# 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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### Is there a publication on the speed of sound assuming heat conduction is taken into account?

Is there a publication (possibly a very old one, as the topic is no longer of interest) in which the frequency dependence of the speed of sound is derived assuming heat conduction rather than purely ...
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### Why is the ground mode the only excited mode in acoustics?

If we take a disk of mass $m$ and area $A$ and place it in the middle of a pipe of length $L$ and section $A$ containg a fluid at pressure $P$ and temperature $T$ and closed from its two ends, the ...
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### Terminal speed equals to the sound speed [closed]

Qual é a altura apartir da superfície da terra em que podemos abandonar um corpo para que ele caia com uma velocidade terminal igual ou superior a velocidade do som , considerando o corpo maçico ,mas ...
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### Using superposition in coherent and non-coherent waves to find intensity

Lets say you have 2 waves that are coherent and in-phase. Both start side by side but travel towards a point A closer to wave 1. The initial intensities will be different according to I = P/A, because ...
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### Is sound really adiabatic because it is a fast process?

In many books I have consumed so far there is the statement that sound is adiabatic because heat transfer does not have nearly enough time to reach isothermal equilibrium. Doesn't this contradict ...
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### The physics behind the circle / spiral of fifths

In music theory, there is this thing called the circle of fifths. If you take a string, and you divide it in two equal parts, you get a so called octave. It is, to our ear, kind of "the same tone&...
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### What is the point of the booster/sonotrode combo in an ultrasonic cutter? Can it be replaced with a single flat sheet of metal? [closed]

I want to make an ultrasonic cutter for home use projects, something like this or there are many online videos of industrial ultrasonic cutters in e.g. the food industry. A typical design of an ...
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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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### Aliasing in Pulse Wave Doppler/Radar

There are many pictures on the Internet showing sampling of the output wave and then showing the phenomenon of aliasing, e.g.: But on the other hand, I find information that in the pulse (Pulse Wave ...
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### How to change the medium of a sound from air to bone? [closed]

I'm working on a VST which can take normal sounds and make it sound like they're traveling through bone, like bone conduction or hearing how you sound like to yourself compared to how you sound to ...
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### Can human ear hear 4 Hz frequency, if I tap my hand 4 times per second on table?

Frequency means the number of repetitions per second. Humans can hear between 20 Hz and 20 kHz, but I have a very basic question: if I tap my hand four times on a table per second, it means I am ...
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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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### Working Backwards from Pressure Field to Transducer

I am considering the problem of a pressure field generated by acoustic waves. If I know the specific pressure field which I wish to generate, is it possible to work back to a transducer (or array of ...
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### Change in Frequency while Tearing Paper

Let us assume you have a 30cm strip of paper, and you tear it lengthwise. Let us abbreviate the frequency produced when you reach the end of the paper as $f_2$ and the frequency of sound heard when ...
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### Can sound waves be modulated?

Can you modulate sound waves? Like can you have a sound wave of a relatively low frequency and modulate it with a sound wave of a much higher frequency which people cannot hear and send it through the ...
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### Cancelling outside sound without noise canceling headphones [closed]

If sound can not be cancelled because the ear is elastic could the sound be cancelled if transmitted via bone conduction
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### Types of Mechanical Waves

When knocking on a door, does that create a transverse wave or a longitudinal wave? I know it's one of these mechanical waves, but which one?
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### Is sound essentially motion?

From my understanding, the only way for humans to create sound is by moving our bodies, vocal cords, or by moving other objects. So depending on how fast we or other objects can move, different ...
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### Calculating in-duct sound intensities from sound pressure measurements with mean mass flow

In the time domain and in free field condition the sound intensity can be calculated as $\vec I(t)=p(t) \cdot \vec v(t)$ with $p(t)$ being the sound pressure and $\vec v(t)$ being the sound velocity. ...
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### In order for Sound to exist, are Spacetime, Matter & Motion required first, in that exact order?

From what I’ve read so far online, briefly reading Newton, Einstein, and Minkowski’s theories this is the order I’ve come to. I.e, for matter to exist first there has to be space and time, for motion ...
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### At what speed does information move through the atoms of a rigid object?

How fast does information travel on particles? I thought if you move a iron bar from one end it would take the speed of sound to move its other end. For example, theoretically if you hold an iron bar ...
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### How is symmetry boundary condition related to reflection of a plane wave from a rigid flat surface?

My question is in in the context of "method of images" when applied to an incoming incident acoustic pr plane wave. For a flat rigid surface in $XY$ system, the surface (positioned at $Y=0$) ...
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### If you are on the moon, would you be able to hear your hands clapping if you're not wearing your spacesuits?

As I understand it, sound needs a medium to travel and more often than not, the medium is the atmosphere, however sound can also travel through solid objects. And even we can hear our own voice ...
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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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### Why can I tell when to stop filling a glass based on the pitch of the water?

