What is Sound: Definition and 1000 Discussions

In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimetres (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.

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  1. O

    What materials can transfer sound vibration?

    If water is hold inside the water bottle, which is made of plastic, and I play music within the room, can the sound vibration get through the plastic bottle and transfer it into water? Does anyone have any suggestions on what kind of materials to hold the water to get the best transfer rate on...
  2. FlexGunship

    Why do people complain about sound on LCD TVs?

    I'm looking for a 42" - 46" LED HDTV lately, and I keep looking at these TVs on sale that have incredibly low reviews and skipping over them. However, upon reading the "bad reviews" it seems everyone is saying "TV is fantastic, but the sound is bad." Here's just one TV for example...
  3. M

    Doppler effect, sound source and reflecting surface moving towards eachother

    Homework Statement A sound source A and reflecting surface B move directly towards each other. Relative to the air the speed of source A is 29.9 m/s, the speed of the surface B is 65.8 m/s and the speed of sound is 329m/s. The source emits waves at frequency 1200 Hz as measured in the source...
  4. A

    Proof Question Help (Deals with speed of sound in air)

    Homework Statement Using the equation P=m/V show that the equation PV=nRT can become P/p=(R/MW)T P=pressure p=density of air n=number of moles of gas R=gas constant T=temperature m=mass V=volume MW=mass of one mole of air Homework Equations P=m/V PV=nRT P/p=(R/MW)T The Attempt at a...
  5. M

    Diffraction of Sound: Exploring Why Wavelength Matters

    When the wavelength is bigger than an obstacle, then the sound waves bend around the obstacle. so why I can't imagine this at all I read this page and watched the animations of it but it doesn't tell me the answer http://www.acoustics.salford.ac.uk/feschools/waves/diffract.htm reflection of...
  6. T

    Troubleshooting Hardware Implementation: No Sound from Speaker

    I have done the hardware implementation using the planned schematic below. but somehow no sound seem to be able to play from the speaker except some noises. Anyone can help me check if something is wrong with DAC shematic...
  7. B

    Is it possible to reach speed of sound?

    Hi This is probably simple but i just can't seems to work it out: assume no gravity or friction: car 1 traveling at a constant speed of 50m.s in one direction Car 2 traveling at a constant speed of 50m.s on top of car 1 in same direction car 3 traveling at a constant speed of 50m.s on...
  8. J

    Factors that effect sound waves in water?

    1. For this question, I need to explain why sound waves emitted into ocean water sometimes fail to give accurate results. 2.I have thought about, the salt density and the waves traveling through different water temperatures, but need to expand on these two ideas and don't understand it enough to...
  9. R

    Sound pressure level at vacuum cleaner and earphones

    Hello, I have read that vacuum cleaner makes 70 dBa and earplugs can easily go beyond this. The problem I have is that I can hear my neighbor's vacuum cleaner thru wall easily. But if I set my mp3 player at max (should be around 100dBa according to manufacturer) I can heard this at few...
  10. M

    Hear Better At Night: Explaining Sound Refraction

    I am taking a physics class and need to explain why we can hear better at night than during the day.
  11. A

    Relationship Between Sound Intensity and Power?

    I understand the inverse square relationship between sound intensity (I) and distance (r). There was a misunderstanding in physics class today about the mathematical and theoretical relationship between sound intensity and power according to the equation: I = P/4∏r2 Sound intensity is...
  12. A

    If sound travels faster through solids then why can't we hear through doors?

    Why can't sound pass through closed doors?
  13. Y

    How is sound transmitted through air so clearly

    How is sound able to be transmitted through the air with such extreme clarity. What I find puzzling is that air has no stiffness to it at all. There are just countless numbers of molecules traveling at the speed of sound in random directions. How can a single speaker cone set up pressure...
  14. N

    Reference for the Temperature Dependent Speed of Sound in Common Solids

    Hi friends, I need the average speed of sound in some common solids, such as Si, Cu and Al, over temperature ranges from 100K to 500K. After 5 hours of surveying acoustic and physical properties handbooks and googling the web, what I find is almost nothing. Does anybody know a...
  15. L

    Sound Intensity and Sound Level

    Homework Statement The intensity of the sound from a certain source is measured at two points along a line from the source. The points are separated by 11.8 m, the sound level is 68.10 dB at the first point and 60.31 dB at the second point. How far is the source from the first point? d =...
  16. L

    Intensity of sound and finding distance from sound source

    The intensity of the sound from a certain source is measured at two points along a line from the source. The points are separated by 11.8 m, the sound level is 68.10 dB at the first point and 60.31 dB at the second point. How far is the source from the first point? Know: I = P/A =...
  17. S

    Q: A&B moving in opposite directions @ 0.6 c comparison with sound.

