All Questions

1
vote
3answers
86 views

Initial conditions for wave equation

One of the common initial conditions given for the wave equation, $$\frac{\partial^2 p}{\partial t^2} - \nabla^2 p = 0,$$ is $p(\overline{x},t=0) =0$ and $p^\prime (\overline{x},t=0) =0$. What is ...
0
votes
0answers
46 views

What does a negative end correction mean?

I was asked this question in one of my tests: "In an experiment to measure speed of sound by a resonating column a tuning fork of frequency 500 Hz is used. The length of air in the column is varied ...
1
vote
1answer
46 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 ...
1
vote
0answers
24 views

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.
4
votes
3answers
86 views

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 ...
1
vote
1answer
78 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}{\...
2
votes
1answer
49 views

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 ...
1
vote
1answer
1k views

Why are there only odd numbered harmonics in one closed end resonant tube? [closed]

Why do we only have odd numbered harmonics at one-end closed tubes, however, if we do a frequency spectrum we have some periodic spikes between the odd harmonic spikes, just like the picture below ...
4
votes
1answer
244 views

Open-open pipe standing waves

What is the physical explanation for how a travelling wave sent down an open-open end pipe reflect from the ends (even though they are open) to form a standing wave?
2
votes
1answer
103 views

Why are the nodes of an open tubular bell located at .224*L instead of .25*L?

Say that we have a tube of length $L$. In the tube, there is a standing wave of wavelength $\lambda$. Then, $L=\lambda$. $\hspace{2.5cm}$ In the above diagram, the wave's amplitude is highest at ...
2
votes
0answers
48 views

How do waves get reflected at open end of an organ pipe? [duplicate]

Inside and outside of an open organ pipe usually medium used to be same (if i am not wrong) i.e Air, so in order to get standing wave reflection of wave is needed ( opp.in direction nd of same ...
0
votes
2answers
287 views

Why does energy loss cause end corrections?

Several people have said that end corrections occur because of acoustic radiation or something similar, where energy is used in vibrating the air outside the pipe. How exactly does energy loss cause ...
7
votes
2answers
863 views

Intuitive Cause for End Corrections

I have looked for an intuitive description for the reasons for end corrections. I find most of them with mathematics far beyond my level (high school). I found two sites that attempted to explain it, ...
1
vote
1answer
874 views

How is the relationship between the end correction and the pipe diameter related to acoustic impedance?

I know that Levine and Schwinger calculated the exact value of the end correction by doing something with the acoustic impedance but I don't understand their calculations. I've looked at paisanco's ...
2
votes
1answer
753 views

Why does the Neumann boundary condition represent no flux?

I have heard that the Neumann boundary condition $$ \frac{\partial p}{\partial n} = 0, $$ for the acoustic pressure field in the Helmholtz equation in acoustic wave is related to flux. But we normally ...
1
vote
0answers
41 views

What is happening physically when we vary the $\alpha$ in the impedance boundary condition $u + \alpha \frac{\partial u}{\partial n} = 0$?

Say are considering acoustic waves in a domain $D$ filled with water and with an impedance boundary condition $$ u + \alpha \frac{\partial u}{\partial n} = 0, \quad x \in \partial D, $$ where $\alpha ...
1
vote
0answers
30 views

How can wave propagation in a solid-fluid problem be modelled, and in particular how are transmission boundary conditions handled?

When dealing with wave propagation problems such as electromagnetic waves passing from one medium to another we set up boundary conditions to ensure the field is continuous and the flux is continuous ...
0
votes
2answers
280 views

Justification for acoustic wave equation boundary conditions

In analyzing the standing acoustic waves produced by a wind instrument, one usually assumes that the openings of the instrument are antinodes of the acoustic wave (as depicted below). What is the ...
1
vote
1answer
130 views

Sound wave equation in 3D closed Box

We have the sound wave equation $\Delta p - \frac{1}{v^2} \frac{d^2}{dt^2} p = 0$ in a closed Box. So we got Dirichlet boundary conditions and I can combine the solution for the 1D case to a 3D ...
7
votes
2answers
2k views

Physically, why are high sound frequencies more easily absorbed than low sound frequencies?

