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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Does special relativity also imply that speed of sound is constant for all observers irrespective of their relative motion?
I am reading lec15 The Special Theory of Relativity from the Feynman lectures.
Poincaré made the following statement of the principle of relativity: “According to the principle of relativity, the ...
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Why do airplanes sound louder when its cloudier?
I am from India, and now its monsoon season. Typically, during this time, the sky is filled with dark rain clouds. Me, along with several of my friends, have observed from childhood that the planes ...
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Can taut membranes and strings that are clamped at both ends propagate non-standing waves?
I'm going through an introductory course in acoustics and I'm struggling with the intuition behind standing waves.
When deriving solutions to the various wave equations we usually impose a boundary ...
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Lamb wave derivation: Elastic wave propagation in a thin sheet
I am trying to follow the derivation for the phase velocity for elastic waves with large wavelengths compared to sheet thickness, propagating in a floating ice sheet, as described in Propagation of ...
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Which better conducts vibration: wood or metal?
For some reason I can't get a definitive answer on this. My bedroom is on top of a garage, and every time the garage door opens/closes, the old garage opener that's positioned on the ceiling vibrates ...
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Is the Doppler Effect for sound waves with a moving source due to the fact that the wave speed is independent of the source?
The Doppler Effect is typically formulated as follows:
$$f' = \dfrac{v \pm v_o}{v \mp v_s} \cdot f$$
The reason for the frequency increasing for observer moving towards source seems clear enough. It ...
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An echo that sounds for years?
How exactly should I understand United Airlines Flight 2860's description and English Wikipedia? Namely, last sentence of the fourth chapter of the summary:
The "echo" of the crash could be ...
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Physical basis of "forced harmonics" on a violin
I have recently learnt of a somewhat novel violin technique, sometimes known as "forced harmonics", where, in a physicist's terms, instead of the normal N=1 stationary wave (fundamental mode)...
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Sound Attenuation and Loss Factor
I am currently trying to explain the reasons for my sound transmission loss for my material selection and design. I am using polymers of different depths and currently in my model I'm considering ...
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How can sound travel as a transverse wave?
We know that sound travels by each previous particle transferring its energy to the next successive particle.
We also know that transverse waves are those waves in which particles move about their ...
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Since waves are abstractions, does it even make sense to ask whether light is a wave? [closed]
All waves transmit energy.
Water Waves
Let's say you're in the middle of a calm pond and you start moving your hand up and down. Transverse "waves" are generated, and they propagate ...
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Can we trust our ears in speech recognition in an audio file? [closed]
Can we trust our ears in speech recognition in an audio file?
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How do shock waves reflect?
As seen in this picture, an oblique shock was reflected off of a solid wall. I understand that the flow has to turn to continue the shock, but how does this work when it gets to a wall?
What happens ...
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Why is transfer of heat very slow as compared to transfer of sound in solids?
If I heat a one-meter long iron rod at one end, the heat takes several seconds to reach the other end, while sound takes fractions of a second. Why is it so?
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What is the pitch or air flow constant of a whistle?
I am making a whistle capable of making any sound and/or frequency based on a specific air flow, but despite my personal goal, What is the pitch or air flow constant of a whistle?
I mean to express, ...
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Interpreting the magnitude of vectorial phasors
In fields of physics such as acoustics and electromagnetism, we often deal with physical quantities that are both vectorial and oscillating. These can be represented as vectorial phasors,
$$
\vec{b}(t)...
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Calculating the amplitude of a vibration based on the sound intensity
I am stuck on this problem.
Assume I have a speaker generating a single frequency tone, $f_s = 100$ Hz, and I want to calculate the amplitude of the speaker vibration $A_s$. I measure the sound ...
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Confusion about sound intensity
I think there is something fundamental I'm not understanding about sound intensity.
I have a small speaker at home, roughly 10cm square and the specs state it has 3 W output. That equates to 300 W/m^2 ...
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What is the difference between loudness, amplitude and volume?
i'm confused because some websites I've seen they are not the same, while my textbook says they're the same, and I'm trying to find the distinction between amplitude, loudness and volume.
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Is simple sound transmission in matter normally 100% efficient or is there "leakage" to heat even when there is no damage or destruction of medium
Specifically I was wondering for instance in a perfect gas or real gas or water or steel does the medium absorb some sound as perhaps thermal energy, or can it always travel without losses through the ...
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Doppler shift from a moving reflector and source if only the relative velocity is known?
Suppose there is a device which is producing and listening to sound (sonar), a reflector is moving with respect to device and the velocity of reflector and device with respect to the air is not known, ...
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Why is there a relationship between thickness of an acoustic panel and the sound frequencies it absorbs?
When it comes to acoustic panels (usually in context of sound-proofing a room), I here it often than you're gonna need very think panels to absorb low frequencies. I don't understand why the thickness ...
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Doubling up on Ear Protection NRR Equation
I'm planning to go to shooting ranges soon, and am looking for ear protection.
Let's say that I get an earmuff with a noise rating reduction (NRR) of $X\ \textrm{dB}$ and earplugs with $Y\ \textrm{dB}$...
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How exactly does a seashell make the humming sound?
My little brother asked me where the ocean-like sounds came from inside of a sea shell. I told him that the air trapped inside the shell vibrates, making a sound. But then he asked me why the air had ...
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"Friction at a contact point", rubber-band experiment
I was working on some practice problems in my book, and the question was to describe all the energy conversions that happens when a person pulls on a rubber band and hits it on a board (any type of ...
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Derivation of the formula for intensity of sound wave [duplicate]
I was trying to derive the formula for finding the intensity of the sound wave, after deriving it in my way i am missing a factor of 2 in the formula, Can I know what I am doing wrong ?
Here is my ...
