Questions tagged [acoustics]
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. Applications of acoustics are for instance the audio and noise control industries.
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Why do I hear static when I plug in my earphones incorrectly?
I use simple earphones which are wired with my laptop. Most of the times I unconsciously plug them in without looking and at times instead of going in the port they touch the laptop body near the port ...
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Are sound waves in fluids also Goldstone modes?
One usually says that sound waves in a crystal, ie. phonons, are Goldstone modes of the broken translation symmetries. However, fluids have sound waves and also translation invariance. In fact, it's ...
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Are acoustic phonons always the lowest energy vibrational modes in solids?
In solids with unit cells containing more than one atom, the normal modes show acoustic and optical branches. The number of optical branches is proportional to the number of atoms in the unit cell, ...
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Two sonic booms colliding
If I theoretically created an experiment where I could create two sonic booms in directions such that the sonic "nose" is facing each other; what would happen?
more specifically:
Lets suppose I have ...
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Does sound need an odd number of spatial dimensions?
In the book "when Einstein walked with Gödel" the author talks about Edwin A. Abotts "Flatland" stating that one problem which was unattended by Abott is the problem of acoustics ...
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How loud is the Perseus cluster?
The gas near the center of the Perseus cluster exhibits quasiperiodic pressure oscillations that can be interpreted as sound. I found a paper that says that these pressure waves have a wavelength of ...
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Sound conduction in a stethoscope
i am trying to build a stethoscope and since i have no idea about physics and acoustics i wanted to ask some questions, hoping Somebody can help me.
I mainly have some questions regarding the tubing ...
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Why are higher frequencies amplified less by filling a bottle with warmer water instead of colder water?
Out of curiosity I was trying to figure out what makes the sound of hot water versus cold water filling a bottle different, but I'm unable to find any explanation as to why such differences occur.
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Using convolution to simulate acoustic dispersion in shallow water
Background
I'm a marine biologist who's trying to wrap my head around shallow water propagation. I'm interested in how acoustic dispersion (as described by Pekeris' waveguide) alters how sounds ...
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Why do scattered waves vanish when the wavenumber of the incident wave is an eigenvalue of the interior Dirichlet problem. Where has the energy gone?
I normally work with numerical computations for wave scattering, but I am now trying to get a better understanding of the physical processes underlying the theory, in particular, what happens to the ...
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Could sonoluminescence be the result of the Casimir Effect?
My question concerns Sonoluminescence. I was amazed to learn that collapsing cavitations in liquids generate temperatures greater than 20,000 Kelvin. Is it possible that the vast amount of energy ...
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Sonoluminescence spectrum
During cavitation created by sound in a liquid the collapse of the bubbles can lead to very high temperatures and pressures resulting in the emission of light - sonoluminescence.
Can the spectrum of ...
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How to get the pressure amplitude at any spatial point?
Working on the pressure equation from the linearized euler equations, I stumble across a very simple problem :
How, from the pressure solution of the specific equation (see http://www.acs.psu.edu/...
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How can we describe the attenuation of sound in an expanding gas cloud in a vacuum?
For example, suppose a spaceship explodes. The sound of the explosion will travel in the expanding cloud of escaping gas. I gather that it should rapidly weaken and the pitch should drop, but I'd like ...
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Observed frequencies of a drum versus mathematically predicted frequencies
I built a small circular drum in order to compare the actual resonant frequencies versus the resonant frequencies predicted by modeling it as a circular membrane obeying the wave equation with fixed ...
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Room treatment: how much energy can a Helmholtz resonator absorb?
A common suggestion to dampen low frequencies in a room (and to shorten the reverberation time) is to use a Helmholtz resonator. This is typically just an airtight, rigid box with one or more vents ...
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Why does bringing a helium filled latex balloon close to my ear make it feel pressurized?
Title pretty much says it all.
Got my son some balloons for his 1st birthday. He was playing with them while I was holding him and everytime he brought one closed to my ear it made my ear feel ...
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Why does a violin sound louder when I bow faster?
When you bow a violin string, the string vibrates at a specific frequency. It sounds louder when you bow faster - that is when the string stick and slip against the bow with larger displacement (or ...
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Geometrical acoustics derivation
In acoustics for non-uniform media (speed of sound is $c(\mathbf{r}, t)$, dependent on space and time), I want to solve
$\frac{\partial^2\phi}{\partial t^2}-\nabla^2(c^2\phi)=0$, where $\phi$ is the ...
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Why is the speed of sound wave in a gas always lesser than the r.m.s. speed at the same temperature?
My book says that the speed of sound wave in a gas is always lesser than the r.m.s. speed of the gas at the same temperature. I understand that speed of sound is given by:
$$v_s=\sqrt{\frac{\gamma RT}{...
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Image method for room impulse response simulation
I am following this paper on simulating a room impulse response (RIR). The wave of a single frequency $\omega$ point sound source in location $X$ as it is viewed by a microphone located at $X'$ is:
$$...
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Relationship between resonance frequency of a cup and amount of water filled
For a science project I chose to investigate the relationship between the resonance frequency of cups and the amount of water filled in it. I filled the cup with 10 grams of water each time, and used ...
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What are all the possible ways to achieve acoustic resonance in a cavity?
If one were to observe acoustic resonance in a cavity (semi-closed volume of space) what is the complete list of potential hypotheses as to the cause?
In my limited experience I can list the ...
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Fluctuation-dissipation theorem for the acoustic equation
Recently I discovered a paper by R. Snieder on the extraction of the acoustic Green function from cross-correlations of the acoustic noise. What differs this paper from other papers on the subject, is ...
