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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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Resonant frequencies in air filled closed cylinder

I want to calculate the resonant frequencies of a closed cylinder covered with rigid walls. The cylinder is of dimensions: diameter = $1m$, length = $1m$. Would this fundamental mode formula be ...
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Change in pitch on a flute due to blowing at a different angle

Why is it that the location of where the air hits the inside of a tube, the pitch is affected? When playing the flute, directing the air downwards lowers the pitch. Another student suggested that this ...
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Sound waves in different octaves

How do the sound waves compare between different octaves? Why is it that you can play a low c and a c, and they are at different frequencies, but the same tone? An octave above a note is the fourth ...
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How does the green function for the wave equation in three dimensions preserve the ordering of noises between a speaker and a listener

I was provided with the following equation in class for the Green's function of a three dimensional wave equation: However, I am confused as to how this form of the Greens function preserves the ...
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Light propagating through a sound wave

We know that the speed of light depends on the density of the medium it is travelling through. It travels faster through less dense media and slower through more dense media. When we produce sound, a ...
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Is it true that we can speak, sing, and play wind instruments due to the Bernoulli effect? [closed]

Is it true that we can speak, sing and play wind (brass) musical instruments due to the existence of the Bernoulli's Principle ?
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Why does Stirred (rotating) coffee alters cup’s resonance frequency? [duplicate]

I place a spoon in my cup of (dolce gusto lungo) coffee and tap the bottom of the cup with my spoon. It emits a certain (fixed) frequency. However, if I stir the coffee (but not so fast that the ...
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How does acoustic impedance change with frequency of the wave and thickness of the medium?

I read in many posts that the acoustic impedance of a material is usually defined as Z = p*c, where "p" is the density of the material under consideration and "c" is the speed of sound in that ...
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Is there a way to calculate the $Q$-factor?

I’d like to calculate the $Q$-factor for an acoustically resonating object. I’d like to keep the tests to a minimal, none if possible. Is there any way to do this?
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How to calculate the amplitude increase by resonance?

If you know the natural frequency of an object, how would one calculate how much the amplitude increases because of resonance? I would imagine it would depend on the material?
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1answer
46 views

Does the supersonic aircraft feels less air resistance than when it flies with velocity less than sound

When ever I see pictures like this of some object flying at speed greater than sound , I see triangular waves . So I got question in my mind that Do supersonic objects weather its bullet or aircraft ...
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How to find acoustical output of a horn?

If I had a horn or cone that could be written as a function $f(x)$ rotated around the x-axis, how would I calculate the output, knowing the input (intensity, frequency, everything)? I want a way to ...
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Why do popcorns sizzle after popping?

Why do popcorns make a sizzling sound after popping? At first I thought it might be due to moisture, but according to this, that is not the case, as the water present in the corn has already ...
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What does Webster's Horn Equation give?

When you solve the Webster Horn Equation, I've seen in papers that you often get a term $\phi$ which is supposed to represent velocity potential, but I've also seen $P(x)$ which is supposed to be ...
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1answer
37 views

Why normal component of particle velocity must be continuous at boundary?

I have problems for understanding the following: Source: https://mycourses.aalto.fi/pluginfile.php/393850/mod_resource/content/1/Lecture7.pdf Why there would be a vacuum at the boundary? I dont see ...
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Is it possible to find acoustic amplitude at a certain frequency if you are given dBA?

I was wondering how one would find the acoustic amplitude of a sound wave if you knew the dBA value of that sound wave?
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9answers
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If sound is a longitudinal wave, why can we hear it if our ears aren't aligned with the propagation direction?

If a sound wave travels to the right, then the air molecules inside only vibrate left and right, because sound is a longitudinal wave. This is only a one-dimensional motion. If our ears are oriented ...
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1answer
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Is there an equation to relate a glass's frequency to its mass when it's struck with a spoon?

The mass therefore would be changing because I am pouring in water and testing the frequency at different volumes. Obviously as the volume increases the mass increases and the frequency decreases. ...
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Total internal reflection of sound

Does sound experience the total internal reflection from a boundary of two materials, say, aluminum and copper? The Freshnel formulas for light depend on polarization. However, sound typically is not ...
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Do the authors of this PR Letter suggest sound transports mass, or only that it can be a source of gravitation?

Question: Do the authors of this PR Letter suggest sound transports mass, or only that it can be a source of gravitation? The Phys.org article More evidence of sound waves carrying mass says: ...
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3answers
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Can a sound wave begin with rarefaction?

Some digital recording samples (audio files) of recorded acoustic sounds present sound waves which begin with rarefaction. Is this an actual phenomena that can occur or is it a result of sound ...
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1answer
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How loud does a sound need to be to make pressure waves detectable by a camera?

I've seen Veritasium's video that describes how sound can be picked up by a camera by observing small movements of objects sensitive to pressure changes (bag of chips, aluminium foil, paper...). That ...
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If all harmonics are generated by plucking, how does a guitar string produce a pure frequency sound?

A guitar is a plucked instrument and it is played by plucking a string at an off-centre point fixed at two ends. In general, Fourier analysis tells that all harmonics (the resonant frequencies of the ...
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Sound Waves Moving Large Objects?

I recently read an article over using sound to move/levitate objects in mid air. Which is basically using sound to go against/defy gravity. For Many years Physicists have been able to move smaller ...
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2answers
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Why does a metal block make a shrill sound but not a wooden block upon hammering?

When hammered, a metal block makes a shrill sound but not a wooden block of identical shape. Is it that the wooden block vibrates with lesser frequency than the metal block? If so, why is that? Also ...
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Yi's Bell sound and how it relates to temperature?

