Acoustic Definition and 150 Threads

I would like to be sure about one case of the use of Doppler effect with sound waves. If the medium (in the case of sound air) is moving, but there is no relative motion between the observer and the source there is no Doppler effect at all. (And the absence of relative motion is...

Hello everyone, I would like to start playing around with acoustic levitation. Apologies if this is the wrong sub-forum... I psoted in General, as I am not sure where the best place would be for this. My question: What equipment would be needed to start a simple acoustic levitation? I have no...

Homework Statement A source emits a very brief sound signal. A receiver ##A## moves along the ##x## axis with a varying velocity such that it receives constantly the echo from the reflecting wall. Find ##v_A## as a function of the position ##x##, knowing the distance ##D## and the speed of...

Homework Statement You have a device that can measure sound waves only if the frequency of the wave is in the range ##0.8 kHz- 20 kHz##. You have a whistle that produces sound waves at ##21.5kHz##. You ride a bike moving away from a wall, at the same time you blow the whistle and hold the...

The beats frequency heard from the interference of two sound waves with frequencies ##f_1## and ##f_2## is $$\nu=|f_1-f_2|$$ Nevertheless the frequency of the resulting wave is not ##\nu## but the mean value of the two frequencies $$f_{resulting}=\frac{f_1+f_2}{2}$$ As far as I understood...

Homework Statement I need this to find the the reflective coefficient and multiply this by 100 to find the percentage of original energy reflected back however i cannot find the acoustic impedance of wool no matter how hard i try. Homework Equations Im using the reflective coefficient formula...

What is the physical meaning of acoustic and optical branches in phonons dispersion curves ?

If we know the max. pressure (p) is 2.5 MPa and T = 20 C. Peak intensity, I = p^2 / rho * c where rho = density of water: 0.9982E03 kg/m^3 and c = speed of sound in water: 1482.3 m/s at 20 C I = (2.5E06 [Pa])^2 / 1.4796E06 [kg/m^2/s] = 4.2241E06 W/m^2 Is this correct?

Hello friends. My question consists two parts, 1-What is the difference between an optical and an acoustic phonon? 1-What are the conditions by which we can decide the type of phonon i.e optical or acoustic phonon ? Hope to get the reply soon.

Hello guys, Consider a partially filled tank with water where the acoustic field can be described by the Helmholtz equation. The boundary condition at the water surface would be \frac{∂p}{∂\vec{n}} = -j\rho_0\omega\frac{p}{Z} where Z is the impedance of the water surface. What would be...

Hi, I am just trying to understand the output of a sound spectrum analyzer. There are three dimensions 1) Time 2) Frequency 3) Volume (db) I am confused about few things here: 1) How should I perceive the volume dimension here? 2) Why are the db values negative here and w.r.t what reference...

I found a fast solenoid valve lying around (~1ms rise time) so I thought it would be fun to hook up to a compressed air line and use to generate some really loud bass. I hooked it up to a function generator and air supply only to find that it was disappointingly quiet (well not quiet, but...

I have an impedance tube and it gives me the magnitude (dB) and phase (phase) of a signaa. So does that mean the complex pressure at that point is simply the [Magnitude] +i[Phase Value]? Does I need to change the units at all?

Hello everyone; My question is regarding to velocity effect on transducer diaphragm. When fluid flow is acting to differential pressure transducer's diaphragm, the diaphragm is osculating(vibrating) and there will be fluid flow which is transverse(opposite flow,back flow) to normal fluid flow...

Homework Statement Derive from the formulas ##\frac{D^\pm}{Dt}(u \pm F) = 0## where ##\frac{D^\pm}{Dt} = \frac{\partial}{dt} + ( u \pm c) \frac{\partial}{\partial x}## the one-dimensional wave equation in the acoustical limit. \begin{cases} u << c\\ c \approx c0 = const\\ F =...

How do BAO help us measure dark energy? thank you for all the help PF members give in the cosmology forum.

