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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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What is the suitable form of plane wave expansion?

This question is in Acoustics area. Consider we have a common progressive monochromatic plane wave which is going in an ideal fluid toward an object. The point is that object has symmetry in terms of ...
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0answers
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Variation of speed of sound with humidity and temperature?

I am building a sonar using Arduino and I needed to accurately use the speed of sound. I also have a humidity and temperature sensor, and I wanted to know what is the formula for the speed of sound ...
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Surface acoustic wave devices, is this a resonance effect or forced oscillation?

I have been thinking about SAW devices the the way the inter-digital transducers (IDTs) launch acoustic surface waves. But I am unclear whether this is a resonance effect or forced oscillations. As ...
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Find the frequency of tuning fork [on hold]

Q. Two tuning forks A & B give 5 beats/sec. The frequency of A=512. When B is filled, 5 beats/sec are again produced. Find the frequency of B before and after filling.
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4answers
3k views

How are overtones produced by plucking a string?

I read the following from wikipedia: When a string is plucked normally, the ear tends to hear the fundamental frequency most prominently, but the overall sound is also colored by the presence ...
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1answer
14 views

Subwoofer Efficiency Ratings have Inverse Effects in Small Enclosures?

I found this article on the internet which claims that higher sensitivity subwoofers have lower output in smaller boxes. http://stereointegrity.com/wp-content/uploads/Efficiency.pdf Is this true or ...
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1answer
20 views

Noise level x amount of meters away from an outdoor singer: sphere or semi-sphere?

When computing the noise level x amount of meters away from a singer who is singing outdoors, should one rely on the standard formula $I=\frac{P}{4πr^2}$ (and then convert 'I' into decibels) or ...
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2answers
83 views

Do whales in ocean use hyperbolic geometry to communicate? [on hold]

Since the speed of sound increases with depth in an ocean, the shortest time for the sound to travel between points $A$ and $B$ may be a curved path. But does sound actually take this curved path ? I ...
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2answers
51 views

Speed of sound in a gas and speed of a typical gas molecule

Why is speed of sound in a gas less than the average velocity of the gas molecules? Is there an intuitive way to explain this?
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1answer
49 views

Closed End Waves [closed]

Why is phase difference between P and Q =0?
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1answer
39 views

Difference between speed of sound into a star

I try to understand the following graphics with x-axis being the radius of a typical star : I would like to knwo if $\delta c/c$ represents the relative error between theorical and experimental ...
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2answers
42 views

What is the difference between natural, fundamental, resonant, and forced frequencies?

I'm just overall slightly confused on their exact definitions, as they get thrown around a lot.
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Bleding in convolution reverb

Since I use crystallography a lot in my studies I know that, when light or X-rays are considered many error and abberations add up to a total by the means of mathematical convolutions. So in order to ...
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4answers
57 views

Does sound bounce in all directions, or as a ray, like light?

When light is shined on a perfectly smooth surface it reflects from it as a ray, going in only one direction. However, from my reading of Rayleigh's Theory of Sound he describes sound waves as ...
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2answers
370 views

Is a flame whistle, pipe organ or flute possible?

Could one arrange a simple candle or wick oil lamp in a way that it would make a sound while it is burning? A simple device without a Sterling engine etc. Does the rising hot air have enough energy ...
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1answer
58 views

When a pen is thrown on the ground, why doesn't the whole pen seem to be vibrating even though it makes a sound?

Is that because the vibration is reflected back by the boundaries of the pen, a standing wave is produced, and the nodes are so close and so numerous that it seems like the pen is not vibrating at all?...
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3answers
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How to rigorously analyze dissonances of a perfect fourth and perfect fifth played on a monochord?

I'd like to give a rigorous analysis of the "dissonance" of musical intervals -- say, a perfect fourth versus a perfect fifth. I think one way to get "rigor" here is to consider the frequencies and ...
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8answers
15k views

Why does fire make very little sound?

Sound is air particles vibrating (thus hitting each other to make longitudinal waves) and heat is the vibration of air molecules. Because we can only assume that heat made from fire is a higher ...
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1answer
22 views

Question about sound generation

If I have a membrane, and I bring it into vibration, than it emits a sound. I thought, that the sound frequency is determined by the velocity of the vibrations and the loudness (soundpressure) is ...
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1answer
21 views

Loudness of air movement

Is the soundpressure, which is created by air movement, the same as if it is created by sounds? If you use a microphone with a pop filter and without a pop filter and you blow into it, than there is a ...
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3answers
78 views

What happens in an organ pipe at frequencies other than the harmonics?

I learned that, at frequencies corresponding to harmonics, standing waves are formed. But what actually happens at other frequencies? Won't the reflected wave superimpose with the original wave? Do ...
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1answer
33 views

Various regions of fluid flow

In the image above, there is this plot between sound velocity and flow velocity. I want to check if my interpretation of the plot is right or not. Here are my observations: (1) The c-a plot is a plot ...
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2answers
53 views

Do speakers have non-radiating nearfield?

Antenna nearfield contains energy that is not radiated away,does speaker or any other acoustic device nearfield also have this non-radiating energy element that exist in space and doesnt travel away?
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1answer
27 views

In what cases should plasmas be considered compressible?

I was listening to a lecture where it was mentioned incompressibility was assumed during derivation of an electrostatic instability, but incompressibility was not assumed for an electromagnetic ...
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0answers
73 views

Negative mass of sound waves?