Yi's Bell is an ancient chinese musical instrument that plays different sound frequencies when its heated than when its in room temperature. My question is Why does that happen? Why does higher body ...
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1answer
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Does speed of sound in of air change if it is enclosed vs. open air?

To calculate the velocity of a pressure wave (sound) in a fluid, I came across the equation c = sqrt(K/p) where K is bulk modulus and p is density. My question is, if density of air stays constant, ...
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Loudspeaker attached to cylinder - effect on speaker SPL?

I have a loudspeaker that is facing into a long cylindrical piece of PVC pipe of length $L$. The loudspeaker is sealed in so that no air can escape around the edges. The pipe is open at the other end. ...
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1answer
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How to calculate acoustic impedance of a megaphone

I'm working on a physics problem that asks how a passive megaphone (simple cone shape) can optimise the transfer of the human voice, compared to not using one at all. I understand that some of this is ...
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Dependence of heat transfer rate on acoustic boundary layer thickness

I have generated a sine wave acoustic signal of constant amplitude and different frequency (i.e. 50Hz to 250Hz). At low frequency i am getting higher evaporation rate. However, at low frequency ...
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2answers
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Loudspeaker attached to cylinder - closed or open?

I have a loudspeaker that is facing into a long cylindrical piece of PVC pipe of length L. The loudspeaker is sealed in so that no air can escape around the edges. The pipe is open at the other end. ...
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1answer
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Why are there these other “harmonics” (violin-specific terminology) in violins?

I've often read explanations of how standing waves form on the string of a violin and their harmonics but there is another phenomenon I've never seen explained: When you play certain notes, musicians ...
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Are sounds louder at night, in the winter? [duplicate]

Surface temperatures of -40C and +40C are not unheard of in habitable areas on Earth. That's a variation of over 30% in density (for a given barometric pressure). Does that mean that for the same ...
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Is this derivation of the Doppler effect for sound waves valid?

I was recently considering how to justify the formula relating to the Doppler effect for sound waves to a group of eleventh grade students who are likely encountering it for the first time. The ...
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2answers
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Why will a guitar string “ring” when I resonate my vocal chords at the same pitch as the string?

From a resting state, a guitar string will begin to ring as I resonate my vocal chords. If I make a fairly loud, and high-frequency "oo" sound at 440hz, then the A string on my guitar begins to ...
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How or where I could experience sonoluminescence in daily life?

Sonoluminescence is a known phenomenon, even if a conclusive explanation for its origin is not given. I wonder if I could ever hear and see sonoluminescence somehow or somewhere in daily life, or if ...
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Where does the sound we hear from short circuits come from?

Title is self explanatory. Whenever I see or watch a short circuit happening, there is always a humming/buzzing sound going on (e.g., the sounds we hear from this short circuit compilation video). ...
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SOUND WAVES :: organ pipes [duplicate]

Why doesn't sound wave escape in a open end pipe, why does it reflect again at open end of organ pipe when it can just move outside.
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3answers
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Sound Waves and the Boltzmann Distribution

Imagine a sound wave traveling linearly in a given direction through a monatomic ideal gas. Based on gas laws and the wave equation, we have that the wave should travel, in that given direction, at a ...
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1answer
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What determines the speed of sound in different mediums?

So, the speed of sound is 340 m/s in air, but it’s much higher in water. I’ve gotten the explanation that the density of a medium determines the speed of sound in the medium. The more dense, the lower ...
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Dopplar Effect with Relative Velocities

My understanding of the classical Doppler effect formula was that the velocities (of the receiver and source) would be relative to the medium in the following formula: However, Wikipedia has an ...
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2answers
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Why do sound waves hang together when traveling at different speeds? (i.e., being refracted)

I've heard that if a cold air layer exists above a warm one, sound may be refracted upward, causing it to miss hearers that otherwise could hear the sound. My understanding (which may not be correct) ...
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3answers
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Why, in an open or half-open pipe, must an open end of a standing sound wave have a pressure of zero?

I believe this question was asked in some form before, but I'm not clear on the answer. If a sound wave must equal air pressure when it exits a tube, why is it possible that at many points after the ...
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1answer
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Can sound with lower frecuency without overtones produce standing wave of higher frequency?

I read that resonance appears if frequencies are equal. What if vocal cord produce only pure tone without harmonics, will voice still have overtones? Or will sound of guitar with only one string ...
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How does one deal with 2 waves to view their beats graphically?

Two tuning forks have frequencies of 480 Hz and 512 Hz respectively. The beat frequency should be the difference, which is 32 Hz. Now I want to see this graphically. I modelled these two waves as ...
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5answers
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If eardrum vibrates when hit, why don't we hear the air in the room that is continuously moving? [duplicate]

The eardrum is pretty thin.Therefore it should be very sensitive to movement.So, why don't we hear the air that is constantly moving.My guess is that the force of air pressure is not enough.Maybe I am ...
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1answer
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Acoustics - tiny ultralow impedance speaker? [closed]

Here's a theoretical question that hopefully someone will be able to shed some light on. Apologies if this is the wrong forum, I figured the electrical engineering community would be more into ...
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2answers
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How can we recognize the sound of two different sources?

Why when 2 or more persons are speaking we can identify the sound source ? How the superposition of the waves make the waves still be heared as they were alone ?
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Why don't I hear beats from a violin when playing two strings at once?

If I use a bow to play two strings at once on a violin or other string instrument, I don't hear beats occurring. Why's that?
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1answer
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Maximum of a sound wave [closed]

I have a question regarding an undergrad problem, and I thought it was going to be easy, but apparently I am missing some key element. The exercise is the question IV-9 of the french Geipi-Polytech ...