If you fill a glass of water, the sound pitch of the water increases as the glass gets more and more full. The other night I was filling a glass in the dark and I noticed something - I could ...
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### Air Columns non-resonant frequencies

I understand that both open and closed-end air columns have many resonant frequencies, called harmonics and a fundamental frequency. At these frequencies, we expect to observe standing waves of ...
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### Difference between structural acoustics and flow induced acoustics

I'm researching about sound induced inside water pipe and came up with some questions. For numerical acoustic calculation, I found two ways. Using acoustic analogy such as Lighthill equation or ...
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### Acoustic wave incident to pipe wall

I would like to consider the sound incident to a water filled pipe wall. I think the pipe wall is typically considered as a rigid wall boundary, it means all the incident wave is reflected. Is this ...
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### How can acoustic velocity of plane wave be derived using acoustic pressure?

I am going though the section on plane travelling waves from the book by G.D.Pierce,"Acoustics: An Introduction to Physical Principles and Applications". I am unfortunately stuck at a place ...
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### Calculation of Ultrasonic Attenuation Coefficient

Hello I have a conceptual question regarding calculating the ultrasonic attenuation coefficient for a transmitted wave within a solid material. I have seen Beer's Law used to calculate the attenuation ...
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### Question about the norm of the four-velocity being equal to $c$

On the way to the Einstein equation we derived the four-velocity: $$u^\mu=(c,v^k)$$ with $v^k$ being the 3-velocity, which can can be very low ($|v|<<c$). However, the square of the four ...
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### Is the strongest acoustic signal always the closest?

I have a single beam echosounder that I use to measure the distance to an object underwater. It emits an acoustic pulse and listens to the reflections. Using the time of flight and the strongest ...
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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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### Why do strings in musical instruments have helical shape?

We learn that waves travels in strings under tension, have fundamental frequencies, but I have no luck understanding why don't musical instruments have simple strings with uniform thickness which we ...
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### Optical path length for sound

The definition of optical path length is the distance that light could have travelled in the same time, in vacuum. So, can we define something analogous for sound waves, like an "acoustical path ...
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### Derivation of intensity of a sound wave (missing calculation in the book)

The question is about a calculation in the first section of this page: https://openstax.org/books/university-physics-volume-1/pages/17-3-sound-intensity Essentially, it states: "To find the time-...
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### Derivative of displacement in deriving expression for intensity of sound waves

I am currently working on deriving the expression for intensity of a sound wave: https://openstax.org/books/university-physics-volume-1/pages/17-3-sound-intensity The previously mentioned book states: ...
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### Does rhythm create pitch?

As in, matter (a physical object) that is vibrating = a pitch And secondly If we calculate bpm with a “tick” which is just indefinite pitched percussion, how does an indefinite pitched beat compare to ...
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### Sound when hitting a metal pipe: dependence on radius?

There's a fun physics exhibit at the Centrum Nauki Kopernik in Warsaw with various hollow metal pipes of different lengths and radii that you can whack with a small mallet. One section has three pipes ...
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### How do computers store sound waves just by sampling the amplitude of a wave and not the frequency?

All of this just doesn’t make sense though. I mean, doesn’t the amplitude represent the loudness and the frequency the pitch? Aren’t they completely independent from each other? Is the book just ...
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### Can superposition of ultrasound and hearable sound be heard differently in comparison to the same hearable sound without superpositioned ultrasound?

On recent audio show, I have noted down 5 rooms where sound was the best to my ears, so I can make second round to hear them again. After few days, when analysing speakers used in these 5 rooms, all ...
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### 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 ...
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### Refraction of sound atomic level

how the refraction of sound and the change in the angle of propagation can be explained at the atomic level, why the direction of propagation of molecules changes in different media?
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### The solubility of gases in liquids. Laws and equation [closed]

I am studying the solubility of gases in liquids (flowing then into the study of oscillations of gas bubbles out of the liquid phase). The task at the moment is to familiarize myself with the laws of ...
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### Is it possible to take the time derivative of sound speed of an ideal fluid when the background $w=0$?

Context: To determine the evolution for a particular unified dark matter model we use the following equation: \delta''+3(s\delta)'+(\delta'+3s\delta)\left(2+\frac{H'}{H}\right)-\...
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### Can molecular structure be explored using sound waves? (Project Hail Mary)

I have studied science till school, but not in grad... so I might very much be wrong ... isn't the wavelength of sound waves larger than the dimensions of atoms? Won't sound waves skip over atoms?
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### How can be Sound energy get converted/conserved into the Universe's energy? How does it work? [duplicate]

Is energy constant in this universe? Or the energy is conserved? Say an example, Whenever I take my foods, it converts into Mechanical Energy. And when I talk, it converts into Sound energy. So If, ...
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### Analytical Solution of Sound Wave Propagation in Moving Medium (1D Problem)

I am trying to use frequency-wavenumber analysis to estimate sound wave propagation in a moving medium (fluid). I need to test the technique on analytical data. I wonder if there is an analytical ...
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### What happens when a cavitation bubble collapses

I know that when a cavitation bubble collapses, heat is given off and a shockwave is formed. What else happens? Is there increased water pressure in that region? Can the intensity of this implosion be ...
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### Beer's Law ultrasound attenuation, account for spherical spreading?

I've seen Beer's Law for narrow beam written as: $$I = I_0 \cdot e^{-\alpha x}$$ ${\alpha }$ - attenuation coefficient (depends on absorption and scattering), $I_0$ - initial intensity, $I$ - ...