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.

learn more… | top users | synonyms (1)

15
votes
3answers
1k views

Why do I always hear remote train horn at night?

This is definitely not an illusion, as many people have the same experience. I have usually lived in places miles away from train stations, which makes it unlikely to hear any train horns during the ...
0
votes
0answers
15 views

How far is the range of an ultrasonic sensor as far as it can transmit? [duplicate]

How far can ultrasonic waves propagate in the air? (if the energy is enough), how far can ultrasonic waves propagate in the ground (concrete floor)? Are there any articles or experiments about ...
0
votes
0answers
14 views

When longitudinal waves and transversal waves enter air from a soild, what will happen? How do waves transform?

When ultrasonic waves meet the interface (surface) between two media they will reflect and refract. What is the effect of the acoustic impedance on reflection? Is there any list about acoustical ...
3
votes
2answers
109 views

Sound difference between musical instruments [duplicate]

I know that the difference between two musical notes is given by the sound frequency, and the difference in volume is given by the amplitude. What I am wondering is why does the same note sound ...
2
votes
1answer
75 views

What happens to the energy?

if we make a bell ring in a vacuum room for 5 mins. And then open the door, will be able to hear the sound? If no sounds vibrations are emitted to the environment what happens to the energy that ...
1
vote
1answer
50 views

Dimensions of wave equation

If you take the homogenous wave equation: $$-\Delta_x u(x,t) + \frac{1}{c^2} \frac{\partial^2 u}{\partial^2 t} (x,t) \ = \ 0 \ \ \mathrm{in} \ \Omega \times (0, \infty),$$ with some proper initial- ...
2
votes
3answers
65 views

Is sound relative when travelling fast?

If I was listening to music through my headphones and travelling close to the speed of light and time is slowing down around me , would the music slow down as well?
9
votes
4answers
189 views

Is magnetic levitation a good way to vibrationally isolate a speaker from its support?

I recently heard about this company planning to sell a magnetically levitating bluetooth speaker. I understand that the levitation is partly motivated by visual aesthetics, but on the website the ...
2
votes
1answer
45 views

Energy estimation of an acoustic wave

I have an issue with 2D acoustic wave field modelling. In order to estimate the energy propagation direction of an acoustic wave I use Poynting vectors $S$ which can be described by $$ \vec{S} = - ...
1
vote
1answer
65 views

What are the similarities and differences between speech and music sounds?

From an acoustic perspective, I guess speech sounds are produced by varying/manipulating: resonance (shaping the cavity; something to do with harmony?) f0 (the length of the string/pipe/whatever) ...
2
votes
1answer
56 views

Longitudinal waves in a large (infinite) solid block

Specifically, I am trying to roughly determine the sound produced by a ball when it hits the floor and bounces. If the ball exerts a pressure onto the floor, then certainly this pressure will go on to ...
0
votes
0answers
21 views

Dispersing ultrasound in a tube - patters

I am looking for patterns to efficiently disperse reflected ultrasound in the range of wavelengths 1mm to 4mm within the interior of a narrow tube (I do not want wall reflections). For various reasons ...
1
vote
1answer
55 views

The inverse square law of sound through solids?

We all know about the inverse square law of sound. In short the power of the wave will get evenly spread on an ever increasing spherical expansion and this will dissipate the power of the wave at a ...
0
votes
0answers
54 views

Designing a home theater room for optimal acoustics

We are building an addition on our home that will allow us to build a basement home theater room with some level of flexibility regarding its size and shape. I've been reading somewhat conflicting ...
6
votes
1answer
133 views

Does a square wave “smooth out” in the air?

I understand that playing a square wave from speakers cannot produce a PERFECTLY sharp division between compression and rarefaction. But it's sharp enough to sound distinctly different from a sine ...
1
vote
0answers
21 views

Could symmetric molecular stretching cause a physical object to become amorphous? [closed]

I understand very little of this, but my google-foo has yielded me next to nothing, I thought I might then just ask. My real question here is if it might be possible through the use of vibration to ...
1
vote
1answer
64 views

What frequency of sound waves produces the most vibration [closed]

The name of the question is rather contradictory and counter-intuitive since sound is produced by vibration. However, very low frequencies around 32Hz and receding are bass. From what I have read ...
5
votes
2answers
255 views

Speed of sound in gaseous medium

Why does the speed of sound decrease as the density of the medium increases? I know why this happens mathematically, but I want to know what happens at the molecular level that results in higher speed ...
2
votes
2answers
87 views

Do we hear sounds differently on the highest mountains?