In particular, something focused on the acoustics of musical instruments and ideally with a bit of the physics behind playing techniques. In terms of my preparation, I've completed math up through linear algebra, ODEs and multivariable calculus. I've also completed all of the "core"...

I found this forum while searching for information on William Close Earth Harp. There is a closed thread here on the subject though it seems some are still in doubt one could tease sound from a long string device. While William created his Earth Harp in 1999, Ellen Fullman created her long...

Hi, I was just wondering why, when the acoustic impedance mismatch is so high between two boundaries at an interface, most of the ultrasound is reflected back. I was just wondering why this happens which I can't seem to find much of an answer to. The only thing I can think of is refraction and...

While the sound waves travel in a medium, let's say a fluid, what is the difference between fluid pressure and acoustic pressure ? Are these entities same?

Dear All, Can someone give me an intuitive idea of the acoustic radiation force. I have read from a paper that the acoustic radiation force generated by a standing acoustic wave is larger when the size of particle is smaller than the acoustic wavelength as compared to the case when size >...

I've been doing some research on how to create cheap yet effective acoustic paneling for the purpose of blocking out sounds from the bedroom wall in my apartment. The walls are so "thin" that I can hear my neighbor snoring. I'd also not like my neighbor hearing me giggity. The best thing I've...

I'm having some trouble understand this correctly, so I was hoping someone could enlighten me a bit :) Okay, so in the early Universe most of the hydrogen and helium was formed, and then kept in equilibrium, and ionized via photons. So we have a plasma of baryonic matter, including dark matter...

Hello All, I would like to know why do we multiply the complex conjugate of velocity (not just the velocity) with the complex pressure to obtain the complex acoustic intensity. Could someone please help me with this? Regards, Radel...

Good day everyone. I would like to know about the lower limit of the frequency range of active acoustic phonon modes. Textbooks say it can reach zero. But I am curious about whether it can be very small, such as 1 micro volt or the like. Would a phonon mode of so small energy be of any...

Hi, I am not a native English Speaker, so some words might not be appropriately used below, but I will try my best to explain what I was thinking about. In general, I have never learned how acoustic waves emerge microscopically. The application of the theoretical knowledge I acquired was always...

Hi there. I've been looking around for a decent physical explanation of the differences in the phase relationships between acoustic pressure and particle velocity in different types of waves. Mathematical analyses abound, e.g...

Homework Statement Assume that the wavelength of acoustic waves in an organ pipe is long relative to the width of the pipe so that the acoustic waves are one-dimensional (they travel only lengthwise in the pipe). Therefore, the equation governing the pressure in the wave is: ∂2p/∂t2-c2*∂2p/∂x2...

Hi, I am just trying to understand the connection between these two things. As far as I understand it: BAO - Before decoupling the baryons were in thermal equilibrium with photons and as a result this gave rise to a pressure force. But given in regions of high dark matter density baryons are...

Acoustic Wave Velocities in Brillouin Zone - Phonon Spectrum of Ge Homework Statement Acoustic Wave Velocities in Brillouin Zone - Phonon Spectrum Diagram The exact problem I'm stuck on is Q3c on this exam paper. I have included an image of the problem below. I haven't had any trouble up...

My textbook says I'm confused by this, because isn't a standing wave caused by reflection of the waves once it has hit the end of the tube and reflects backwards. How can sound waves be reflected from the open air? Thank you for taking the time to answer. :)

http://sploid.gizmodo.com/amazing-scientists-make-things-fly-around-in-space-usi-1492880964 I wanted to ask is there a specific reason for the completely horizontal X shape of the levitated particles. If we already have such precise control over the standing waves, couldn't it be possible...

Greetings PFers, I'm working on a project where I need to focus powdered that is being blown through a tube. I would like to discuss the option of using acoustic focusing to guide the particles to the axis of the tube to prevent the particles from contacting the tube inside diameter. There...