If someone is playing music in a room, outside the room you generally hear a more pronounced reduction in high frequencies, compared to low. I know that sound is most easily absorbed by a material ...
1
vote
1answer
288 views

How do sound absorbing materials work?

Some materials like fibreglass are really good at absorbing sound, aren't they ? (not blocking sound, as mentioned here.) Sound propagates when particles oscillate. But what happens to these ...
3
votes
1answer
125 views

Do reflection and transmission coefficients for waves correspond to Neumann and Dirichlet boundary conditions at the interface between two mediums?

Suppose we are dealing with wave propagation in the frequency domain, that is, wave propagation governed by the Helmholtz equation. How do reflection and transmission coefficients for waves correspond ...
0
votes
1answer
76 views

Differences between Dirichlet boundary conditions in the case of acoustic waves and electric potentials?

If we have a an acoustic wave $u$ governed by the Helmholtz equation on the interval $[0, 1]$ then a Dirichlet boundary condition $$u(x) |_{x = 1} = 0,$$ means that the wave goes becomes zero at the ...
12
votes
3answers
10k views

Pressure standing wave nodes at the end of the open side of a tube

I do not understand why standing sound waves can be formed in a one-side or two-side open tube. Consider a one-side open tube. In particular how does the reflection of the wave at the open end occur? ...
1
vote
1answer
420 views

Can you have a problem with a Dirichlet boundary condition but with waves that reflect off the boundary?

Say we are looking for a solution to the Helmholtz equation $$(\Delta + k^2) u = 0,$$ in in the upper half space ($y > 0$) in 2D with a Dirichlet boundary condition on the $x$-axis, that is, $u(x, ...
5
votes
1answer
827 views

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 ...
3
votes
1answer
501 views

Where exactly is the antinode of an air column with open-closed boundary conditions?

Suppose that I have an air column with closed-open boundary condition. The air pressure at the open end of the tube is constrained to match the atmospheric pressure of the surrounding air. Therefore,...
0
votes
1answer
385 views

Reflection of Sound wave (Pressure Wave)

I want to study about the phenomenon of reflection of pressure waves as in an open ended organ pipe. Please suggest a suitable resource? I know about the harmonics in a stretched string and I can use ...
1
vote
1answer
159 views

Zero stress boundary conditions for the acoustic wave function

When is it appropriate to use zero normal stress boundary conditions when solving the acoustic wave equation. That is when the pressure is equal to zero.
4
votes
3answers
3k views

Question on open organ pipe

Although open organ pipe is open on both ends, how standing waves are produced in a open organ pipe. Can someone explain with more clarity?
2
votes
2answers
985 views

What is the phase shift incurred by a sound wave as a result of reflection?

While studying waves I read the fact that a sound wave gets shifted by $\pi$ as a result of reflection against a surface. But I am unable to prove that fact. Assuming the interface to be a node I can ...
2
votes
1answer
2k views

Reflection of sound waves

I was doing a physics experiment, and i encountered a question which i couldnt answer. The experiment was about using a radar technique to measure the speed of sound. The apparatus was a plastic tube ...
6
votes
1answer
751 views

Why does the echo for soundwaves hitting a vacuum come back out of phase? [duplicate]

Possible Duplicate: Phase shift of 180 degrees on reflection from optically denser medium I've read in a physics book for musicians that, when a soundwave hits a near-solid object, it generates ...
4
votes
2answers
16k views

Reflection of sound waves from the open end of an organ pipe & relationship b/w nodes & pressure [duplicate]

We know that standing waves are created when any wave traveling along the medium will reflect back when they reach the end. But in an open organ pipe, there is nothing to oppose the wave and reflect ...
1
vote
1answer
1k views

Open Ended/ Close Ended instruments?

Close ended instruments have twice the wavelength, because the wave must travel twice the distance to repeat itself. Why must a wave reach a lower density medium (air in this case) to repeat? When ...
2
votes
1answer
421 views

Singing: Resonance body open-closed or closed-closed?

Googling yields contradictory results, so here my question: When I sing, my vocal chords vibrate, but my whole body is the resonance body, right? So I would say that when I think about standing waves ...