I have just discovered multitudes of pop science articles promoting a recent arxiv paper, "The mass of sound"[https://arxiv.org/abs/1807.08771 ], which claims that sound waves have negative ...
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2answers
81 views

Sound beats mathematical expression

I am reading about sound beats. According to the superposition principle, if at a certain position the two waves are given by, let say, $$\ y_a(t)=Asin(2\pi f_at)$$ $$\ y_b(t)=-Asin(2\pi f_bt)$$ ...
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0answers
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Advice on debugging ultrasound standing wave setup

I'm trying to set up an ultrasonic standing wave powerful enough to levitate polystyrene - on a budget (i.e. nothing's quite what I'd like it to be ;)). I have not yet successfully demonstrated a ...
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0answers
25 views

Speed of sound for a given frequency in a non-ideal gas (humid, room temperature air)?

I'm trying to understand what the speed of sound might be like for a given frequency in non-ideal and non-dry air. Wikipedia states that speed of sound has a weak dependence on frequency in ordinary ...
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2answers
47 views

How do surfaces give out sound by friction, when its said that bodies dont actually touch?

So due to electron-electron repulsion, isnt it true that surfaces dont really 'touch'? If so, then how do two things rubbing each other give out sound due to friction? or is that because the uneven ...
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1answer
24 views

Tools for measuring vibration/sound of shaking

I would like to know how I can measure the vibration coming from my hand shaking something. My experiment is like this. I put a ball made of strong glass into a closed empty box made of strong glass ...
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1answer
26 views

Why is the contour of a stream function the same as the streamline?

I am studying acoustic streamlines. As this paper Singular points of intensity streamlines in two-dimensional sound fields says the level curves or contours of stream function represents the ...
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0answers
31 views

Intensity of sound and pitch perception

I read in "Handbook of Acoustics" by Alton Everest A famous acoustician, Harvey Fletcher, found that playing pure tones of 168 and 318 Hz at a modest level produces a very discordant sound. At ...
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1answer
47 views

Doppler Effect and Speed relativity [closed]

I calculated that the frequency of the sound that reaches a recipient achieved when the recipient remains stationary and the source is towards him (vS = 34m / s) is not equal to the frequency of the ...
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1answer
23 views

Creating negative phase audio “voices” inside ambient sound

Is it possible to use a sample recording of a voice, then using the negate (180 phase) of ambient or white noise as a "brush" of sorts to create the negative of the voice as a cutout of the ambient ...
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1answer
29 views

What physical properties determine the sound of a drum head?

I am working on a rubber substitute for a leather-membrane drum. The objective is to replicate to reasonable extent the "sound" or timbre that the leather drum head makes with a rubber drum head as ...
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1answer
35 views

What causes noises in the house such as pops, creaks from walls, car windows, TV and wardrobes? [closed]

Here in the Middle East ,as you know, the weather is hot outside and we have air conditioning inside our homes / offices and cars. Sometimes there are noises in the house like pops or creaks from ...
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1answer
89 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?
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1answer
19 views

Does a helmholtz resonator have a standing wave inside the volume at the resonant frequency?

If one were to exercise a resonator at the resonant frequency and you were able to measure the pressure at all points within the volume at a particular moment in time would the pressure be uniform at ...
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2answers
31 views

Doppler Effect and Energy variation

In the Doppler effect, we see that the frequency of sound that the observer hears changes according to the motion of the observer and source. For example, if the source is moving towards the observer, ...
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0answers
17 views

Sound Waves and Random Walks

Is it possible to explain/study sound waves using random walks? If yes, how will you do it. This question is related to me reading somewhere that woodwind instruments are possible in 3 dimensional ...
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1answer
43 views

Noise cancellation device for entire rooms [closed]

I recently met a group who were exploring active noise cancellation devices for entire rooms. Their approach essentially revolved around detecting incident noise on the room and blasting inverse ...
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2answers
79 views

Can ultrasonic waves become audible after “hitting” some object?

I recently found this article published in an Asian magazine, which claims the possibility of turning ultrasonic waves into audible sounds after "hitting" an object. A Japanese enterprise specialized ...
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2answers
92 views

Why is sound produced when we hit a metal? [duplicate]

We all know that metal are sonorous and produce sound on hitting but why is sound produced I thought that it might be a way of energy released on inelastic collision but then why not heat as heat is ...
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1answer
18 views

Interpretation of the linearized conservation of mass in acoustics

I am studying how the acoustic wave equation is obtained from the conservation of mass and the conservation of momentum. The following picture gives two forms the conservation of mass equation, but ...
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1answer
47 views

Guitar string - feedback from the body

This is a question about the frequencies that remain on the string during the decay of vibrations. As I understand it decay occurs because of the: a- Internal damping of the string. This is due to ...
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0answers
29 views

Is there a machine that can turn high frequency sound into low frequency sound?

Say you had an annoying device emitting a high frequency hum through a hole. Could you fit something to that to turn the high frequency sound into low frequency sound of the same energy (so it would ...
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1answer
28 views

What is the difference between sound and vibration?

As far as I know, the only difference between sound and vibration is that sound propagates but vibration does not. In most cases, they are the same. Please help clarify these concepts.
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1answer
32 views

Determining the origin of the more dominant sound produced by two colliding bodies

When two objects collide, such as your hands clapping together, how do you determine if the sound being produced is predominantly coming from the physical collision of the two objects, or from the air ...
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1answer
21 views

What is the cause of sound produced by suction cups?

A partial vacuum is created when suction cups are pushed on to a smooth surface, and a distinct sound is produced when they are pulled apart. Why is this sound produced?
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1answer
90 views

Why pressure is a scalar instead of a vector? [duplicate]

I know by definition that the pressure is the ratio of the force, which is perpendicular to the surface, to the area of that surface and it has no direction. But I am confused by the two questions ...