Basically phonons in crystals can either be acoustic or optical according to my book. But then it stresses that a necessary condition for this to hold is that the crystal has more than atom per primitive basis. The optical modes are then when neighbouring atoms oscillate out of phase (i.e. no...

Acoustic Observatory -- Low-Cost I have built what I call an Atmospheric Acoustic Observatory. It could also be thought of as a high-resolution barometer. There's a write-up on it at http://www.comfortlight.com/baro.htm. It is simple in principle, and it cost only about $50 for the main...

Acoustic Observatory -- Low-Cost Check out my Acoustic Observatory It uses well-known and obvious principles of operation to "see" thunder at great distances. It cost about $50 to build, including the red laser diode -- but not including the front surface mirror which has been lying around my...

Hi, I am confusing if capillary-gravity waves (Faraday waves) belong to a type of acoustic waves stricto sensu? What's the difference between Faraday standing waves and acoustic standing waves (interference) at the the air-liquid interface. Thanks harmonyU

Homework Statement Atmospheric pressure is 101 kPa. Compute the acoustic pressure that corresponds to the threshold of pain for the ear. What percentage of atmospheric pressure is this? Homework Equations L=20log(P/Po) Po is a constant = 2x 10-5 threshold of pain for the...

Dear all, many people refer to the CMB anisotropy picture by WMAP or Plack and call it acoustic waves. I thought there is the anisotropy of the CMB radiation plotted, what exactly can I imagine to be the acoustic wave of it? Secondly, what exactly is plotted n the famous plot where the...

Arnold, an in interview with Lui in Notices of the AMS, Volume 44, no 4, p432 says: "It is a far-reaching generalization of the well-known fact of the impossibility of acoustic communication in the even-dimensional spaces (for instance, in the “plane” world), while in our three-dimensional...

I'm doing a research paper about electronic wireless communication using sound. I've got a few reference regarding its use in underwater networks, networking within a body in a medical context, and one regarding communicating information through a steel wall (such as a sealed pressure vessel)...

I find that the acoustic impedance is given by Z= Pressure/ Velocity I read that the acoustic impedance of a plane propagating wave is given by Z = ρ0c. What is ρ0 and c? Thanks a lot

What is acoustic length in a pipe/tube? On a physics lab, the lab write up mentions it but it doesn't explain what it is. I know it's give by L = λ/4 and higher ones will be odd multiples of the first one. But what does this actually mean and what is it for? I looked it up but couldn't find any...

I'm trying to classify materials based on the reflected acoustic wave they produce. One transducer sends out an ultrasonic pulse to the material of interest and another transducer picks up the reflected waveform. Some of the wave is transmitted thru the material and reflected off of the...

Greetings, I've been looking for a way to create a microphone capable of picking up high frequencies (up to about 100kHz). Electrets don't tend to go that high and piezo crystals even detuned will only give a limited band. I had the idea of bouncing a laser off a sheet of reflective...

I am working on an animal vocalization study and I need a clarification about acoustic impedance. All of the sources I have gone to are a bit too technical for me, so if you would be so kind to answer my question I would be very grateful! My question is this: What happens to a sound in high...

I'd like to learn more about acoustic analysis of musical instruments, but I have no idea where to even start. I've taken some acoustics courses and some fluid dynamics courses as well as structural vibrations. What I'd like to do is model an instrument and then have a numerically predicted...

I am considering applying spray-on acoustic/popcorn ceilings to reduce the noise level in my house. I haven't found any data supporting that popcorn ceiling reduce noise level. I am looking for data, physics, experiments, and tools to help me figure this out. I asked this question at...

I came across an article in American Journal of Physics recently that describes how to build an acoustic radar by transmitting a carrier modulated with pseudo-noise code through a speaker and simultaneously receiving the reflection with a directional microphone. One then does some signal...

We know that air molecules are subjected to random motion in different directions. A sound wave is a push toward these molecules to make a wave front to make them expand or contract in groups so that we can hear a voice message in our ears. The question is that what happens when different...