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Quarter wave matching layer of a piezoelectric transducer
I am trying to understand the quarter wave matching between two layers of impedance $Z_1$ and $Z_2$, where $Z_1 > Z_2$. I can understand the electrical transmission line analogy of matching layer ...
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Using train horn echo to measure distance?
This is not homework... it's way too hard! It's actually just a really intriguing problem I've wondered about for years while listening to trains echo through the mountains. Here's the simplest ...
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Intensity of an ultrasound beam?
I am working through question 9.1 (link to Google Books) of 'Fundamental Physics for Probing and Imaging' by Wade Allison. The question involves finding the varies quantities (such as pressure ...
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Physical Meaning of Over- / Underdetermined Acoustic Eigenvalue Problem
I am performing an eigenmode study on a system of acoustic ducts. The system consists of two large cylindrical volumes connected by several smaller cylindrical volumes (modeling a combustion chamber ...
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Proof that fixed points of a null field are zero
Suppose we have a scalar field $V$ (which can be acoustic pressure, or a scalar electric potential) that is a solution of the wave equation
$$\Box V(x,y,z,t) = 0$$
I am wondering if a fixed (non-...
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Sound waves and chromism?
I am definitely not a physicist, but I have a question related to Physics so I thought I'd give it a try. Please excuse my ignorance. :)
I am somewhat familiar with the changes in color caused by ...
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How does a sonic black hole (or dumb hole) work?
I came across this term and apparently they used sonic black holes to detect something analogous to Hawking Radiation, but I have failed to find sources which explain how exactly they work and how ...
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Ray tracing a three-way intersection
I've been studying ray tracing in media with linear velocity-depth functions. One of the key concepts I've come across is the ray parameter, and in particular the idea that the ray parameter is ...
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Difficulty implementing equation describing angular response of fibre-optic hydrophone
I am attempting to implement an equation in a paper which provides an approximation of the angular response of a simple fibre optic hydrophone. The equation in question (number 19) is repeated here ...
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Reference for the reflexion of sound in connection with boundary conditions of the wave equation
In 3D, the homogenous wave equation
$$ -\Delta_x u(x,t) + \frac{1}{c^2} \frac{\partial^2 u}{\partial t^2} (x,t) \ = \ 0 \ \ \mathrm{in} \ \Omega \times (0, \infty) $$
can approximately describe ...
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Number of wave modes in a cavity
I'm trying to calculate the number of acoustic modes that can exist in a room in a certain range of frequencies. I thought of using the Rayleigh-Jeans formula for the electromagnetic standing wave ...
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What is the longest distance over which echolocation is effective?
Some animals, most notably bats, use echolocation in order to navigate and detect the location and size of objects and prey. This usually takes place over short distances.
What are the theoretical ...
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Is it possible to estimate the number of people in a room from a limited number of simultaneously recorded audio samples?
Note: I struggled to decide the appropriate site for this question, between https://physics.stackexchange.com/, https://video.stackexchange.com/, https://math.stackexchange.com/, and even https://...
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Frequence vs speed of a moving object
Imagine swinging wood stick using hand (say it's a 1-meter long cylinder with 2 centimeter diameter, just for the sake of argument). When doing it fast (angular velocity = $\omega_1$), it will create ...
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How do lower frequencies change differently than higher ones as they travel?
I read the following on the internet:
"This means that as sound travels, its relative frequency content alters making the low frequencies more prominent at greater distances, creating low ...
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Unable to re-derive Inverse Transfer Matrix
I don't get the same result as the book when computing the inverse of this matrix.
For context, I'm rederiving some equations from a book on acoustic waves in periodic structures, specifically a ...
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Why don't we commonly use bra-ket notation in acoustics and vibration?
I have a background in acoustics and do more and more of quantum mechanics.
I wonder why don't we use more often the bra-ket notation in acoustics and vibrations like in quantum mechanics?
In modal ...
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What are the Fresnel formulas for acoustics?
While it's not too difficult to derive Snell's Law for acoustics e.g. from Huygen's principle like for light, I find surprisingly little resources on an equivalent to Fresnel formulas linking the ...
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What happens with natural frequency on a rope which length is changing?
I was watching violin concerto, and I thought of two scenarios of sliding on the string and taking finger off the string as shown in the image:
Define $v = \sqrt{\frac{T}{\mu}} = f\lambda$, $T, \mu, ...
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Calculation of sound speed profile for positive speed gradient
I have started exploring geometrical acoustics/optics in the oceans. I came across a problem that I have been working on for two days. I have mostly solved it, but I am missing just the final step and ...
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Do lower frequency sound waves penetrate through materials better than high frequency waves
I was doing a physics experiment today where we played different frequencies at the same volume and a sound recorder at the other end with a sheet of cardboard in the middle. We found that the higher ...
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The cause of higher harmonics amplitude drop in an air column?
In the case of the real life string, I believe I understand the cause of the amplitude drop as we go into higher harmonics: the bendability of the string is not infinite and as we get lower ...
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How high altitude/low pressure could you could hear a gong right next to you?
"There is no sound in space". But how thin can air be and musical instruments still be heard?
The absolute pressure limit of sound (of a given wavelength) occurs when the wavelength is less ...
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Longitudinal waves - Speed of sound vs Salinity
I have read that speed of sound in water increases with salinity "Sound travels faster in the ocean because there are more molecules — specifically salt molecules — for waves to interact with, as ...
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Exciting standing waves in piston/valve ended pipe
Suppose a pipe is connecting a high pressure with a low pressure region. Within this pipe there is a piston/valve that can be opened or closed and a large pressure drop.
As the valve is opened, air is ...