Some searching gives that above 6,000 meter altitude the air density is less than half of that at sea level. Speed of sound is about 15-20% slower and "acoustic impedance" seems to change too. Do ...
1
vote
1answer
50 views

Woodwind instruments overtones [duplicate]

When playing woodwind instruments, e.g., flute, if one blows harder, the sound will be one octave higher. Even harder gives even higher overtones. Does anyone know why?
2
votes
1answer
64 views

From where does the sound come from when two charged objects meet in real life?

I am sure all of us have played with rubbing things and producing static electricity and when I was charging my comb by rubbing it on my hair and watching it attracting a small piece of paper, I heard ...
1
vote
3answers
108 views

It seems that the harmonic (integer multiple) overtones of a sound usually all have the same phase. Is this true, and if so why?

And if you were to give each of them different phases, would the sound start to sound "off", or would it sound the same? All the same frequencies would be present, which makes me think it might sound ...
0
votes
4answers
186 views

How far can one hear sound?

I was thinking how far can I hear sound coming from a concert. Today I was walking at night and I could hear sound from somewhere very far. I started following the sound but sound used to disappear ...
4
votes
3answers
606 views

Calculate loudness of sound: why am I getting contradictory answers?

I know of events that are happening about 45 KM away from me which are said to be 210 or 213 dB at 75 meters distance from multiple sources. I think that I can hear them, so I did the obvious: $$ ...
1
vote
1answer
26 views

Resonance of a tube of air in case of more complex shapes

I've been thinking about posting this question on Music Performance stack, but finally I think it fits more here since I'm interrested in technical details. The subject of resonance of a tube of air ...
15
votes
4answers
2k views

Why do bubbles make a sound?

I have an understanding of how bubbles work. They encapsulate air (or other fluids) in a membrane caused by surface tension. When they pop, there is often a sound. Sound is a type of energy, kinetic ...
21
votes
3answers
829 views

Physics of weird “boing” sound in racquetball courts?

While playing racquetball, I frequently hear a very prominent "boing" sound (or more formally, a chirp). For example, you can hear it in this video when the ball hits the front wall. Does anyone know ...
-2
votes
1answer
50 views

Resonant Frequency & Opera Singers [closed]

Would it be possible under math of strings to note the frequency of each string vibrations? And in doing so, in hand with using the technique opera singers use to shatter glass with their voice, would ...
0
votes
0answers
30 views

SInce heat is a vibration in solids, isn't it just small scale sound? [duplicate]

On an atomic scale I think of electrons hitting positive ions in an electric lattice. Most energy there is heat energy. If I think of ball bearings flying through a large lattice, I think sound is ...
3
votes
2answers
61 views

Standing sound wave in a wind instrument

So I've had this question bugging me ever since I saw sound at physics class: How is it possible to match the resonance frequency of a column of air in an organ pipe and form a standing sound wave by ...
1
vote
0answers
52 views

How far can a voice carry through the desert at night? [closed]

Let's use these conditions: temp = 7C, relative humidity = 10%, air pressure = 85 kPa, elevation = 1500m, shouting at 100dB (not sure if this is a reasonable volume). Given these conditions, what ...
2
votes
2answers
157 views

Can we measure temperature of a object just by the sound it makes?

