New answers tagged

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Echo and Reverberation are both types reflected sound. Echo typically refers to a single reflection that's from a surface that's large compared to the wave length and that produces a specular reflection (in contrast to a diffuse reflection). It creates a visible peak in the impulse response that's concentrated around a single point in time and doesn't ...


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Its like warm and hot. They are pretty much the same. Reverberation is the echo you get in a small enclosed space. Echo is all echoes.


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The expression is independent of $\sigma$ and therefore there is no higher harmonics growth etc., only decay of them. I think your exponents have $\sigma$ in them through the $x$ terms, e.g., $$ e^{-n^{2} \alpha \ x} = e^{-n^{2} \alpha \ \bar{x} \ \sigma} = e^{-n^{2} \frac{\sigma}{\Gamma}} $$ One could also find $\sigma$ from $\Gamma = \tfrac{\sigma \ ...


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If you are to say: ignore that there exists no medium for the sound wave to travel and calculate the time it would take for a sound wave in some medium (air, for instance) to travel that distance. It would be calculated as follows: Speed of sound in air is $|v| = 343 \frac{m}{s}$ the distance between the moon and earth is about $384.4 \times 10^6$ meters. So ...


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The problem is that your point view is too "mathematical". No offence, but every acoustician would jump to the ceiling hearing "one can just erase all const, they do not change anything". Oh, they do $-$ very much! Since one of them is the sound speed... But I get it, you solve that as a mathematical problem and we are undoubtedly grateful for such people. ...


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You're wondering why pressure nodes form at an open end of a tube. The answer is, they don't! It's just a reasonably good approximation. Physically, consider the air molecules at the center of the tube. Since they're far away from the edges, there's no way for them to "know" exactly when the tube ends, so the sound wave must "leak out" slightly. The ...


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From the Wikipedia article on sound: In physics, sound is a vibration that propagates as a typically audible mechanical wave of pressure and displacement. To fully understand how is air vibrating in an open pipe, you have to consider not only the acoustic pressure wave, $$\frac{\partial^2 p}{\partial x^2}=\frac{1}{c^2}\frac{\partial^2 p}{\partial ...


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Whoa...whats that?sound waves travel faster in liquid than air; 4.3 times faster dependent on the temperature, The higher the elastic constant of the medium the faster sound travels and The tighter the molecular bond the higher the elastic constant. Light travels faster in air than water, simply because air is less denser than water.The denser the medium the ...


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It looks like a dubious exercise question, unless the pages preceding the exercise set up a framework of what kind of things you're allowed to assume here. Both the entrance and exit (speaker/ear) represent discontinuities in the acoustic impedance of the tube. The impededance of the speaker (will it absorb reflected acoustic energy or not?) is not described ...


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I know that speed of sound is independent of pressure No, it isn't. It's just not directly dependent on it so it's said that the speed of sound in gases depends on the temperature, molecular composition, and heat capacity ratio of the gas. But temperature and heat capacity ratio depend on pressure. Furthermore, the dependencies on temperature don't ...


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I think I did not get this completely, in particular how is the existance of the privileged frame translated in a different physical phenomenon in the cases in which the observer or the source move? Imagine a case where one of the two is at rest with respect to the medium and the other is moving away at $c$. If the emitter is moving, the receiver ...


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The only thing which matters is relative positions or velocities of two bodies. If you have only two bodies in a vacuum, then it doesn't matter which one is moving - what matters is their relative velocity. If you now have three bodies, say A, B, C then still what matters is their relative velocities. "A is moving 10 km/h while B and C are staying" is not ...


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No, the frequency will not change. If the wind is blowing at constant speed and the distance between source and observer remains constant, then the time it takes for a sound wave to get from source to observer will be constant. So the time interval between wave peaks (period T) when they are detected by the observer remains equal to the interval between ...


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Yes, it is possible but it involves a lot more work. The problem is that the different components you want to separate are not similar enough for a simple subtraction to work. The frequencies are far from exactly the same, and even if they were approximately similar the relative phases would change quite fast. The phase information cannot therefore be used ...


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As knzhou mentioned, this is true even for progressive waves in a string. Your mistake might be to think about simple harmonic motion instead of harmonic waves. I will show it for a progressive transverse wave in a string. It is easier to visualize. At the end I will give you a sketch for longitudinal waves. For a string of density $\mu$ and tension $T$ ...


