Author Topic: Microphone recommendation for finding sources of noise in electronic equipment  (Read 2715 times)

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Offline tooki

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I’m amazed that, other than the talk of putting microphones in hoses, nobody is talking about the directional characteristics of different microphones! Because what OP needs here is a highly directional microphone, which is not what most microphones are.

When it comes to microphone capsules (the actual microphone elements), they’re fundamentally omnidirectional or unidirectional, and this is determined by the mechanical construction of the microphone. (Dave did a fascinating interview with a microphone engineer some years back that goes into how this works.)

When it comes to “finished” microphones (the thing you’d give a user), the combination of capsule type and enclosure determine the ultimate directional characteristics. Those are shown in “polar patterns” that show sensitivity in a circle around the microphone.

Common polar patterns are omnidirectional (equally sensitive in all directions), cardioid (sensitive mostly to the front), and figure-8 (equally sensitive front and back, but insensitive left and right). Cardioid mikes vary in their directionality, with “supercardioid” and “hypercardioid” ones being progressively narrower (but also picking up a bit more from directly behind).

One of the most common type of highly directional microphones are frequently called “shotgun” mikes because of their long bodies.
 

Offline Coordonnée_chromatique

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“shotgun” mikes because of their long bodies.

Interesting, i'm amazed that today designs are still totally empirical and that some engeeners works profesionnaly with an "inacurate shotguin microphone" ;D
 

Offline tooki

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“shotgun” mikes because of their long bodies.

Interesting, i'm amazed that today designs are still totally empirical and that some engeeners works profesionnaly with an "inacurate shotguin microphone" ;D
Huh? I don't understand what you mean.
 

Offline Coordonnée_chromatique

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“shotgun” mikes because of their long bodies.

Interesting, i'm amazed that today designs are still totally empirical and that some engeeners works profesionnaly with an "inacurate shotguin microphone" ;D
Huh? I don't understand what you mean.

The recommended microphone with a body of a BIC ballpoint pen  :-//
 

Offline tooki

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“shotgun” mikes because of their long bodies.

Interesting, i'm amazed that today designs are still totally empirical and that some engeeners works profesionnaly with an "inacurate shotguin microphone" ;D
Huh? I don't understand what you mean.

The recommended microphone with a body of a BIC ballpoint pen  :-//
I don’t understand what you’re trying to say with any part of “ Interesting, i'm amazed that today designs are still totally empirical and that some engeeners works profesionnaly with an "inacurate shotguin microphone" ;D”.
 

Offline Georgy.Moshkin

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I’m amazed that, other than the talk of putting microphones in hoses, nobody is talking about the directional characteristics of different microphones! Because what OP needs here is a highly directional microphone, which is not what most microphones are.
wow, I've totally missed that. I guess it makes it very difficult to make an usable device. Even a sound camera has some limitations. Therefore, I thought about much simpler solution. Forget the microphone! How about using our own ears? Put some soft synthetic material on a chopstick. For example, a tiny EVA ball. Simply poke and listen if there are any audible changes. I have actually done that once, long before covid, while searching for a high pitched noise source coming from the LED driver PCB.
« Last Edit: January 01, 2025, 02:26:51 pm by Georgy.Moshkin »
better late than never
 

Online G0HZU

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A while back I bought one of these SMD microphones to make a bat detector as bats fly in my garden every summer.

https://www.mouser.co.uk/datasheet/2/218/Knowles_SPU0410LR5H_QB-2935249.pdf

The frequency range is good to 80 kHz and these things are tiny at just 2.5mm x 3.5 mm!

Part number Knowles SPU0410LR5H-QB and they are really cheap at about 60p each. Note that these are active devices so you would need to provide about 1.5V to 2.5V to power it. A watch battery (button cell) would be one option here.

 I never got around to making the bat detector, but because these things are so tiny, you will need to make a specialist PCB to mount it on as the SMD pads are tiny. I was going to mill a tiny PCB for my microphone.

You could mount it inside a short tube to make it directional. Even then the whole thing could be tiny. The alternative is a classic electret microphone element but this will be much larger.
 
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Offline Stringwinder

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A closed microphone capsule will be sensing absolute pressure no matter what
the direction to the source is. It will be omnidirectional even if you put a
tube on it.

A microphone sensitive to the pressure difference between front and back of the
diaphragm will be directional and it can't be closed on the rear side.
Bidirectional in its simplest form, sounds from the sides will be canceled.

Using a pair of pressure gradient capsules you can make many fancy variants of
directional patterns.
 

Online SteveThackery

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I'm not entirely convinced that the microphone needs to be highly directional. Provided it's small enough to be pushed between the components and get up close, I think it could still work. I recommend experimenting with some MEMS microphones, as shown in the picture.

 


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