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Phased Array Microphone (2023)

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Re: Phased Array Microphone (2023)

#61

Post by killjoywashere »

Salmonfisher11 wrote: post #46
killjoywashere wrote: post #13

I wonder how well this would work with laser microphones on a pane of glass. Can you infer keystrokes with near infrared laser? That is, can you identify the heatmap of keystroke events to infer which keyboard they're using, then replay the tape to identify the strings of characters being typed? Can you localize the turning of pages with UV?

Didn't Israeli students show that you can recover audio from the vibrations of bulb filament with a fast photo diode? I'd test that with a CCD line sensor plus a wide aperture lens and reading it out with 8kHz. Then you have 128 audio pixels that can cover an entire city.

Line of sight might be an issue there. I'm thinking more high-end clandestine eavesdropping. Fun fact: curtains are a pretty good defeat for laser microphones, but if the building is really old and made of solid stone, you can point at the rock instead!

Re: Phased Array Microphone (2023)

#63

Post by adolph »

Marthinwurer wrote: post #27
frankus wrote: post #15

"As part of the calibration, the speed of sound is also a parameter which is optimized to obtain the best model of the system, which allows this whole procedure to act as a ridiculously overengineered thermometer." Reminds me of the electronics adage: "all sensors are temperature sensors, some measure other things as well."

I love these kind of inadvertent measurements. One of my favorite examples is that a sufficiently accurate IMU can get you relatively accurate longitude measurements from the Coriolis effect.

Slight correction, latitude, not longitude.

The earth’s surface closer to the poles has less distance to travel for any rotation than the surface closer to the equator. As a result the inertial navigation systems of long distance systems must be adjusted. Iirc, this is also the case for artillery firing computations.

https://www.oxts.com/blog/going-round-circles-earth-rotation...

https://www.britannica.com/science/latitude

Re: Phased Array Microphone (2023)

#64

Post by 01HNNWZ0MV43FF »

Marthinwurer wrote: post #27
frankus wrote: post #15

"As part of the calibration, the speed of sound is also a parameter which is optimized to obtain the best model of the system, which allows this whole procedure to act as a ridiculously overengineered thermometer." Reminds me of the electronics adage: "all sensors are temperature sensors, some measure other things as well."

I love these kind of inadvertent measurements. One of my favorite examples is that a sufficiently accurate IMU can get you relatively accurate longitude measurements from the Coriolis effect.

Is that the same thing where a flat-earther tried to measure something with an expensive laser gyro and kept finding that Earth was rotating?

Re: Phased Array Microphone (2023)

#65

Post by pants2 »

amluto wrote: post #59
entropicdrifter wrote: post #38

Earlier quoted context omitted.

It does act as a thermometer, if and only if the altitude remains constant. The speed of sound fluctuates with both temperature and altitude

I’m not sure how the speed of sound could depend on altitude, even in principle. The air doesn’t know where it is! Putting that aside, in an ideal gas, the speed of sound depends on the composition of the gas and the temperature and, interestingly, does not depend on pressure, and pressure is the main way that the altitude would affect the speed of sound. So measuring the speed of sound in air actually makes for a pr…

In liquids the speed of sound is related to the density, I would have thought similar for air but I see your point. Very insightful!

Re: Phased Array Microphone (2023)

#66

Post by KeplerBoy »

adammarples wrote: post #55
KeplerBoy wrote: post #47

Earlier quoted context omitted.

one might say air pressure changes constantly as we speak.

Isn't air pressure the only thing that microphones actually measure?

By definition, sure. But one always needs some effect which changes some electrical property. We can't just hook up an ADC (analog digital converter) to thin air and hope for the best.

In practice most microphones measure the displacement of microscopic membranes, which are deformed by the air pressure. The next question then becomes how to measure microscopic movements of a tiny membrane. Turns out the membrane forms part of a capacitor and the electrical characteristics of capacitors depend on their geometry.

Re: Phased Array Microphone (2023)

#67

Post by lscharen »

dllu wrote: post #3

I once did a project to do multilateration of bats (the flying mammal) using an array of 4 microphones arranged in a big Y shape on the ground. Using the time difference of arrival at the four microphones, we could find the positions of each bat that flew over the array, as well as identify the species. It was used for an environmental study to determine the impact of installing wind turbines. Fun times.

Reminds me of Intellectual Venture's Optical Fence developed to track and kill mosquitoes with short laser pulses.

As a side-effect of the precision needed to spatially locate the mosquitoes, they could detect different wing beat frequencies that allowed target discrimination by sex and species.

Re: Phased Array Microphone (2023)

#69

Post by adrianmonk »

__MatrixMan__ wrote: post #31
proee wrote: post #6

What is the most practical application for this technology? Could you use it to pinpoint sounds coming from a car like a squeak?

I wish could rent one to figure out which device in my office has a squealing capacitor. I can hear it well enough to be driven crazy by it, but not well enough to find it. I start disconnecting things to narrow it down but then convince myself that it's my ears ringing. I'm unsure if I'll age out of this problem, or if worse hearing will just recreate it at different thresholds.

You might have some luck with a spectrum analyzer app[1]. A fixed-pitch whine should show up as a line on the waterfall graph. If you move the phone around to differently locations, you might see the line getting stronger or weaker. You can also try rotating the phone to different orientations to see if it is coming from a particular direction.

I used this to locate an annoying squeal coming from some equipment at work once. And to confirm that it wasn't imaginary.

---

[1] On Android, I like these two:

Spectroid (https://play.google.com/store/apps/details?id=org.intoorbit....). If you use this, consider turning on the waterfall display in the settings.

Spectral Audio Analyzer (https://play.google.com/store/apps/details?id=radonsoft.net....). This has more color options for the waterfall display.

Re: Phased Array Microphone (2023)

#70

Post by kqr »

frankus wrote: post #15

"As part of the calibration, the speed of sound is also a parameter which is optimized to obtain the best model of the system, which allows this whole procedure to act as a ridiculously overengineered thermometer." Reminds me of the electronics adage: "all sensors are temperature sensors, some measure other things as well."

Oh yeah. I realised this the day I discovered my fancy digital SLR was a thermometer: https://entropicthoughts.com/does-my-dslr-have-dead-pixels
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