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The speed of sound depends on the medium in which it travels. In air it can be affected by ambient temp, relative humidity , as well as atmospheric pressure. The speed usual quoted at a standard temp and pressure. http://byjus.com/physics/speed-of-sound-propagation/


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You know that sound is a longitudinal wave. It passes through a medium by pressurizing and depressurizing the medium. Solids are highly elastic than air. They are very hard to deform. So, they resist any change in the positions of the atom. Once disturbed, the medium develops a high restoring force to tend back to it's original position, but inertia causes ...


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Adiabatic bulk modulus of air $=1.4\times 10^5$ Pa and Young's modulus of steel $=1.8 \times 10^{11}$ Pa. Density of air $= 1.2 $ kg m$^{-3}$ and of steel $8050$ kg m$^{-3}$. The interaction between the atoms within steel is via the bonds whereas the interaction in air are by molecules colliding with one another and limited by the speed at which the ...


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It depends: 1) On whether you mean mass density or particle density, 2) on the temperature and type of gas. The main observation is that speed of sound is approximately independent of particle density, and mostly a function of temperature. 1) The speed of sound (squared) is given by the compressibility at constant entropy per particle $$ c_s^2 = \left. ...


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And actually at infinite Hertz, the air will not vibrate, so we'll hear nothing. And even if it does, our hearing ability is only till 20kHz. It'll be like passing direct current through a speaker, the membrane is vibrating, but unfortunately we hear nothing!


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Tpg2114 is right. It's the sonic boom. All the wavefronts in front of the airplane bunch up and add up, and you hear a thump. It travels with the aircraft. To go past it is like going through a barrier because of the high pressure there. Once you pass it the sonic boom trails behind the aircraft. See it at ...


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There is no such thing as "infinite hertz". The equation to calculate the doppler shifted frequency breaks down when the emitter travels at, or faster than, the speed of sound. What actually happens when an object travels that fast is the sound waves all pile together and form a shock wave. This is what creates the sonic boom.


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No, it is not true that sound travels faster in denser media. In fact it travels slower. In the adiabatic approximation we assume that the portions of the gas vibrate so fast that it is not able to exchange heat with the surroundings. The the longitudinal displacements can be shown to satisfy the wave equation $$\frac{\partial^2 u(x,t)}{\partial ...


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Energy is proportional to amplitude squared. The energy in the wave is spread out over the surface of a sphere. The area of this surface increases as the wave propagates outwards from the source and is proportional to $r^2$. So the intensity of the wave (power/area) decreases in proportion to $1/r^2$.


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Firstly, as you show, the decibel scale is a scale used to compare two levels: the one you're measuring, and another value. The definition of the decibel scale is:$$dB = 10 \times \log_{10} \left( \frac{I}{I_{Ref}} \right)$$where $I$ is the signal/sound/power that you want to measure, and $I_{Ref}$ is the value you want to compare it to. (If you want $bel$ ...


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For small enough amplitudes, the speed of sound is independent of how loud the sound is. It is also true that for a wide range of frequencies, the speed of sound doesn't vary with the pitch. When you move to large amplitudes (the assumptions of linear material are challenged) and high frequencies (when the wavelength of the sound is comparable to the spacing ...


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The speed of sound is determined by the "springiness" of air. Speed of sound in metals which have a much higher mechanical coefficient of expansion (compressive modulus, bulk modulus) is correspondingly higher. The longitudinal propagation of the sound energy does have an energy(intensity), but the value of that energy doesn't really affect the "spring ...


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When working with waves the wavelength and frequency (pitch) are inversely related. Sound waves have the relation frequency times wavelength equal the speed of sound. Wind instruments are using the longitudinal dimension of air in the instrument as a medium like a "string". In both the string and wind instruments, shorter wavelengths in the excited medium ...


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Wind instruments work by setting up sanding waves in the air column inside them. Shorter instruments have shorter air columns and thus standing waves with shorter wavelengths resulting in higher pitches.


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The energy of the wave is dependent on the amplitude of the wave. The amplitude is a measure of loudness of sound. Suppose we have a medium and all the particles in it are in equilibrium. Now we give a disturbance to a particle (or group of particles), which appears as a wave. The wave's velocity is dependent on the properties of the medium (this reasoning ...


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The propagation of sound over distance definitely changes with weather; but perhaps not the way you think. For example, it is my experience that if you stand at the shore of a quiet lake (say 1 km across) at night, you can hear sounds from the opposite shore. This is a result of changes in the density of the air, which gives a "focusing" effect. ...


