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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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Sound problems on frequency [on hold]

Does frequency depend on the number of wavelength the source makes per second? Is it wavelengths? And what is the definition of amplitude?
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Sound emitted by droplets hitting a liquid surface

when a liquid jet (e.g. water) hits a water surface sound may be produced if, due to Plateau Rayleigh instability, the water jet has formed into droplets. But what exactly causes the sound? Is it the ...
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Strange sound of low frequency produced from 2 steel balls

When two steel balls collide, or any metal objects collide, a high frequency sound is produced. However, what was strange is that when I held two metal balls in my hand, and moved them around, it ...
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Derivation of the formula for the fundamental frequency of a stretched string [on hold]

I'm trying to derive the formula: $$f=\frac{1}{2L}\sqrt{\frac{T}{\mu}}$$ but I'm running into trouble with a $\theta$. Taking a string of length $L$ vibrating at the fundamental frequency $f$ we get ...
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1answer
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How does an magnetic resonance guided focused ultrasound (MRgFUS) machine work?

As a medical application, magnetic resonance guided focused ultrasound (MRgFUS), is new I the treatment of some parkinsonian diseases, prostate cancer, none problems, and more. However, I am not sure ...
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Laser creating weird patterns on screen when reflected from a vibrating membrane

Me and a few friends were doing an experiment today in which we took a membrane stretched over a speaker, and a small mirror in the center of the membrane. We reflected a laser off the mirror on a ...
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1answer
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Why can I hear the treble sounds through a speaker, such as on my phone, better than I can with headphones?

I'm not sure if this is related to my hearing loss, or if anyone else has noticed it, but I find it easier to hear higher frequency sounds coming out of a speaker that I hold up against my ear versus ...
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Why is phased array ultrasound imaging only implemented when the propegation material is a liquid or a solid and not a gas?

Underwater sonar imaging, ultrasound medical imaging and solid material imaging for welding checks are all well implemented in systems. But why does it seem impossible to find any information about ...
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How does the thickness of a string affect the frequency?

I've notice that thicker strings have lower frequencies, but is there a specific relationship between theses two?
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1answer
17 views

Feeling sound; frequency and volume

How loud and "low" must a sound be in order for one to feel some physical sensation in response? I've read that below certain frequencies humans can be expected to "feel" sounds in their chests, and I ...
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11 views

Deconstructing harmonics

If I am firing a burner into a cylindrical chamber with a flat rear refractory wall, and we are experiencing constructive amplitude because of a coincidence of sound frequency and vessel length - can ...
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2answers
34 views

Perfect sound-canceling devices

Noise-canceling headphones can reduce a lot of ambient sound, but they are not 100% perfect. (Especially in the human vocal range.) Is there any physical principle preventing the creation of perfect ...
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Chladni Patterns (Length Factor)

I've recently been conducting experiments on the Chladni Plates, testing out how the length of a square Chladni plate (and consequently its area) affects the frequency at which each respective chladni ...
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1answer
33 views

Speed of a transverse wave in a solid medium

Based on the analogy with sound waves, can we say that the speed of a transverse wave in a solid medium is, $$v = \sqrt {\frac {G}{\rho}}$$ Where, $G$ is the shear modulus of elasticity of the medium ...
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1answer
23 views

How does a sound box amplifier work?

I read in a few places that in a guitar for example, the vibrations are passed through the connectors to the wood and the wood with its bigger surface is more efficient as a coupler to the air, ...
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22 views

How do you reckon my mattress works? [closed]

So I have one of those "sleep number" mattresses, made by Select Comfort. Good mattress. It contains two air chambers, and has a pump which can inflate or deflate these air chambers to the desired ...
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1answer
48 views

Diffraction of Sound Waves

We know that Sound waves are Longitudinal waves. It mean that there is pressure difference created when medium particle move. But while diffraction of sound waves 'How will the medium particles move'. ...
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1answer
19 views

Resonant frequencies of a fully closed tube

What is the pattern for resonant frequencies of a tube closed at BOTH ends? The cases for the string, the open tube and the tube closed at one ends are well known.
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1answer
151 views

How does a guitar work?

