception of push fit fixings to pipe & the handle cover that needs glueing on.
Mic fitting needs some work still but just a few pics to see what I set up at a cheap price.
I know my recordings will not be as good as a real parabola but as a start up to this form of recording I think it is a good option. 6A657947-E5F5-4317-837A-E64CA383FC65.jpeg
 

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Birdspotter

Well-known member
BE636969-C851-4877-871E-AC8E5C22F336.jpeg
As I say just a few adjustments to the mic holder still, as well a try and gauge the sound focal point.
The mic cable runs down through the handle to the recorder. Again the cable will need some kind of fixing (masking tape) to the bowl to stop any noise through movement.
 

besaide

Active member
besaide,

in the case of a boundary microphone, a microphone capsule has to be inserted flush into a plate with a flat, smooth surface (the microphone capsule must not protrude from the surface).

Another problem could be the umbrella's fabric's surface, which maybe will not deliver a total reflection (some of the sound might pass through it).

Today I have done some outdoor tests :) comparing the umbrella "new prototype" and a "normal" mic.

The backpack has an AOM 5024L (with battery box) connected to the olympus LSP1 recording all the time while I am hiking. It has also a TRRS output for birdnet, the smarthphone goes in the green bag.




Detail of the housing without the mesh bag (after this test... I am going to modify this housing and will add an acrilic dish)



For the test I have used a firecrest audio from Merlin ID.



With GAIN 8 and 5 meters away the umbrella records 14dB more than the backpack mic (with the mesh on)

With GAIN 10:

3 meters away = 25 dB difference (more or less)
5 meters away = 21 dB difference
8 meters away = 22 dB difference

Note: It was very windy!! At the end of the test the umbrella has gone flying... and the battery compartment has broken :-( I have fixed it at home :)
Never leave a parabolic dish alone in windy conditions :)

 

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Vollmeise

Well-known member
With GAIN 8 and 5 meters away the umbrella records 14dB more than the backpack mic (with the mesh on)

With GAIN 10:

3 meters away = 25 dB difference (more or less)
5 meters away = 21 dB difference
8 meters away = 22 dB difference
Besaide, thx for sharing Your tests with us. I can see that you put a fair amount of effort into getting the best results.

I think, however, that I have not yet fully understood your comparison setup.

- the source of the singing firecrest was placed fix?

- Your backpack recorder and mic was placed fix also? If Yes, at which distance to the firecrest speaker? Which Gain settings (in comparison to Your gain dependent results)?

So did You compare

1.
gain [email protected] (backpack mic w/o umbrella)
versus
gain [email protected] (mic w/ umbrella)
Result: 14 dB difference

2.
gain [email protected] (backpack mic w/o umbrella)

versus

2.1
gain [email protected] (mic w/ umbrella)
Result: 25 dB difference

2.2
gain [email protected] (mic w/ umbrella)
Result: 21 dB difference

2.3
gain [email protected] (mic w/ umbrella)
Result: 22 dB difference

So in summary the understanding is, that increasing gain by 1 step will lead to an amplification of 3 dB. This is a recorder specific result, btw. Another result of Your setup is, the nearer You go to the source, the louder the signal You'll get.

Those results do follow basic physics as they should do: If you double the distance to the sound source, the volume level is reduced to a quarter (around 6 dB). Results 2.3 should be lower than 2.2, maybe there is a source of error?

Cheers, Vollmeise
 

besaide

Active member
- the source of the singing firecrest was placed fix?
Yes, I used the smartphone (Merlin bird ID) for the firecrest audio. Always the same song, level at maximun in my phone. It was on my hand. Umbrella and backpack on the boulder.
- Your backpack recorder and mic was placed fix also? If Yes, at which distance to the firecrest speaker? Which Gain settings (in comparison to Your gain dependent results)?
I have 2 olympus LS P1. One is for the backpack and the other one for the umbrella. Both were recording in manual mode. Low cut filter ON. Both recorder were connected to its battery box.

I took this photo to show how the umbrella and the backpack where placed. Both mics are more or less at the same distance from me. The wind was strong and the umbrella was moving a little bit.
I recorded around 40 seconds with gain 10, I was standing 3 meters away from the boulder with the smartphone on my hand . Then another 40 seconds 5 meters away and another 40 seconds 8 meters away (more or less).

I did another test with gain 8 but only 5 meters away from the boulder.

So in summary the understanding is, that increasing gain by 1 step will lead to an amplification of 3 dB. This is a recorder specific result, btw. Another result of Your setup is, the nearer You go to the source, the louder the signal You'll get.

Those results do follow basic physics as they should do: If you double the distance to the sound source, the volume level is reduced to a quarter (around 6 dB). Results 2.3 should be lower than 2.2, maybe there is a source of error?

Cheers, Vollmeise
I have checked again the audio and removed the wind sound to analyse only the firecrest signal. This was the source of error :)

With GAIN 8 (LSP1):

5 meters away from the boulder = 13,9 dB difference between umbrella and backpack. (Better umbrella)

With GAIN 10:

3 meters away = 28,1 dB difference
5 meters away = 25,3 dB difference
8 meters away = 21,9 dB difference

It was not the best day for a test like this, but I wanted to try because I was using the umbrella with birdnet and it was better than my previous umbrella prototype with the housing. I was surprised! and very happy :)
 
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