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Clouds can form at a temperature minimum. Above the clouds the temperature may increase sharply. The sound speed increases $T^{1/2}$, so immediately above a temperature inversion, there can be a region of decreasing (sound) refractive index. This can have the effect of bending sound waves back towards the Earth. The phenomenon is more normally noticed on ...


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The only way to answer your question is by means of experimentation. As your post implies, the mind sure plays tricks on itself. And how we perceive the world is not how the world actually is. So get yourself a decent sound meter and get measuring! Should you find some effect the question then becomes "how and why?" That would be an interesting question ...


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If the source were truly point-like, yes. But nothing is truly point-like, so no: your formula for $I(r)$ is modified for short distances (where the inner structure of the source becomes relevant). This means that, if your source is a set of speakers, then $I(r)\propto R^{-2}$ is only valid for $R\gg\ell$, where $\ell$ is, say, the radius of the diaphragm of ...


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Your understanding of sound production and microphone operation seems largely correct. One thing though, a couple time you refer to air particles moving away from the sources which is incomplete. Sound is carried by a longitudinal wave. The air particles periodically move away from the source and back towards it. You can take a loudspeaker, seal it in a ...


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The attenuation of sound in air is a function of frequency - the higher the frequency, the greater the attenuation per unit length. There is also a natural limit to the amplitude of a sound wave: once the peak pressure is more than twice the ambient pressure, you no longer have a traditional "wave" since air pressure cannot go negative. Third - ...


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That is because of the termination impedances at the pipe end and mouth. The above described relationship for fundamental frequency is given for zero termination impedances (ideally open pipe) which is not the real case. The simplest way to account these impedances is to introduce corresponding length corrections, so for the $f_0$: $$ f_0 = ...


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There are many reasons why the answer to this question is quite complicated - but I am pretty sure that you are expected to treat the propagation of the sound as though it's spherical (I deduce this from the "assume the horn is a point source" instruction). The fact that the train is probably running on the ground means that you really only have a ...


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You can reasonably assume that whatever idea you have, it's been considered already. That's because the math is the same for all wave phenomena, and a course of classical mechanics shows you there aren't that many different ways of extracting distance information. You can have parallax measurements (measuring angle differences), and in the case of coherent ...


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A ratio of 1 to 3 is well within the regime where the wavelength is "similar" to the object size, and diffraction/scattering effects are massively important. Without even getting into the details of diffraction patterns (which make the difference between these frequencies even more pronounced than my simplified explanation suggests), if we suppose that the ...


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This is known as Helmholtz resonance. Essentially, the volume of air in the cavity acts as a spring where the spring constant is dependent on the volume of the air, and damping is dependent on the inertia of air in the neck of the bottle or container. The frequency is: or: frequency = speed of sound / 2 pi * sqrt (opening area / cavity volume * length ...


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I assume you are referring to what happens when such a plane wave is propagating parallel to a solid surface. You are correct that strictly speaking, the acoustic particle velocity, like the mean flow velocity, must obey the no-slip condition at the wall. Viscous effects become important very close to the wall only, such that the acoustic motions are no ...


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Refraction occurs because of a change of speed of propagation of the wave. When light passes from air to water it slows down, whereas when sound travels from air to water it speeds up. Therefore sound is refracted away from the normal, whereas light is refracted towards the normal.


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The speed of sound is greater in water than in air, so the wavelength in water is greater than in air. In effect the refractive index of the water is less than the refractive index of the air. For light it is generally true that the refractive index is higher for denser materials, and this is because light interactions mainly with the electrons in a medium ...


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In simple words its just like if you are standing in-front of a small wave you won't be affected that much when that wave hits you but if its a large one then you will definitely be affected a lot, its just all about force and pressure, the louder and bassy it gets the more the pressure and force that hits your heart mind ears and almost every part of your ...


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What you are hearing is mains hum: mains electricity is alternating current (ie the voltage is approximately sinusoidal and symmetric about zero), with a frequency of 50Hz or 60Hz. things like kettles and heaters use a lot of power and parts of them will mechanically change shape at this frequency, which is audible. This kind of physical noise from things ...


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Well, since this question is very well covered in literature, I will provide the first steps and you can do the discussion by yourself. Usually, the first approximation is planar wave in a duct of varying cross section area $S = S(x)$. The modified wave equation for such a case is called the Webster equation: $$ \frac{\partial^2 p}{\partial x^2} + ...


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From the library of expert witnesses: The fundamental theory for voice identification rests on the premise that every voice is individually characteristic enough to distinguish it from others through voiceprint analysis. There are two general factors involved in the process of human speech. The first factor in determining voice uniqueness lies in the ...



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