I been thinking if temperature is a basic property of macroscopic objects rather than of quantum or microscopic objects and it is as a result of average kinetic energy of particles residing in the ...
5
votes
2answers
802 views

Negative sound rooms

Well it is pretty well known that rooms with sound less than zero decibels, $\approx$ -15 decibels. How is it possible to create a room which is quieter than soundless? And it is claimed that just ...
1
vote
1answer
193 views

Compression vs Rarefaction in Sound Waves

I am currently looking into solutions for Sound Classification, and I came across Ludvigsen's methodology (if anyone wishes to refer to it). The problem is that a sample graph of amplitudes in one of ...
0
votes
0answers
25 views

A sonar continuously emits x(t), a general but known waveform and is reflected by a target. hypothetical question

A sonar continuously emits x(t), a general but known waveform that is reflected by a target and received by the sonar. Both the sonar and the target move in the 3-dimensional space in a general but ...
5
votes
1answer
73 views

Why does a wall act as a low-pass filter?

Learning about the fourier transform and its connection to filtering/convolution got me curious about naturally occurring filters. Why/how is it that brick walls naturally act as a low-pass filter ...
4
votes
2answers
68 views

How much does the sound definition vary during an LP (Vinyl)?

This question came to me when I realized how the linear speed varies while listening to a Vinyl LP. The linear speed variation has to be compensated with a variation in the resolution of the grooves, ...
7
votes
2answers
91 views

How quickly should a fluid come to hydrostatic equilibrium?

Let's say I'm holding a one-liter water bottle, full of water, which I then drop. Before dropping the water bottle, the equilibrium is for there to be a pressure gradient in the water canceling the ...
0
votes
1answer
94 views

Questions related to resonance/standing-waves and sound

I understand resonance for a simple harmonic oscillator but not for more complex systems like standing waves. How can I be in resonance with the normal mode in an organ pipe? I understand that the ...
41
votes
1answer
2k views

Why does our voice sound different on inhaling helium?

This question (and answer) is an attempt to clear the air on what appears to be a very simple issue, with conflicting or unclear explanations on the internet. Arguments, negations, etc are invited. ...
1
vote
1answer
31 views

Compute impulse response of a cavity for sound waves

Given a (closed or not) surface and a point emitting a spherical sound wave, how can I calculate the wave amplitude in any point of space, considering reflections on this surface ? The idea is to ...
0
votes
1answer
42 views

(air pressure and displacement) Isn't this image wrong?

Isn't this figure wrong? P(x,t) = -B(dy/dx) . If the derivative of air displacement has a maximum, then this is where the pressure is minimum, not maximum as this figure suggests. Could someone ...
0
votes
1answer
63 views

Using Audacity to generate power spectral density

Say I record something with a sound recording program like Audacity (e.g. plucking a guitar string). How could I use that recording to plot a dB vs Frequency graph?
0
votes
1answer
64 views

Need help with this derivation (Sound intensity)

I will copy a little bit of what my textbook says. By the way, we're talking about sound here. $$Intensity = (0.5)BwkA^2$$ The textbook claims that by using the relationships $w=vk$ and ...
202
votes
4answers
36k views

Can I compute the mass of a coin based on the sound of its fall?

Other day, I bumped my bookshelf and a coin fell down. This gave me an idea. Is it possible to compute the mass of a coin, based on the sound emitted when it falls? I think that there should be a ...
29
votes
3answers
2k views

What is the minimum pressure of a medium for which a sound wave can exist?

At what pressure will be particles in a medium be unable to form a sound wave when disturbed? How can this pressure be described mathematically? My guess is that this would correspond to the point at ...
1
vote
1answer
54 views

Why does lightning cause sound?

If I understand correctly, lightning is the discharge of electricity from the atmosphere into the planet. However, if I switch on a lamp, the wires are not causing thunder (or any audible sound). ...
5
votes
1answer
120 views

Is the mathematical form of the acoustic diffusion equation present in other fields of physics?

We are working in the field of High Performance Computing and we have developed a very efficient parallel implementation for solving the Acoustic Diffusion Equation as described below: $$ ...
0
votes
1answer
19 views

How to compute $L_{\rm eq}$ from temporal pressure data

I have pressure vs time data. how can I compute sound equivalence Level $L_{\rm eq}$ in decibels? can this be done from a frequency spectrum assuming that it is constant?
0
votes
2answers
99 views

can silence happens when 2 sound waves destroy each other [duplicate]

Hi is there any possibility that you located between 2 sound sources and u hear nothing? as we know 2 wave in opposite direction will destroy each other...