    I'm trying to understand relativity on a simple example: 2 objects A & B moving in exactly opposite directions at 0.6c each, starting from frame C at the center of things that remains stationary. So, we have: W <----0.6c A ...... C ..... B 0.6c----> E 1. From frame C, A is moving...
  18. J

    Light waves, photons; sound waves, phonons; water waves, hydrons ?

    Light waves, photons; sound waves, phonons; water waves, "hydrons"? Light waves are made of photons; sound waves are made of phonons; so are water waves made of "hydrons", and if so, how would they behave, and would it be possible to make a water laser or something similar based on these particles.
  19. P

    Why Does Sound from Above the Surface Sound Faint Underwater?

    When swimming underwater, why does sound from above the surface sound very faint? I know that the answer to this may be simple, but I just can't put my finger on the answer. I know that sound travels faster in water then it does in air, does this fact have anything to do with it? Thanks!
  20. B

    Why does sound pressure vary with 1/r?

    I didn't follow the template because this is more of a conceptual question that I can't get a clear answer for. I understand that sound intensity varies with 1/r^2 because the total intensity at a point in the wave is constant and if you have spherical propagation then the area of the surface...
  21. C

    Bulk Modulus and the speed of sound

    Why is it that materials with a higher bulk modulus value allow for sound waves to propagate through them faster? A material with a high bulk modulus requires a relative greater increase in pressure to contract by the same volume as a material with a lower bulk modulus, and as such sound waves...
  22. A

    Measuring sound velocity from a P-T graph?

    I don't have any specific numerical values for this, as it's a general question, but hopefully I explain it well enough using only words: If you plot a graph of position vs. flight time (of a sound pulse, for example), what is the slope of that graph going to be? (That is, what does the slope...
  23. D

    Definition of a baffled plate in the context of sound radiation

    Hi everyone, I've been reading quite a few papers on the study of sound radiation, and a common system that is studied is described as a "baffled plate". What exactly are the boundary conditions on a baffled plate? I thought it was simply that the edges have a pinned boundary condition, i.e...
  24. S

    How to find the wavelength of a sound wave?

    Homework Statement What is the wavelength of a 25 Hz sound wave? What is the wavelength of a 4.5 kHz sound wave? Homework Equations wavelength = velocity / frequency or λ = v/f The Attempt at a Solution I know that I'm supposed to plug the 25 into the equation, but he didn't give...
  25. P

    Research combining physics with sound, acoustics, music

    Hello! I am a recent university grad, majored in physics, with a strong background in programming and maths. I've had a couple non-physics research positions, and am looking to go back to school for a masters. All my life I've been very passionate about music, from composing classical...
  26. E

    Speed of sound in an ideal gas

    Homework Statement Determine the speed of sound in argon gas at 30 degrees celcius. Argon is a monoatomic gas with atomic mass 40. Assume adiabatic and ideal gas conditions. The mass of a nucleuon is 1.67*10-27 kg=mp. Homework Equations Adiabatic constraint: pVγ=constant. Ideal gas...
  27. L

    Array of underwater transducers for sound massage

    hello, since a while my mind is caught by an idea. This idea is concerned with underwater sound massage system. For this purpose i would like to build an array of underwater sound transducers, which can all be steered individually (to do a coarse beam forming). However, since i am...
  28. Ivan Seeking

    Mystery Sound Competition: Who Can Name the Source?

    I don't recall ever trying a mystery sound competition. So, in the fashion of other competitions, whoever can name the source of the sound picks out the next mystery. The imagery in this video is irrelevant and not intended as a clue or a false lead...
  29. M

    Help with physics, speed of sound?

    Homework Statement You see a neighbour in a cottage across the lake chopping wood. He is 2 km away and you see that it takes 2 s to hear each chop after you see it happen. Calculate the air temperature. (v= 332+ 0.6 T) Homework Equations v=d/t The Attempt at a Solution v= 1 km/s...
  30. H

    Why is sound more intense at night?

    why is sound heard more clearly in night than at day?
  31. F

    What's that sound on cars on a hot day?

    Like on a hot day, cars make these clicking sounds on the surface? Does having a silver or white-colored car make it worst? Because I've seen black -colored ones do that too
  32. M

    Sound Waves and Interference Problem - Check My Work?

    Okay, I have this problem worked out, but I have no clue if my answers are right. Could someone please check my work and give me some confidence or show me where I may have messed up. Homework Statement Two loudspeakers, one of them generates sound with 400 W power the other with 100 W. The...
  33. atyy

    Is This Gauge Theories' Classification Similar to LQG?

    http://arxiv.org/abs/1108.4389 Gauge Theories Labelled by Three-Manifolds Tudor Dimofte, Davide Gaiotto, Sergei Gukov (Submitted on 22 Aug 2011) We propose a dictionary between geometry of triangulated 3-manifolds and physics of three-dimensional N=2 gauge theories. Under this duality...
  34. B

    How Does Sound Travel on the Moon?

    can we hear the sound of our steps in moon?
  35. L

    Why does bass have a higher tendency to move objects compared to treble?

