# Tagged Questions

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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### How can pressure and velocity fluctuations in acoustic plane waves be in phase and still hold to the B.C. that velocity must be zero at a solid wall?

In linear plane-wave acoustics (no mean flow, small perturbations, etc.), it is often derived that the phase of a traveling pressure fluctuation wave and a fluctuation velocity wave are the same. For ...
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### Audio attenuation over distance

In a completely open space, we position one speaker. The speaker emits a sound at X dB. How can I calculate the sound's volume at a specific distance? Also, how can I calculate the attenuation of a ...
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### How can a harmonica make some different sounds?

My first post: I have found an interesting harmonica here. So, I tried to know more about harmonica. And, I have read this article , in which the author doesn't mention the physical calculation, ...
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### Why does sound not travel between media?

So imagine you're at the beach; you go into the water and the moment you enter the water you stop hearing anything from the outside world. The same happens vice-versa: your friend shouts at you from ...
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### Do electromagnetic waves produce sound?

Preamble: At 5 AM in the morning, if I sit quietly and listen attentively, I can hear many different noises, on a very high frequency. If I try to isolate the ones that are less noisy, I can clearly ...
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### Is it possible to create an optical medium where sound can travel faster than light?

The speed of light decreases with increase in the density of the optical medium whereas the speed of sound increases with increase in the density of the medium. So is there any possibility to ...
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### Amplitude of a sound wave [closed]

What is the largest displacement of an air molecule for a sound wave of 261.6 Hz with intensity 1 $\frac{W}{m^2}$? I am not sure how to find the energy of a sound wave.
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### Diplacusis - possible to tell which ear is normal?

Diplacusis is a hearing disorder in which the two ears hear the same sound as different pitches. Suppose we know that someone with diplacusis has one normal ear and one ear that is slightly off. Using ...
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### What will limit the speed at which one can play the piano?

I thought about this as a fun question. Suppose we provide a piano player that is limited only by the typical relativistic rules (i.e., hands and fingers cannot move faster the speed of light), so ...
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When deriving the sound wave equation: $${1 \over c^2} {\partial^2 p' \over \partial t^2 }= \Delta^2 p'$$ by linearizing the Euler equation: $$\rho {d v \over dt }= - \nabla p$$ and the continuity ...
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### Crest in Light Doppler Effect

The way it is explained in wiki Doppler effect in sound happens because waves of particles with biggest density called crest hits our eardrums more often if object is moving towards us (increased ...
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### How does superfluid helium interact with ultrasound?

Containing liquid helium in it's superfluid state is of course known to be problematic. Escape by crawling up container walls to 'leak' through solid containers and similar difficulties being a ...
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### Can acoustic waves travel through human body?

If I stand inside a perfect anechoic chamber in front of a unidirectional acoustic waves emitter, I would hear the tone played either using my ears or using a microphone for ultrasonic waves. But what ...
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### What causes loud sound when popping a baloon/bubble?

As I chew my gum, I wonder: when I blow and pop bubbles, what creates the snapping sound? Or similarly, what causes the loud POP when one pops a balloon? Is it the rush of air from inside the pocket ...
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### Optimizing the second, third,… eigenvalues - applications

I'm working on some topics related to spectral optimization as a function of the domain. For example it is known for almost a century (lord Rayleigh and Faber, Krahn) that the shape which minimizes ...
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### Magnitude of tension in a bent string

I understand tension in a straight string as a reaction force to a weight, which acts along the string, ultimately resulting from the attractive forces between the constituent particles of the string. ...
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### Why does hot water and cold water makes different sounds while filling a bucket from a tap

When I fill hot water in a bucket while bathing, there is a difference in the noise it makes compared to cold water. Is there any Relation between temperature of water and sound it makes during ...
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### What experimental evidence shows that sound velocity is the same for all wavelengths?

I'm studying sound waves with Halliday's book, and after reading the whole chapter, one of the questions suggested was: What is the experimental evidence that allows the assumption that the sound ...
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### Physical intuition on vortex sound generation

Whenever a fluid has a nonzero vorticity, it looses some of its energy in a form of sound wave. Formally is this mechanism described by Lighthill's equation or some related model (like e.g. Curle's ...
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### what is the relationship between the diameter and frequency of a driver?

What is the relationship between the diameter of a speaker/woofer, and the frequency it is capable of reproducing?
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### What does a blackbody sound like?

Update: According to this wikipedia article, blackbody radiation is just thermal noise (Johnson–Nyquist noise); if that's what I'm looking for, what does it sound like? If a blackbody has a ...
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### How can one change the virtual position of a sound source with a fixed array of speakers?

I have a question about signal processing: How to make a person, sitting between array of two loudspeakers (one from the left and one from his right), hear the sound that came from both loudspeakers, ...
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### How loud would a sound have to be to be heard around the world?