Here are four different possible ways: The plucked string vibrates longitudinally, vibrating the air around it. This vibrating air then causes the air inside the sound box to vibrate also, which ...
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1answer
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How do we hear harmonics and how does it affect audio fidelity?

First and foremost, do we hear a sound wave as a sum of all the individual harmonics, at the fundamental frequency, or do we hear all the associated harmonics above the fundamental frequency and ...
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does obstacles in front of sound work bidirectional?

If sound S played in point A reaches point B with volume V, after turning it off in point A and turning the same sound S in point B on, does it reach point A with the same volume V regardless of what ...
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1answer
64 views

Why do objects have a Natural Frequency? [closed]

Why should an object even have a natural frequency, why not vibrate at any other frequency? This just sounds nonsensical.
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29 views

How to find the length of a copper pipe, open on both ends, to produce a certain frequency? [duplicate]

For example, to find the length of copper pipe needed to produce a freq. of 1046.5Hz, using the Length-Wavelength relationship of Wavelength = (2/n)*L, I rearranged it to L= λn/2. Problem is, to ...
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1answer
36 views

How to find length of copper pipe needed to produce certain frequency?

I have the basic $f=\frac{v}{\lambda}$. For example: C6 has a frequency around 1046.5 Hz. How do I find the length from this formula?
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1answer
28 views

Why do open-closed cylinders resonate at high input impedance?

According to this paper, open-closed cylinders (clarinets) resonate at maxima of input impedance, while open-open cylinders (flutes) resonate at minima of impedance. Since acoustic impedance is ...
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1answer
48 views

What causes a harmonica note to drop in pitch (AKA bend)?

I understand how I can lower the pitch of any note on my trumpet, regardless of the volume, by slowing the rate of vibrations of my lips. But how is it that I can lower (AKA bend) the pitch of a reed ...
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1answer
21 views

Efficient generation of infrasound

It seems that the most common sources of infrasound are earthquake, tsunami, volcano eruption, etc, which are all large scale behaviors. Why is it difficult for a human to generate infrasound? Is ...
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1answer
64 views

Sound and gravity

How would heavier gravity (or lighter gravity) affect sound in terms of what I hear? For example, say there is a planet that is capable of supporting human life, but it has heavier gravity than ...
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2answers
34 views

Sound Waves concept problem

I am a student . I am trying to understand sound waves. The book which I have got says: In these longitudinal waves there is a phase gap of π/2 between the displacement and pressure waves. If Y= A ...
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How many equivalent continuous sound pressure levels (LAeq) can you fit in a given period?

Anyone familiar with environmental noise will understand the concept of integrating sound level meters -> obtaining a single value sound pressure level with the equivalent energy of the measure time ...
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0answers
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Why do musicians stretch the strings of their string instruments? [closed]

I came across this simple problem:´ A violin string has a density of $\rho=4.0\times 10^{-4}\space Kg\space m^{-1}$ and a length $L=0.33m$, and we want it to vibrate at a frequency $f=660Hz$, what ...
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2answers
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What happens to the pressure time graph when two musical instruments play at the same time?

I'm learning acoustics for the first time and I'm having trouble picturing what the pressure time graph would look like when two instruments play together. https://newt.phys.unsw.edu.au/music/flute/...
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1answer
14 views

Are there any differences between the standing wave diagrams of two non-transposing instruments? [closed]

For example, a cello and a flute are both non-transposing instruments. Thus, they both have harmonics at the same frequencies. Will there be any differences in their pressure time graphs then?
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1answer
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Characteristics of acoustic resonator with a constant gain frequency response

What would be the theoretical characteristics of an acoustic resonator cavity which has a completely flat gain frequency response over 200Hz-3000Hz (Roughly the range of a violin) In other words, ...
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2answers
71 views

At what frequency does a string vibrate?