    So, I'm writing a music A-Level dissertation, but because of my love for physics, I've based it on the physics of sound. I didn't think this should go into the homework section because it's not so much homework that I need help with. Whilst working through some fundamentals on my board, I...
  36. M

    Can Snell's Law Be Proven Mathematically for Sound and Light Refraction?

    when light rays fall perpendicularly on a separating surface between two media it doesn't refract according to Snell's law and it is the same with sound waves how to prove something like that mathematically?? Thanks in advance
  37. R

    What is the mechanism of small holes in auditorioms used as sound

    what is the mechanism of small holes in auditorioms used as sound absorbers
  38. V

    Calculating the energy loss due to sound emission on collision

    Homework Statement I am writing my Extended Essay for IB, where I look at the possibility of obtaining accurate results in open system of a school, by accounting for all energy losses that occur during the investigation. Before conducting my experiments (which included an air track with two...
  39. R

    Suggest me some low sensitive Sound sensors.

    I am doing a module to adjust the noise in a motor such that motor inside piston stroke is touching some mechanical part leads to small noise. I would like to adjust these by using sound sensoror presser or vibration sensors. I don't know which one to use in that sistuation but my guess is sound...
  40. M

    Why does sound reflect and create an echo in certain conditions?

    1-why does sound intensity increase at night? 2-what makes diffraction of sound more observable than diffraction of light? 3-reflection of sound takes place when it falls on a reflecting surface whatever the distance between the vibrating source and the surface but in case of echo there are...
  41. T

    Two Questions: viscosity and sound

    ive got two basic questions. 1: Does density effect viscosity, as in is it possible to have a highly dense but low viscosity fluid and vice versa. 2: I know in space there's no sound but can you hear your own heartbeat and other internal vibrations?
  42. X

    Pipe and speed of sound question

    Homework Statement A student holds a 325.6 Hz tuning fork near the end of a pipe that is closed at one end. He notices that resonances can be heard for several different lengths, one of which is 55.5 cm. He gradually lengthens the pipe to 92.5 cm where he detects the next resonance...
  43. F

    Sound intensity and distance problem

    Homework Statement Henry and Tom see a flash of lightning and then hear the resulting clap of thunder. Henry measures the sound level of the thunder as 65 dB while Tom, who is 800 m further from the event, measures it as 63 dB. Homework Equations The Attempt at a Solution I_H /...
  44. D

    Increased Density Results in Decreased speed of sound?

    According to the equation c=√(C/ρ) where c is the speed of sound, C is the coefficient of stiffness and ρ is the density of the medium throughout which a sound is played the speed of sound should acctually decrease with an increase in density. Why is this so? I would've thought that increasing...
  45. I

    How difficult does this schedule sound?

    3rd Semester Schedule Introduction to Differential Geometry Introduction to Real Analysis - using Rudin Advanced Linear Algebra Symbolic Logic (philosophy course) Intro Programming (Java) I have some experience with proofs in LA, read up on basic techniques of proof over summer...
  46. K

    Sound waves versus equilibrium

    Postulate a parcel of air that is transmitting sound waves. Can that parcel ever be considered to be in a state of equilibrium? I maintain that it cannot. How say you?
  47. J

    Create Sound-Activated LED Circuit: Subwoofer & Floor Speakers

    So I was wondering how to create a sound activated LED circuit for each of my speakers. I want the red LEDs to light up when the subwoofer is activated and the blue LEDs to light up when the left and right floor speakers are activated. I had a thought about wiring the LEDs parellel to in input...
  48. C

    Sound Intensity- just need someone to check my work

    Sound Intensity-- just need someone to check my work :) Homework Statement While enjoyable, rock concerts can damage people's hearing. In the front row at a rock concert, 5m from the speaker system, the sound intensity is 145 dB. How far back would you have to sit for the sound intensity...
  49. O

    Can we break down a single noise into individual soundwaves?

    Greeting Physics Forums; my first post here. Thanks in advance for your time! Approximately how many soundwaves compose what we can say is a single noise, like a drumbeat? I know there are multiple frequencies involved and our brain interprets this in it's own way. There is interference...
  50. T

    Sound Laser? Focus Sound Like Laser?

    Is there anything that focuses sound like is done with a lazer? That is where you wouldn't be able to hear anything unless you were in the beam path and maybe the intensity would be magnified.
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