I'm reading the book Cosmos by Carl Sagan, and in it he states: Striking the Earth's atmosphere, a modest cometary fragment would produce a great radiant fireball and a mighty blast wave, which ...
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### Acoustical wave equation from Hamilton's principle

It is common to show the features and power of the Hamilton's principle by deriving the equation of vibrating string, membrane etc. using this principle. But I have never seen that used for deriving ...
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### Waves and osciilation [closed]

When intensity of sound increases increases to 10 times level of sound increases by 10 decibel why and how the sound intensity is related to sound level
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### What it sounds like when I'm travelling at the speed of sound

totally hypothetical here: lets say a man is playing a song on a guitar and I begin travelling quickly away from the guitar, if I were to reach the speed of sound, what will I hear? (my assumption ...
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### Do sound waves travel before Big Bang?

So I was reading a Scientific American article about how the universe is spreading apart and how it is getting faster. But in the article there was something that baffled be and it was this "Sound ...
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### Why don't choir voices destructively interfere so that we can't hear them?

Sound is propagated by waves. Waves can interfere. Suppose there are two tenors standing next to each other and each singing a continuous middle-C. Will it be the case that some people in the ...
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### Sound wave in a Vacuum

If a Tuning fork was Struck in a Vacuum what happens to the resonant frequency of the fork and the potential sound wave. Does the wave leave the fork?
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### How to detect “noisiness” of sound wave?

Some phonemes like "ssss" are basically white noise. How would you determine which parts of a wave are white noise? From frequency analysis the white noise will have no tones so just using this would ...
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### How to derive end-correction value relationship for open-ended air columns?

According to Young and Freedman's Physics textbook, in open-ended air columns like some woodwind instruments, the position of the displacement antinode extends a tiny amount beyond the end of the ...
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### The Speed of Sound [duplicate]

Just a question about Physics I'm doing at school. If the speed of sound is inversely proportional to the density of a material, why does sound travel faster in solids (it is the most dense). I have ...
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### does the Fresnel approximation apply in the far field?

Most sources I've looked at treat far field diffraction and near field diffraction as separate cases, with the former using the Fraunhofer approximation and the latter the Fresnel approximation. In ...
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### How can a string vibrating in a plane radiate sound?

If a plucked guitar string vibrates in a plane, how are waves produced that travel in all directions? I'd have thought that a vibrating string can only produce waves in its plane of motion.
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### Why are exploding HHO bubbles louder then pure HHO?

We tried my electrolyzer with a friend today, we filled a small bottle with HHO gas, and set it on fire. It was loud but not a big deal, like a firecracker. Then we added some soapy water and created ...
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### Mach Number after Normal Shock

Is there any way that someone can give me more of a conceptual explanation for the fact that the Mach number downstream of a normal shock must be less than or equal to 1? I understand the ...
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### Why are ultrasounds used for producing images of body organs?

Low frequency waves can penetrate better than high frequency waves, then why are high frequency waves used in ultrasounds for sharper images? Similar is the case in detection of flaws in metal blocks....
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### Reverberating sounds?

I know a home where there are two television sets in two different rooms. The TV sets are diametrically opposed to each other. When I move from one sound source of TV one to TV two a phenomenon occurs....
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### Physical interpretation of source term in wave equations

Let me start with an example. If we base our calculations on the Newton's second law without any further mathematical treatment, then our equation describes equilibrium of forces, i.e. it is of the ...
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### How would I calculate the frequency of the sound produced by a bowed glass plate?

I'm working on a project that involves getting a note to sound from a glass plate by bowing its edge with a violin bow. I'm trying to work out exactly what frequency I'll get from a piece of glass of ...
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### What's the relationship between the tension of string and the decay rate of its vibrations?

It seems that the more tension on the string, the more slowly the sound would decay after being plucked. Is there a formula relating the two? How is it derived?
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### Overtones of Bells Over A Distance

The hourly bell tower sound at Indiana University Bloomington sounds like a higher frequency when heard from ~1.4 km away, compared to standing right next to it. Is this effect likely due to the ...
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### Properties of infrasound of our muscles?

I have read, that some animals (like cats) are able to hear other animals (like humans) staying still by percepting infrasound, emmited by their muscles. Is this true? I know, muscles are really ...
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### Pitch and loudness relation

Using an Oscillator in a program, I noticed that the lower and the higher frequencies are less loud than the middle ones. I suspect there is a relation between pitch and loudness but can it be ...
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### Intensity of sound vs Speed of sound

I am finding out the relationship between intensity of sound and speed of sound. To do that, I am using this equation: $$I =\frac{∆P^2_{\rm max}}{2ρv}$$ where ∆P max = Pressure amplitude, I = ...
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### What is the equation of motion for multiple simultaneous pressure waves in a medium? (In the context of stimulated Brillouin scattering)

My overall motivation is to derive the behavior of Brillouin scattering in a birefringent fiber. Brillouin scattering is a nonlinear interaction between light and sound. In classic Brillouin ...
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### In a sound wave, is there rarefactions at both ends?

I was reading my book Physics, For scientists and Engineers, Third Edition, by Randall D. Knight, studying the first chapter on waves. This diagram is provided on page 565: The diagram is easy to ...
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### Sound when traveling faster than sound

I was wondering, if I am running at the speed of sound while playing music on my iPod will I be able to listen to my iPod while running at the speed of sound? or we cant hear anything while running at ...