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Acoustic Field Theory examples and resources
Does anyone know of any good resources to study Acoustic Field Theory? Mainly focused on reflection and refraction of acoustic waves. I currently have online versions of B.A. Auld's book on Acoustic ...
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Local Maxima in a Dispersion Curve
Hello I programmed a dispersion curve and plotted the phase velocity.
I am noticing that for one of my modes (the S2 mode) my phase velocity reaches a maxima and then decreases. Is this a physical ...
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Sound Timing: Stationary vs. Moving Source - Who Wins?
Case - 1: A stationary source emits sound and an observer stationary is at 'd' distance apart.
Case - 2: A moving source emits sound when an stationary observer is at 'd' distance apart.
Will in both ...
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Feynman claimed "The ear is not very sensitive to the relative phases of the harmonics." Is that true?
In The Feynman Lectures on Physics, Dr. Richard Feynman claimed that the ear (I assume he meant the human ear) is not sensitive to the relative phases of harmonics.
However, I was asked to test ...
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Temporal absorption coefficient from complex wavenumber
A complex wavenumber $k=\beta-i\alpha$ can be defined, that when substituted into a time-harmonic solution $e^{i(\omega t - kx)}$ yields $$e^{-\alpha x}e^{i(\omega t - \beta x)}$$
The first negative ...
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Is sound louder in a solid compared to air?
Consider this experiment, where it is shown that the sound of the metronome is louder when you hold the acoustic sensor directly towards the table. Many explanations in the internet argue that it is ...
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Question about waves in a fixed string
consider a string that is fixed at both ends. This string is connected to a metal stick. When I hit the metal stick, sound waves (longitudinal and transversal ?) will propagate trough the metal and ...
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Amplitude based on number of equal sources
A homework problem states the following:
In a urban road with a lot of traffic the sound level produced by a flow of a 100 cars per minute during the day is $B_1 = 80$ dB. Calculate the sound level $...
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Can absolute silence exist and how are thermal and quantum noise a limit? [closed]
For my exam, I must answer the question: can absolute silence exist? While doing research, I obviously heard about noises internal to our body and noises external to our environment but I also heard ...
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Can active sonar detect objects by "fluorescence" in a different frequency from the original pulse?
Just now a bumblebee flew past me (more than a meter away), and for a moment its prominent droning sound seemed to make a vibration on my face I could feel. It made me wonder: consider a bumblebee, ...
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Changing the frequency of the tuning forks
I just bought some tuning forks with frequencies of 128 Hz and 512 Hz. However, when I tested them using an app, their frequencies turned out to be lower than the specified values. How can I increase ...
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How does flute work?
I started learning flute a few months ago. Here in India you can buy two types of flute hindustani and carnatic. Hindustani flute has a simple acoustics.
Lenth is inversely proportional to frequency.
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How does a guitar string produce sound?
I'm curious about the mechanism of a guitar producing sound. Of course, I know once a string is plucked it vibrates in a superposition of several harmonics, but what I don't know is what happens next. ...
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Why is Acoustic Impedance Proportional to the Speed of Sound if It Measures Difficulty of Wave Propagation?
I am studying Advanced Level Physics and I am confused about the following entry in my notes:
If acoustic impedance is a "measure of how difficult it is for an acoustic wave to travel through ...
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Conceptual doubts about Chladni Plates
For a divulgative project that I'm working on, we've built a two Chladni Plates a square and a circular one. The idea is to do a demonstration in front of high schoolers, accompanied by an explanation ...
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Is there any deeper explanation behind this simple acoustic experiment?
my question is a bit inconvenient but let me explain:
I recently saw an experiment for primary school where two strings are attended to a coat hanger (see here: https://www.youtube.com/watch?v=...
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How to Measure the depth of a Hole by Dropping a Rock? [closed]
Let's say I have a rock and a stopwatch.
I am standing on the edge of a deep hole or canyon, and can see the bottom.
How would I go about measuring the depth of the hole?
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Ultrasonic pulse in tube produces two reflections
I have an interesting problem which after much research I can not find any answers.
I have an ultrasonic transducer sending a $500 \,\mu\text{S}$ $48 \,\text{kHz}$ pulse into a clean $20 \,\text{mm}$ ...
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Problem with calculating the variance of different sounds
Problem:
In a layered crystal with weak connections between layers, the dispersion law of acoustic backgrounds has the form
$$\omega _1=s_1q_{||}, \ \ \omega _2=s_1q_{||}, \ \ \omega _3=Sq^2_{||},$$
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Question about Proportionality in Sound Equation (Pressure and Displacement Amplitude)
Why is intensity in terms of pressure amplitude inversely proportional to density and velocity:
$I=\frac{\Delta p_\text{max}^2}{2\rho v}$,
while in terms of displacement amplitude, it is proportional ...
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We know that people can hear whether the water is hot or cold from the act of pouring, but have we ever considered the shape and material of the cup? [closed]
We know that one can hear whether water is hot or cold from the act of pouring, which is related to the viscosity of the water, the column of air inside the container, and the overall vibration of the ...
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Validity of approximations in the derivation of sound waves from Newton's laws
In deriving the wave equation describing the displacement of air in the atmosphere usually some assumptions about the displacement function $\chi(x,t)$ are made. For example Feynman says:
Now in ...
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Confusion between two equations for sound intensity
The definition of sound intensity is $I=P/S$, where $P$ is the power generated by the wave source and $S$ is the area over which the energy is transferred. Assuming conservation of mechanical energy ...
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How does the chain rule work in sound wave analysis using fluid mechanics? $\tfrac{d x}{dt}\neq v$?
Context:
I am reading Landau & Lifshitz's book on Fluid mechanics. Specifically its section on Sound waves.
In section 101, the book's authors discuss about nonlinear traveling waves in one ...
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