When a string with fixed ends vibrates (e.g. plucking a guitar string) Fourier Theorem says that the vibration can be expressed as a sum of its normal modes, which are sinusoidal vibrations with ...
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2answers
39 views

Does a string vibrating with hard boundaries contain harmonics of the fundamental frequency?

When the string of a violin is plucked, the resulting sound contains harmonics of the fundamental frequency. Is this an inherent property of a string with hard boundaries vibrating? Does an ideal ...
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0answers
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Does bending a piece of steel change the speed of sound in it?

Specifically, I have a student investigating sound produced in a helical spring (slinky) when struck. When it is struck it produces a sound that changes in pitch - from very high to quite low. Also, a ...
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1answer
53 views

Sound wave equation: Neumann boundary conditions

In this paper it's described the solution of the damped wave equation in cylindrical coordinates $$ \nabla^2\left(c^2\rho_1+\nu\frac{\partial\rho_1}{\partial t}\right)-\frac{\partial^2\rho_1}{\...
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2answers
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How much energy is wasted by a noisy refrigerator?

I recently bought a new refrigerator for my kitchen. The feet are adjustable but I've been lazy. Whenever the motor runs and the feet aren't all touching the floor there is a loud buzzing noise. As ...
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2answers
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Which book would you recommend for a dummy wanting to start studying acoustics, out of interest?

I've been very into acoustics lately, specifically the harmonic series. I find it fascinating how the harmonic series works as a sort of guideline to harmony, and how we base tuning systems on trying ...
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2answers
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Sound, Resonance tube experiment [duplicate]

Why surface of water behaves as a denser medium inspite of the fact speed of sound is greater in water than in air as seen in case of Resonance tube. To achieve resonance again we lower the level of ...
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0answers
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What are the specific heats of Dysprosium in its gas phase?

What are the specific heats of Dysprosium in its gas phase? The handbook of chemistry and physics [1], is a single volume of 1500 pages containing all the information an experimentalist would need ...
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1answer
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Why are C, G and C all played open on the trumpet?

Why are C, G and C all played open on the trumpet? I would expect C, F# and C to be produced by adjusting embouchure as they're evenly each a half octave apart. What am I missing?
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5answers
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Why can we distinguish different pitches in a chord but not different hues of light?

In music, when two or more pitches are played together at the same time, they form a chord. If each pitch has a corresponding wave frequency (a pure, or fundamental, tone), the pitches played together ...
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1answer
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Interesting speed of sound observation

I just came by a table in the Class 11 Physics NCERT textbook, listing speeds of sound in different media. Vulcanised rubber has an unusually low speed of sound $54\ \mathrm{m}/\mathrm{s}$ as compared ...
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0answers
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What attributes determine the sound made by colliding objects? [duplicate]

Simple question, probably very complicated but fascinating answer: If you whack something with a stick, the collision will produce a sound. The quality of the sound however will vary greatly with... ...
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1answer
39 views

What is the error propagation in an FFT (Fast Fourier Transform)?

I use an insert FFT graph feature on a program called logger pro. If I have the uncertainty of my input data, can I know what the uncertainty of the FFT computation will be?
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1answer
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Why does a sound wave on encountering a low pressure region gets reflected with a “phase change of π”?

I am particularly concerned with the reason for phase change of π. This is observed in organ pipes at their open ends. The waves on encountering the open atmosphere(low pressure region) reflects back ...
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1answer
61 views

Where do pure tones occur in nature, besides harmonics?

When you sound a tuning fork, you hear an pure tone/sine wave of usually 440Hz. Yesterday, I tried hitting a table knife made entirely from stainless steel against a grapefruit. When I held it up to ...
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1answer
469 views

How do we know the Earth's core is Molten with Seismology?

My current knowledge about how the core of the earth was discovered is the observation made from non returning/reflecting sonar signal when sent to deeper depths through the earth's crust/mantle. How ...