Questions tagged [noise]
306 questions
58
votes
3 answers
Why doesn't oil produce sound when poured?
I've noticed that unlike other liquids, when pouring olive oil for example, I don't hear any sound at all from it.
Usually you can hear an audible sound as a cup gets filled with water, as the sound increases in pitch.
What makes the oil behave this…
Moshe
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50
votes
3 answers
What would a blackbody sound like?
If a blackbody has a temperature such that its peak frequency was well within our audible range, for example $1\ \mathrm{kHz}$, what would that sound like if we used Planck's law to plot its spectral curve in the frequency domain and performed a…
ayane_m
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41
votes
3 answers
What is the reason for this pattern of noise in electric kettles?
It always seemed to me that the noise from electric kettles follows a pattern: It starts low, then increases, and decreases again before the water starts to boil.
To verify this, I performed a little experiment: I recorded the kettle using my…
Lior
- 3,490
25
votes
2 answers
Maximum delay for effective active noise cancelling?
Active noise cancelling reduces unwanted sound by sending the inverted phase of the original phase:
(Source: Wikipedia)
Theoretically, this seems logical to me. However, in real life, the anti-noise must be created by some hardware or software…
Uooo
- 261
18
votes
3 answers
What information is contained in the quantum spectral density?
Consider a harmonic oscillator system with Hamiltonian
$$\hat{H} = \frac{1}{2} A \hat{u}^2 + \frac{1}{2} B \hat{v}^2 \qquad
[\hat{u}, \hat{v}]=i \gamma $$
where $A$, $B$, and $\gamma$ are all real.
This system has resonance frequency $\omega_0 =…
DanielSank
- 25,766
17
votes
1 answer
Why is Johnson noise a Gaussian process?
Noise processes in engineering and physics are frequently assumed to be Gaussian processes.
This allows use of convenient analytical techniques.
The question then arises as to why natural processes are Gaussian.
In particular I'd like to understand…
DanielSank
- 25,766
16
votes
1 answer
What part of the fan blade actually does the noise generation?
I'm trying to identify the sources of noise in spinning fan blades and what causes them.
Is the noise only generated by the lead edge of the blade 'cutting through' air? and different parts of it (closer to hub vs away from it) have different…
MandoMando
- 303
16
votes
1 answer
Relation between Langevin and Fokker-Planck for exponentially correlated noise
What is the corresponding Fokker-Planck equation for,
$\frac{df(t)}{dt}=-kf(t)+\zeta(t)$
where, $\zeta(t)$ is random noise? In particular, how will the Fokker-Planck equation look if $\zeta(t)$ is exponentially correlated (or coloured, see this…
nitin
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14
votes
3 answers
Does this thought experiment violate the second law of thermodynamics?
Consider an adiabatic box with an adiabatic board in the middle, which separates the box into two parts. There is a small hole in the board next to a coil, and the hole has a door which opens when the current in the coil reaches a certain…
alst
- 257
13
votes
1 answer
How does LIGO remove the effects of environmental noise?
Since LIGO is dealing with readings at nanometers, events such as vehicles driving nearby, and constant (but extremely minor) tremors of the earth can cause movement with the mirrors at nanometers.
Such tiny movements are extremely difficult to…
Jack Weatherilt
- 133
12
votes
3 answers
Avoiding radar detection using active noise control instead of a stealth fuselage
was reading about different stealth technologies used by modern aircrafts to avoid radar detection.
Wouldn't it be easier to have a receiver on the airplane listening on the radar frequencies and then re-transmit that same signal but phase shifted…
Henry Skoglund
- 131
12
votes
3 answers
How can IR cameras see things colder than the camera?
I’ve read that only cold-blooded animals develop IR vision to spot warm prey because a mammal would blind himself with his own heat and not be able to see anything.
But I’ve seen a FLIR camera, operating at room temperature, able to image warm and…
JDługosz
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11
votes
9 answers
Feynman claimed "The ear is not very sensitive to the relative phases of the harmonics." Is that true?
In The Feynman Lectures on Physics, Dr. Richard Feynman claimed that the ear (I assume he meant the human ear) is not sensitive to the relative phases of harmonics.
However, I was asked to test electronic filters with a Textronix Vista tester using…
Dan Bullard
- 149
11
votes
2 answers
What causes this strange noise in a pair of walkie-talkies?
Let us suppose that Bob and Alice both have walkie-talkies. They are both 3m apart from one another. Alice pushes her walkie-talkie to speak but instead of speaking, she starts walking toward Bob. Both Alice's and Bob's walkie talkies are facing…
JW Feynman.
- 143
10
votes
2 answers
Is it possible to noise cancel a sonic boom?
I having trouble understanding how a sonic boom works exactly. I know that it is done with sound waves and that ALL sound waves, at least on Earth, travel through a medium which effects it's speed. So when something travels at speeds higher than…
user3097852
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