91–100 of 191 posts
"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."
Is there one saying “All electronic devices are smoke machines, some can compute too”?
Earlier quoted context omitted.
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…
Can an ideal gas of same volume, mass and temperature be brought to different pressures? https://courses.lumenlearning.com/suny-physics/chapter/13-3-...
An ideal gas’ pressure is a function of number of particles per unit volume, its temperature, and nothing else. If you do anything involving adding or removing heat or changing the volume or pressure, you probably also need to know the specific heat at constant volume and the specific heat at constant pressure or, frequency, their ratio. That ratio is called the adiabatic index or the heat capacity ratio, it’s written as gamma, and it’s the last parameter in the speed of sound of an ideal gas. Interestingly, it doesn’t vary all that much between different gasses.
"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.
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.
Earlier quoted context omitted.
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
A lot of people like myself consider heat a form of light but I guess a photographer would be just thinking visible light. They say that about 50% of the sun's light emissions comes in the infrared frequencies.
But I may misunderstand your comment.
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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/la…
Coriolis corrections are thrown into sniper ballistic calculations, too. Not a huge effect in most conditions, but not zero, and there have been a lot of long shots in the past two decades.
What about a soundfield microphone? Does about the same thing and the electronics can be done in the analogue domain.
Of course, you can improve on the rejection of off-axis sound by instead using a microphone with a more specialized polar patten (e.g. a shotgun mic), but then you lose the property of the pattern being steerable merely by signal processing.
Lastly, such an array of dirt cheap pressure sensitive mic capsules with some clever computation behind them strikes me as the sort of thing you could throw Moore's law at, if you could justify the quantity. Whereas, Soundfield mics don't make much sense unless you're working with very precisely machined pressure-gradient capsules.
Still, I get the feeling it'll be a while yet before this technique starts looking viable for audio production work, but it's very interesting.
Earlier quoted context omitted.
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 form…
There are at least 4 different types of microphones. Condenser which does in fact form part of a capacitor, dynamic which is effectively a linear generator (coil attached to membrane), ribbon which is a change in resistance as a small ribbon flexes and piezoelectric which is some black magic witg crystals
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.
"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.